Facts for Faith

Issue 7, 2001

Articles

* Due to copyrights, original graphics and tables do not appear in these articles

The Dynamics of Dating

By Roger C. Wiens, PhD.

(Spanish Version)

Bewildered, Janet watches her son gaze in awe at the dinosaur exhibit. A sign tells her that the Tyrannosaurus Rex is millions of years old. But last Sunday, her Bible teacher stated emphatically that God made Earth only six thousand years ago. The confusion over dates makes her stomach churn. The age assigned to the fossils in front of her seems to contradict the creation account, and Janet’s heartbeats accelerate at the implication. Is Earth young or old? If old, did that mean the Bible is wrong? Or could science be wrong? And what is she going to tell her son?

Scientists agree that radiometric-dating techniques offer the most concrete evidence of any dating system for answering questions about the age of Earth. Yet, many people challenge the accuracy of radiometric dating, and misinformation describing the various radiometric techniques abounds. Debunking mysterious and complicated explanations of radiometric dating can be accomplished with a simple understanding of its general principles. Credible answers to common misconceptions about radiometric dating and a proper understanding of Scripture can help people like Janet reconcile creation accounts regarding the age of Earth.

General Principles of Radiometric Dating

Radiometric dating can be compared to an hourglass. When the timepiece is turned over, sand grains fall from the top of the hourglass to the bottom. No one can predict the moment when a particular grain will fall through the neck, but an estimate can be made for how long the whole pile of sand will take to fall.

A similar process takes place with the radioactive decay of atoms. (For a brief science review, see sidebar and figure 1.) The timepiece that allows dating is the “radioactive” decay of certain kinds of atoms from one form into another. Radioactive decay results from unstable combinations of protons and neutrons in the atom’s nucleus. Though most atoms contain stable nuclei and do not decay, some types do. When radioactive decay occurs, no one can predict which individual atoms will decay when. But, for a large number of atoms, the number that will decay within a given time can be predicted. The original (parent) atom changes into a daughter atom having different chemical properties.

However, one significant difference exists between radiometric dating and the hourglass design. Unlike the hourglass, the rate of radioactive decays in a rock depends on the number of parent (original) atoms at any given time (N0). As fewer parent atoms are left, fewer decays occur. If it takes a certain length of time for half of the parent atoms of a radioactive isotope to decay (half-life), it will take the same amount of time for half of the remaining parent atoms (a fourth of the original total) to decay. In the next interval, with only a fourth remaining, only an eighth of the original total will decay. This produces an exponentially decreasing curve as described by the equation and displayed as the decreasing curved line in figure 2.

All radiometric dating is based on this very simple equation and the exponentially decreasing curve. In other words, N is the present abundance of parent atoms, the original abundance of parent atoms equals N0, t is time, and k is a constant related to the half-life (the time it takes for half of the parent atoms of a radioactive isotope to decay). The simplicity of this equation combined with the fact that it works with many different dating methods produces great confidence in its reliability.

An hourglass measures the specific amount of time that has passed since being turned over. Radiometric dating also tells how much time has passed since a particular event took place. For igneous rocks (those formed from magma or lava), the method measures how much time has passed since molten material cooled and turned into rock. In other cases, the event may be the end of a period of metamorphic heating (e.g., heating to over a thousand degrees Fahrenheit underground) or, for radiocarbon dating, the length of time since a plant or animal died. The different dating techniques provide accurate timetables for determining the age of rocks or other artifacts.

The Accuracy of Radiometric Dating. Though work on radiometric dating first started around 1910, relatively slow progress was made before the late 1940s. Many dating methods have now been tested and retested for over fifty years. Radiation detectors measure the half-lives of radioactive isotopes either directly by counting the number of atoms decaying in a given amount of time from a known amount of the parent material, or by measuring the ratio of daughter-to-parent atoms in a sample that originally consisted of parent atoms only. While the number of atoms to decay in fifty years may be a small fraction of the total, extremely precise counting of the daughter atoms can be accomplished.

Table I gives the half-lives for a few of the most commonly used radiometric dating methods. The uncertainty levels of these half-lives are very small—only about plus or minus 2 percent for all except for rhenium (5%), lutetium (3%), and beryllium (3%).1 At this level of certainty, though an age may vary by a small percentage, no question remains as to whether Earth was created recently, or a long time ago. However, to measure ages of things accurately, one must apply the appropriate dating method.

Which Dating Method is Appropriate? A number of different devices measure time in everyday life. A stopwatch measures time in a one-hundred-meter race. An ordinary alarm clock measures how long a person sleeps. A calendar counts the number of days before Christmas. A calendar can't measure time in the one-hundred-meter race, and a stopwatch can't measure the days before Christmas.

As with other timepieces, radiometric-dating methods must be appropriate to the sample being dated. Though many people are familiar with carbon-14 dating, this technique dates organic material such as bones, wood, cloth, paper, and other dead tissue from either plants or animals and is not effective for determining the age of rocks. The best results are usually obtained if one uses a method whose half-life lies within a factor of ten of the sample’s estimated age. In the rare case that prior clues are absent, trying more than one method in order to obtain the correct age may be required. If the first attempt yields insufficient daughter atoms, a method with a shorter half-life needs to be tried, or samples with more parent atoms should be used in order for more daughter atoms to be present.

Most of the dating methods being discussed in the following paragraphs apply well when determining how long ago igneous rocks cooled and hardened from magma or lava. Atoms usually mix well in a liquid such as magma. When the molten material cools and hardens, the atoms no longer freely move about. Daughter atoms from radioactive decay occurring after the rocks cooled become trapped where they originated within the rocks. Like the sand grains accumulating in the bottom of the hourglass, the age of the rocks can be determined by measuring the number of daughter atoms and the number of remaining parent atoms, then using the half-life to calculate the time it took to make those daughter atoms.

However, a small complication remains. One cannot always assume that no daughter atoms existed to begin with, so the initial amount of the daughter product must be determined. Each dating method solves this problem in its own way. Particular types of dating work better in some rocks; others perform better in other rocks, depending on the rocks’ composition and age.

Examples of Individual Dating Methods

Over forty different radiometric dating methods have been successfully used. Of these forty, three brief examples show how some of these methods work.

Potassium-Argon. Potassium, an abundant element in Earth's crust, has one radioactive isotope, of which 11.2 percent becomes the gas isotope, argon-40. Whenever rock melts and becomes magma or lava, the argon gas tends to escape. When the molten material hardens, argon (produced by later decays of potassium-40) is once again trapped. In this way, formation of an igneous rock resets the potassium-argon clock. The geologist simply measures the relative amounts of potassium-40 and argon-40 to date the rock.

However, there are often instances of small amounts of argon remaining in the rock when it hardens, due either to trapped atmospheric argon or from argon escaping from decays deep underground. Air argon can easily be corrected for. But the argon from underground can have a higher concentration of argon-40 escaping from the melting of older rocks. Called parentless argon-40, its parent potassium does not come from within the rock being dated, nor from the air. In these slightly unusual cases, the date given by the normal potassium-argon method is too old. However, scientists in the mid-1960s came up with a way around this problem—the argon-argon method.

Though understood for over a third of a century, groups critical of dating methods seldom discuss the argon-argon method. This method uses exactly the same parent and daughter isotopes as the potassium-argon method, in effect, presenting a different way of telling time from the same clock. More accurate than the potassium-argon method, this method is less susceptible to parentless argon. The argon-argon method can determine if a system has been disturbed. In such cases rather than giving a wrong date, the rock gives no date.2

Rubidium-Strontium. In nearly all dating methods (except potassium-argon and argon-argon), some amount of the daughter product already exists in rocks when they cool. Using these methods is like trying to tell time with an hourglass that was turned over before all of the sand had fallen to the bottom. Good techniques exist to determine precisely how much of the daughter product resided in the rock when it began to cool and harden.

In the rubidium-strontium method, rubidium-87 decays to strontium-87. Several other isotopes in strontium are stable and do not decay. The ratio of strontium-87 to one of the stable isotopes, for instance strontium-86, increases over time as more rubidium-87 turns to strontium-87. But when the rock first cools, all parts of the rock have the same ratio of strontium-87/strontium-86 because the isotopes were well mixed in the liquid magma. Some of the minerals in the rock start out with a higher ratio of rubidium to strontium than others. Rubidium has a larger atomic size than strontium, so rubidium does not fit into the crystal structure of some minerals as well as others. Figure 3 presents an important concept used in rubidium-strontium dating.

Several things can, on rare occasions, cause problems for the rubidium-strontium dating method. If a rock contains some minerals that are older than the main part of the rock, dating can be difficult. Sometimes magma inside the earth picks up unmelted minerals from the surrounding rock as it moves through a magma chamber. Usually a geologist can distinguish these "xenoliths" from the younger minerals around them. If he or she does happen to use them for dating the rock, the points represented by these minerals reveal unreliability when plotted on a graph. Other difficulties arise if a rock has undergone metamorphism, that is, if the rock became very hot, but not hot enough to completely melt (or remelt). In these cases, the dates also appear as unreliable. Some of the minerals may have completely melted, while others did not melt at all, so thus some minerals express the igneous age while others minerals express the metamorphic age. In these cases no date is determined, as the different ages within the same rock appear inconsistent.

In rare instances, the rubidium-strontium method has given straight lines that produce wrong ages. This can happen when the rock being dated was formed from magma that was not well mixed, and which contained two distinct batches of rubidium and strontium. One magma batch had rubidium and strontium compositions near the upper end of a line (such as in figure 3), and one batch had compositions near the lower end of the line. In this case, the minerals got a mixture of these two batches, and their resulting composition ended up near a line between the two batches. This is called a two-component mixing line. Only about thirty cases of this mixing line have been documented among the tens of thousands of rubidium-strontium measurements made.

If a two-component mixture is suspected, a second dating method must be used to confirm or disprove the rubidium-strontium date. The agreement of several dating methods is the most fail-safe way of dating rocks. Researchers have made comparisons of numerous dating methods on the same rocks and have shown them in close agreement, even on very old samples.3

Many dating methods work similarly to the rubidium-strontium method. Some of the more common ones include samarium-neodymium, rhenium-osmium, and lutetium-hafnium. These methods all use three-isotope diagrams similar to figure 3 to determine the age. They differ from each other primarily in the types of minerals these element pairs prefer, in the length of their half-lives, and the measuring techniques they employ.

Uranium-Lead and Related Methods. The uranium-lead method, first used in 1907, is the longest-used dating method. More complicated than other parent-daughter systems, the uranium-lead system actually puts several dating methods together. Natural uranium consists primarily of two isotopes, U-235 and U-238, and these isotopes decay with different half-lives to produce lead-207 and lead-206, respectively. In addition, lead-208 is produced by thorium-232. Three independent estimates of the age of a rock can be ascertained by measuring the lead isotopes and their parent isotopes, uranium-235, uranium-238, and thorium-232. These are often used in combination to check for concordance, or agreement, between more than one chronometer.

Extinct Radionuclides: Hourglasses That Ran Out

After the sand has run down in an hourglass, the hourglass itself offers no way to determine how long ago it finished running down. In a similar manner, finding that a once abundant radioactive parent no longer exists indicates that a longer interval of time has elapsed than the one that isotope can help to measure. In this case, the parent isotope is said to be “extinct.”

A number of extinct isotopes have been identified by the measured presence of excessive amounts of the daughter isotope. These measurements show once abundant parent isotopes shortly after the creation of the solar system. Among these parents are calcium-41 (t1/2 = 130,000 years), aluminum-26 (700,000 years), iron-60 (1.5 million years), manganese-53 (3.7 million years), iodine-129 (16 million years), and plutonium-244 (82 million years). Extinct radioisotopes provide conclusive evidence that the solar system was created longer ago than the span of these half-lives.  Earth was created so long ago that radioactive isotopes with half-lives shorter than half a billion years have decayed away, but not so long ago that radioactive isotopes with much longer half-lives are gone.4 This scenario is equivalent to finding the sand still falling in an hour-measuring hourglass, while the sand in an “egg-timer” hourglass has run out.

Addressing the Challenges

Radiometric dating has proven reliable from relatively short timescales of seconds, minutes, days, and years (calibrated with laboratory clocks), to a few thousand years (cross-calibrated with other reliable age indicators), to many millions of years (cross-comparison performed between dating methods). Some people question whether data from so far in the past can be credible. But trusting dating methods is similar to trusting other events of history. Why do people believe Abraham Lincoln lived? An extremely elaborate scheme would be required to fabricate his existence, including forgeries, fake photos, false quotations, and many other things. In short, to believe he existed seems far more reasonable than to believe his existence was feigned. The situation with radiometric dating is similar, only examination of rock data rather than of historical records reveals the story. Multiple corroborations of radiometric dating make a very strong case for its validity.

  1. Radiometric dates agree with astronomical timescales.5 In astronomy, decay rate constancy can be tested easily by studying stars at varying distances. Since these distances represent different light travel times (hence different astronomical eras), astronomers can observe whether or not decay rates were slower or faster at different eras. Their research reveals constancy, and constancy confirms established radiometric dates.
  2. Vast amounts of evidence for the reliability of dating have appeared in periodicals such as Science, Nature, and specific geology journals. In 1999 alone, more than a thousand papers published on radiometric dating essentially agreed on a very old age for Earth.
  3. Most rocks are, for practical purposes, closed systems. Some doubters have tried to dismiss geologic dating by saying that no rocks are completely closed systems (i.e., rocks are not isolated from their surroundings and as a result have lost or gained some isotopes used for dating). From an extremely technical perspective this point may be true—perhaps one atom out of a trillion has leaked out of nearly all rocks—but such a change makes an unmeasurably small change in the result. Many books written over the past forty years detail the precise conditions under which dating mechanisms work.
  4. The presence of only two quantities in the exponent of the equation, half-life and time, make equations for radiometric decay extremely simple. No evidence in the past century suggests that decay rates might slow down over time, leading to incorrect dates. The following argument makes such an idea meaningless in terms of “apparent” but false ages: Based on the equation, in order for ages to appear longer than actual, all half-lives would have to change in sync with each other. Since different dating methods all produce agreement, all of the half-lives must have slowed. Such an occurrence would be as if time itself slowed down.
  5. A misconception exists that radiometric dating is based on index fossils with dates assigned long before radioactivity was discovered. In truth, radiometric dating is based on the half-lives of radioactive isotopes measured over the last forty to eighty years. Fossils do not calibrate them. Radiometric dating is most often used on igneous rocks while fossils are found in sedimentary rocks.
  6. Decay rates have been directly measured over the last fifty to eighty years. In some cases, a batch of pure parent material is weighed, then set aside for a long time. The resulting daughter material can then be weighed. Often, radioactive decays can be detected more easily by the energy bursts each decay gives off. For this detection, a batch of the pure parent material is carefully weighed and then put in front of a Geiger counter (or gamma-ray detector), which counts the number of decays over a long time period.
  7. If decay rates were poorly known, dates could be inaccurate. However, most decay rates used for dating rocks are known to within about 2 percent accuracy. Uncertainties are only slightly higher on rhenium (5%), lutetium (3%), and beryllium (3%).6 Such small uncertainties provide no reason to dismiss radiometric dating. Whether a rock is 100 million years old or 102 million years old makes little difference.
  8. Since exponents are used in the dating equations, some people believe that a small error in the half-lives could lead to very large errors in the dates. In reality, a half-life off by 2 percent, leads only to a 2 percent error in the date.
  9. Some individuals have suggested that a small change in the nuclear forces might have accelerated nuclear clocks during a certain period just a few thousand years ago, causing spuriously old radiometric dates. Since methods date rocks from the time of their formation, such a change of nuclear forces would have to have occurred after Earth (and the rocks) were formed. To make a difference, the half-lives would require shortening from several billion years down to several thousand years—a factor of at least a million. Such a shortening would cause large physical effects. For example, Earth is heated substantially by radioactive decay. If that decay is sped up by a factor of a million or so, the tremendous heat pulse would easily melt the whole planet, including the rocks in question. 
  10. Some people suggest that the “full-life” (the time at which all of the parent is gone) should be measured rather than the half-life (the time when half of it is gone). Unlike sand in an hourglass, which drops at a constant rate independent of how much is remaining, the number of radioactive decays is proportional to the amount of parent remaining. Figure 2 shows how after two half-lives, ½ x ½ = ¼ is left, and so on. After 10 half-lives there is 2-10 = 0.098% remaining. Scientists sometimes instead use the term “mean life,” that is, the average life of a parent atom. The mean life is always 1/ln(2) = 1.44 times the half-life. Most people more easily understand half-life.
  11. Subjecting rocks used in dating methods to heat, cold, pressure, vacuum, acceleration, and strong chemical reactions that could be experienced on Earth or other planets yields no significant change in radioactive decay rates.
  12. Claims of unreliability have been made based on the inaccurate dating of a rock from the Mount Saint Helens eruption (1980). The dating lab reported it as several million years old. Does this mean radiometric dating can't be trusted? Not when proper procedures are observed. Radiometric dating can be "tricked" if a single dating method is improperly used on a sample. Anyone can move the hands on a clock to indicate the time incorrectly. Likewise, people actively looking for incorrect radiometric dates can find them. However, multiple dating methods used together on igneous rocks are typically trustworthy.

  13. Some people propose that since radiogenic helium and argon continue to escape from Earth’s interior, Earth must be young. However, the radioactive parent isotopes, uranium and potassium, have very long half-lives, as shown in Table 1. These parents still exist and still produce helium and argon in abundance in Earth’s interior. Further, a time lag exists between the production of daughter products and their escape (or degassing). If Earth were geologically young, very little helium and argon would have been produced by now. What does the evidence show? Researchers have compared the amount of argon in the atmosphere to the amount expected from decay of potassium over 4.6 billion years, and they find consistency.

  14. Unsubstantiated speculation can produce the idea that only nontheists and others who dismiss the inerrancy of the Bible give credence to radiometric dating techniques. However, the roots of the scientific age can be traced to the idea that God’s creation is testable, trustable, and worthy of systematic study. The key concept of such study details God’s revelation of Himself, not only through the Bible (special revelation) but also through creation (general revelation). A great number of other Christians recognize with conviction that radiometric dating substantiates evidence that God created Earth billions, not thousands, of years ago. Many Christians work in the field of radiometric dating.

God’s Word Validates Scientific Conclusions

Accepting the reliability of radiometric dating cannot be considered equivalent to compromising the spiritual and historical inerrancy of God’s word. Many Christians view a proper reading of Genesis 1 to indicate that “day” refers literally to a long period of time.

The psalmist marveled at the scope of God’s creation. Today, the length and breadth of God’s creation, both in temporal and spatial dimensions, speak ever more clearly of the Creator’s awesome nature. The heavens do declare the Lord’s glory, and the Earth indeed shows God’s handiwork. Radiometric dating testifies to the magnificence of God’s power. Careful consideration of all the scientific facts and all the relevant Scripture passages can help people like Janet discern both the age of Earth and the validity of the biblical creation account. Together science and Scripture provide the answer Janet needs for herself—and for her son.

Roger C. Wiens wrote his Ph.D. dissertation on isotope ratios in meteorites. He worked for ten years in the geology departments at Caltech and the University of California, San Diego, characterizing oceanic rocks and isotope ratios in diamonds, and studying the feasibility of a space mission for NASA. He presently works in the Space and Atmospheric Sciences Department of the Los Alamos National Laboratory. He has published over 20 scientific research papers and has also published articles in Christian magazines. Dr. Wiens has been a member of Mennonite, Baptist, and Conservative Congregational churches.

Glossary:

  • Atom: The smallest unit that materials can be divided into. An atom is about ten billionths of an inch in diameter and consists of a nucleus of nucleons (protons and neutrons) surrounded by electrons.
  • Closed system: A system (rock, planet, etc.) that has no influence or exchange with the outside world. In reality there is always some exchange or influence, but if this amount is completely insignificant for the process under consideration (e.g., for dating, if the loss or gain of atoms is insignificant) for practical purposes the system can be considered closed.
  • Daughter: The element or isotope that is produced by radioactive decay.
  • Decay: The change from one element or isotope to another. Only certain isotopes decay. The rest are said to be stable.
  • Element: A substance that has a certain number of protons in the nucleus and unique properties. Elements may be further broken down into isotopes, which have nearly all of the same properties except for their mass and their radioactive decay characteristics.
  • Half-life: The amount of time it takes for half the atoms of a radioactive isotope to decay.
  • Igneous rock: Rock formed from molten lava. The other two types of rock are sedimentary (formed by the cementing together of soil or sand) and metamorphic (rocks re-formed by heat over long periods of time).
  • Isotope: Atoms of a given element that have the same atomic number. Most elements have more than one isotope. Most radioactive elements used for dating have one radioactive isotope and at least one stable isotope. For example carbon-14 (which weighs 14 atomic mass units) is radioactive, while the more common isotopes, carbon-12 and carbon-13 are not.
  • Magma: Hot molten material from which rocks are formed. When magma erupts on the surface of the earth it is called lava.
  • Metamorphism: The heating of rocks over long time periods at temperatures which are hot enough to change the crystal structure but not hot enough to completely melt the rock. Metamorphism tends to alter or reset the radiometric time clocks, though some radiometric techniques are more resistant to resetting than others.
  • Nucleons: Neutrons and protons, which make up the nucleus of an atom.
  • Parent: The element or isotope which decays. The element it produces is called the daughter.
  • Radioactive: Subject to change from one element to another. During the change, or decay, energy is released either in the form of light or energetic particles.
  • Radiocarbon: Carbon-14, which is used to date dead plant and animal matter. Radiocarbon is not used for dating rocks.
  • Radiometric dating: Determination of a time interval (e.g., the time since formation of a rock) by means of the radioactive decay of its material. Radiometric dating is one subset of the many dating methods used in geology.
  • Three-isotope plot:  In dating, this is a plot in which one axis represents the parent isotope and the other axis represents the daughter isotope. Both parent and daughter isotopes are ratioed to a daughter element isotope that is not produced by radioactive decay. This type of plot gives the age independent of the original amounts of the isotopes.
  • Two-component mixing: The mixing of two different source materials to produce a rock. On rare occasions this can result in an incorrect age for certain techniques that use three-isotope plots. Two-component mixing can be recognized if more than one dating technique is used, or if surrounding rocks are dated.
  • Xenolith: Literally, a foreign chunk of rock within a rock. Some rocks contain pieces of older rocks within them. These pieces were ripped off of the magma chamber in which the main rock formed and were incorporated into the rock without melting. Xenoliths do not occur in most rocks, and they are usually recognizable by eye where they do occur. If unrecognized, they can result in an incorrect date for a rock (the date may be of the older xenolith).

References:

  1. Norman E. Holden, “Total Half-Lives for Selected Nuclides,” Pure Applied Chemistry 62 (1990), 941-58. See also geochronology textbooks such as Alan P. Dickin, Radiogenic Isotope Geology (New York: Cambridge Press, 1995); Gunter Faure, Principles of Isotope Geology, 2d ed. (New York: Wiley, 1986).
  2. 2. Roger C. Wiens, Radiometric Dating: A Christian Perspective, available from ASA Web site (1995) http://www.asa3.org/ASA/resources/Wiens.html; Internet; accessed 8/01/01. See also geochronology textbooks such as those by Dickin; Faure.
  3. Wiens; G. Brent Dalrymple, The Age of the Earth (Stanford, CA: Stanford University Press, 1991).
  4. Some isotopes with half-lives shorter than several hundred million years exist, but only because they are constantly being replenished by either cosmic rays (a special case, e.g., the three lowest entries in Table 1) or because they themselves are daughters of some longer-lived parent such as uranium.
  5. Hugh Ross, Creation and Time, (Colorado Springs, CO: NavPress, 1994).
  6. Holden, 941-58; see also geochronology textbooks such as Dickin; Faure.

  7. Half lives taken from Holden, 941-58; see also geochronology textbooks such as Dickin; Faure.
    Figure Captions

Table I.

Parent-daughter pairs and half-lives for some of the most commonly used radiometric dating methods.7

Radioactive

Isotope

(“Parent”)

Decay Product

(“Daughter”)

Half-Life

(Years)

Samarium-147 Neodymium-143 106 billion
Rubidium-87 Strontium-87 48.8 billion
Rhenium-187 Osmium-187 42 billion
Lutetium-176 Hafnium-176 38 billion
Thorium-232 Lead-208 14 billion
Uranium-238 Lead-206 4.5 billion
Potassium-40 Argon-40 1.26 billion
Uranium-235 Lead-207 0.7 billion
Beryllium-10 Boron-10 1.52 million
Chlorine-36 Argon-36 300,000
Carbon-14 Nitrogen-14     5,715

Sidebar: Atoms, Isotopes, and Radioactive Decay

By Fazale Rana, Ph.D.

Atoms, the smallest, chemically distinct units of matter, are roughly 0.1 to 0.2 nm in size (one nanometer is one-billionth of a meter). Three elementary particles make up atoms. Two of them, protons and neutrons, interact to form the atom’s nucleus. A cloud of electrons surrounds the nucleus. Essentially all of an atom’s volume comes from its electron cloud, whereas nearly all of the atom’s weight resides in the protons and neutrons in its nucleus.

Protons possess a unit positive charge, while neutrons contain no charge. This renders the nucleus with a positive charge equal to the number of protons resident in the nucleus. Electrons possess a negative charge. For an atom to maintain electrical neutrality, the number of its electrons must equal the number of its protons.

The number and arrangement of electrons surrounding the nucleus determines the atom’s chemistry. Since the electronic structure of an atom depends on the number of its protons, that proton number (atomic number) defines the atom. Any atom with 19 protons, for example, is a potassium atom; any atom with 37 protons is a rubidium atom, and any atom with 38 protons is a strontium atom. The number of protons and neutrons determines the atom’s mass (atomic mass).

While the proton number must remain fixed for a particular type of atom, the number of neutrons may vary. Variation in neutron number does not change the chemistry of the atom, but does change the atomic weight. For example, potassium-39 has 19 protons and 20 neutrons; potassium-40 has 19 protons and 21 neutrons. Both potassium-39 and potassium-40 display identical chemical properties, since they both have 19 protons. Potassium-40 weighs more than potassium-39 by 1 atomic mass unit (amu), since it has one more neutron in its nucleus than potassium-39.

Atoms with the identical number of protons but possessing a differing number of neutrons are called isotopes. Potassium-39 and potassium-40 are both isotopes of potassium.

Certain proton and neutron number combinations are unstable. When this instability occurs, the nucleus breaks down through the process of radioactive decay to a stable combination of protons and neutrons. In this decay process, the (parent) atom’s nucleus either gains or loses protons. This results in the formation of a new (daughter) atom. For example, potassium-40’s nucleus is unstable. As a result, the potassium-40 nucleus picks up an electron from the surrounding electron cloud. This electron combines with a proton to form a neutron. The resulting nucleus gains a neutron and loses a proton. Since the total number of protons plus neutrons defines the atom’s mass, the atomic mass remains unchanged, but the atomic number decreases by one. The newly formed daughter atom possesses 18 protons, 18 electrons and 22 neutrons. Any atom with 18 protons is an argon atom. This transformation, or “radioactive decay'” process, alters the chemical properties of the parent potassium atom producing a daughter atom of argon, a gas.

Exotic Life Sites: The Feasibility of Far-Out Habitats

By Hugh Ross

(Spanish Version)

People often joke about the certainty of death and taxes. Astronomers can add another certainty to that short list: Sooner or later someone will ask, “What do you think about the possibility of life out there?”

Most questioners are looking for a particular answer. Science fiction novels, The Planetary Society, and countless movies, from E.T. to Contact to Planet of the Apes, suggest that extraterrestrial life is a given and help conjure images of how that life looks. To answer questions about such life takes as much diplomacy as answering my wife when she asks, “How do I look?”

Experience suggests a strategy for handling both questions. Step one: Make a positive statement, such as “You look great!” or “That’s a great question!” Step two: Provide amplification. This part is trickier. It can make or break the interaction. If it lacks sincerity or includes the word but, (e.g., “You look great, but I thought you were going to wear the blue dress”), my wife may walk away feeling hurt and deflated. A better answer adds some specific feedback (e.g., “You look great, and I especially like the way that color goes with your eyes”).

In the case of the life-elsewhere question, an honest, fact-based amplification acknowledges the “great question” as opening the door to three fascinating topics: life on other planets, life on other astronomical bodies, and life other than “life as we know it.” Step-by-step discussion of these subjects can lead to opportunities for spiritually significant conversation.

Life on Other Planets

Technology and interdisciplinary research have enabled scientists to develop an extensive list of physical characteristics that must fall within limited ranges for a planet (or any other astronomical body) to be capable of life support. Those characteristics involve the planet’s star, moon(s), planetary companions, and galaxy, as well as the planet’s surface, interior, and atmospheric conditions. This list grows longer with every year. It started with two parameters in 1966,1 grew to eight by 1970, to twenty-three by 1980, to thirty by 1990, and to forty by 1995.2 Currently, the list includes more than 120 parameters and shows no signs of leveling off.3

The limits on some characteristics, especially on the essential-to-life features of a planet’s star, have been determined precisely. The limits on others, mostly on the features of the planet itself, presumably a terrestrial (rocky) planet, are less precisely known. Two reasons exist for this difference: First, trillions of stars are available for study while only 76 planets (9 in Earth’s solar system, 67 outside) have been discovered to date. Second, physical and chemical characteristics make stars, basically condensed balls of hot gas, much simpler systems than planets.

No one knows, of course, exactly how many planets exist. As recently as 1990, astronomers were divided between those who proposed that planets whirl around nearly every star and those who posited that the Sun alone possesses planets. Three research advances tilt the debate toward the latter scenario: (1) the availability of instruments and techniques capable of detecting and studying planets orbiting other stars; (2) the discovery that most, if not all, stars surrounded by disks of dust are young or still forming; and (3) the development of sophisticated theoretical models that explain how dust disks become planets. 

Each of the 67 extrasolar planets discovered and studied to date orbits a relatively young, metal-rich star (a star rich in elements heavier than hydrogen and helium).4-8 This finding presents no surprise. The heavy elements needed to make planets and any type of life chemistry do not exist in sufficient quantity until at least two generations of stars have formed, burned out, and scattered their ashes, which then recycle to form more stars. Astronomers have learned that the longer a galaxy sustains star formation, the more metal rich its newly forming stars will be. In the case of the galaxy astronomers know best, the Milky Way galaxy (Earth’s own), only 2 percent of the stars possess metal richness adequate for planet formation.9

Of those Milky Way stars known to have planets, none formed as early as the Sun. The Sun benefited from a remarkable set of circumstances: it formed adjacent to two massive, star explosions (supernovae), each of which spewed out a different set of life-essential heavy elements.10-12 Those explosions occurred precisely at the right time and place for those heavy elements to be incorporated into the condensing solar nebula. Earth’s star may be the only star its age with an ensemble of both small rocky planets and gas giants. This finding implies that the probable number of life-site candidates falls far below 2 percent.

As for life-support planets in other galaxies, the odds look bleak. Astronomers have found that the Milky Way is exceptional for the longevity of its star formation processes. In 94 of every 100 galaxies, star formation shut down so long ago that few, if any, metal-rich stars reside there—hence few, if any, planets. The results of a Hubble Space Telescope (HST) study recently confirmed this conclusion. The HST searched for planets in an enormous cluster of old stars, 47 Tucanae, and found none.13

Observations indicate that the number of stars with planets, any kind or size of planets, adds up to only about 0.1 percent of all the stars in the cosmos. That number is at least a hundred times smaller than the estimate that launched the search for signals from extraterrestrial life.14 Small though that percentage may be, however, it still adds up to a lot of planets. If, for example, each star in that 0.1-percent group has ten planets around it, the number of planets would add up to a hundred million trillion (that is, 1020).

A hundred million trillion, then, is the number to which the data on various life-essential features must be applied. Some features fall within loose limits—others, within strict limits. Limits on the planet’s rotation period and its albedo (reflectivity) eliminate about 90 percent of the life-site candidates. Parameters such as the parent star’s mass and the planet’s distance from its parent star eliminate about 99.9 percent of all relevant candidates.

Dependency factors among certain of the parameters improve the odds somewhat, but many of these parameters must be kept within a specific range for long periods of time. Given how variable environments can be, this longevity requirement proves extremely limiting. The data demonstrate that the probability of finding even one planet with the capacity to support life falls short of one chance in 10140 (that number is 1 followed by 140 zeros).15

Life on Alternative Sites

The extreme improbability such a number indicates has driven some scientists to abandon the premise that life requires an Earth-like home. A satellite (moon) orbiting a giant planet that in turn orbits a star resembling Earth’s sun at the right distance could serve, they say, as a life site.16-18 The feasibility of such an alternative can be tested against a long list of recent findings.

None of the 67 “gas giant” planets found thus far outside Earth’s solar system orbit their stars in the zone life requires. Gas giants, which are many times larger than Earth, form under cold, low radiation conditions far from their stars. By gravitational interactions with interplanetary dust or with other planets and stars that pass by, most gas giants drift into the proximity of their stars. This drifting process drastically decreases their likelihood of retaining the nearly circular, stable orbit life demands.19-24 Of the known extrasolar gas giants, only two orbit anywhere near the life-habitable zone, and these two follow such an eccentric (i.e., elongated) orbital path as to make life on their satellites (moons), if they have any, impossible.25-28 The question remains unanswered as to whether or not giant planets can possibly retain the satellites during migration.

A satellite close enough to its planet to avoid enormous seasonal temperature fluctuations (caused by variations in the distance to the planet’s star, or heat source, as the satellite orbits its planet) becomes tidally locked to the planet—the same side always faces the planet. This tidal locking itself causes a host of life-destructive effects.

For example, tidal locking makes the satellite’s rotation period identical to the planet’s. Unless that period is short enough, day-to-night temperature differences become too extreme for life’s survival. However, the rotation period can only be that short if the satellite orbits closely. Within this sufficiently close range, however, another set of problems arises. For example, tidal forces generate drastic climatic and orbital instabilities (tidal torques force such a satellite to move farther and farther away from its planet), as well as massive and frequent volcanic eruptions (such as astronomers see on Jupiter’s moon Io).29 Any possible life-favorable conditions last briefly, at best.

A satellite with a highly improbable life-sustaining atmosphere most likely loses it in short order unless that satellite somehow possesses a strong magnetic field (similar to that of the Sun, Jupiter, and Earth). Otherwise, charged particles accelerated by the planet’s magnetosphere sputter away the satellite’s atmosphere. The magnetic field around Ganymede, the largest known planetary satellite and the only one with undisputed magnetism, measures less than 1 percent the strength of Earth’s.30-32

Another life risk for a satellite closely orbiting a large planet is that such a planet’s gravity significantly attracts asteroids, comets, and other debris passing nearby. This attraction increases the likelihood of bombardment, and such bombardment proves catastrophic to any possible life on the satellite.

A satellite cannot retain an adequate atmosphere for life unless its mass exceeds 12 percent of Earth’s mass. 33 At the same time, the satellite needs a mechanism to compensate for its nearby star’s increasing luminosity (brightness, thus light and heat radiation) as the star ages. The only known mechanism is the one seen on Earth, called the carbonate-silicate cycle. This cycle cannot operate, however, without lots of dry land (which eliminates ice-water environments such as Jupiter’s satellite Europa) and without a high level of plate tectonic activity.34, 35

Plate tectonics, in turn, require a certain minimum mass (0.23 Earth masses), and the demands of sustaining a carbonate-silicate cycle significantly increases that minimum. The best calculation to date sets the minimum mass of this hypothetical satellite at three times the mass of Mars, which is more than twelve times the mass of the solar system’s largest satellite. Of course plate tectonics also demand lots of liquid water (thus eliminating all dry satellites) and the precisely-timed introduction of just-right plant life in just-right amounts throughout the satellite’s history.36-37

More Radical Proposals

Sustaining the quest for other potential life sites, planetary scientist David Stevenson and origin-of-life researchers Jeffrey Bada and Christopher Wills go so far as to speculate that life might not require a home near a star.38-39 They suggest this scenario: A planet may be ejected from a normal planetary system before losing any of its light gases. If so, the planet may retain enough surface warmth (from interior radioactive decay) and a sufficiently heavy molecular hydrogen outer atmosphere (a heat-trapping blanket) to sustain life chemistry and metabolism. 

To be capable of life support, however, such a hypothetical site would require super-enrichment by radioactive elements, and no mechanism or scenario exists to bring this enrichment about—none that would accomplish the job without simultaneously destroying the molecular hydrogen outer atmosphere. If the planet somehow acquired this enrichment, it still faces a problem: heat from the radioactive decay would decline exponentially through time. So, while such a planet might serve as a brief stopover for primitive life, it could not stay within the life-support range of temperature and other conditions long enough to serve as any conceivable home for intelligent life.

If life claims a home anywhere in the vast cosmos, it must be on a planet like Earth orbiting a star like the Sun in a galaxy like the Milky Way. And, as ongoing studies shows, that possibility shrinks, rather than grows, as each year’s research adds to the harvest of data. Extraterrestrial life does indeed appear to be homeless—unless, of course, a transcendent, supernatural Being built that home. But that possibility points toward, rather than away from, belief in the biblical Creator.

Alternative Life Forms

One other possibility must still be addressed, a question that often hampers progress toward a realistic assessment of the chance for life elsewhere: To what degree might extraterrestrial life differ from “life as we know it”? At one time biologists speculated that extraterrestrial life might be based on exotic chemistry, something other than carbon.

So, biochemists went to work on the problem. Their research showed that only silicon and boron, besides carbon, can serve as the basis for adequately complex molecules—molecules capable of sustaining basic life functions, such as self-replication, metabolism, and information storage. This finding presents some significant problems, however. First, silicon can hold together a string of no more than a hundred amino acids—far too short a string to accommodate any conceivable life systems and processes. Second, throughout the universe boron is less abundant than carbon; so carbon always supersedes it. Third, concentrated boron is toxic to certain life-critical reactions.

The conclusion, published as early as 1961, still stands. Physicist Robert Dicke deduced at that time that if anyone wants physicists (or any other physical life forms, for that matter), carbon-based biochemistry is a must.40 The key word, here, is physical. What about life that is not physical?

The Spiritual Opportunity

Both science and the Bible offer helpful information on this topic of non-physical reality. Science points to the existence of a transcendent (beyond space and time), personal Creator, demonstrably the same Creator revealed in the pages of Scripture. The Bible, in turn, reveals the existence of life forms other than Earth life, other than physical life. This life may be described as spiritual life, and yet it possesses the capacity for at least some physical expression or manifestation.

The Bible calls these creatures (in English translations) “angels,” “ministering servants,” or “ministering spirits.” Three specific names are given in the text: Michael, Gabriel, and Lucifer. The latter, also called Satan, led a rebellion against God. Scripture refers to the angels who rebelled with him (about a third of the total number) as “evil spirits,” “devils,” or “demons.” The one reliable source of information about this other kind of life is the Bible, and further study is highly recommended.

The possibility for life elsewhere is in fact great, as great as the certainty that the Bible is a true, trustworthy, and relevant revelation from the Creator. Any question that leads to an opportunity to talk about the word of God as well as the work of God, the Creator, deserves to be called a great question. 

References:

  1. Iosef S. Shklovskii and Carl Sagan, Intelligent Life in the Universe (San Francisco: Holden-Day, 1966), 343-52.
  2. Hugh Ross, The Creator and the Cosmos, 2d ed. (Colorado Springs, CO: NavPress, 1995), 132-44.
  3. Hugh Ross, The Creator and the Cosmos, 3d ed. (Colorado Springs, CO: NavPress, 2001), 195-99.
  4. Guillermo Gonzalez, “The Stellar Metallicity-Giant Planet Connection,” Monthly Notices of the Royal Astronomical Society 285 (1997): 403-12.
  5. Guillermo Gonzalez, “Spectroscopic Analysis of the Parent Stars of Extrasolar Planetary System Candidates,” Astronomy and Astrophysics 334 (1998): 221-38.
  6. Guillermo Gonzalez, George Wallerstein, and Steven H. Saar, “Parent Stars of Extrasolar Planets. IV. 14 Herculis, HD 187123, and HD 210277,” Astrophysical Journal Letters 511 (1999): L111-14.
  7. Guillermo Gonzalez and Chris Laws, “Parent Stars of Extrasolar Planets. V. HD 75289,” Astronomical Journal 119 (2000): 390-96.
  8. Guillermo Gonzalez et al., “Parent Stars of Extrasolar Planets. VI. Abundance Analyses of 20 New Systems,” Astronomical Journal 121 (2001): 432-52.
  9. Guillermo Gonzalez, private communication, 1991. The 2 percent figure was determined from the minimum metal richness observed in stars with planets and the maximum age of stars with planets. Interestingly, Carl Sagan came up with the same figure in 1966 (Shklovskii and Sagan, 344).
  10. S. Sahipal et al., “A Stellar Origin for the Short-Lived Nuclides in the Early Solar System,” Nature 391 (1998), 559-661.
  11. G. J. Wasserburg, R. Gallino, and M. Busso, “A Test of the Supernova Trigger Hypothesis with 60Fe and 26Al,” Astrophysical Journal Letters 500 (1998): L189-93.
  12. Peter Hoppe et al., “Type II Supernova Matter in a Silicon Carbide Grain from the Murchison Meteorite,” Science 272 (1996): 1314-16.
  13. Ronald L. Gilliland et al., “A Lack of Planets in 47 Tucanae from a Hubble Space Telescope Search,” Astrophysical Journal Letters 545 (2000): L47-51.
  14. Shklovskii and Sagan, 343-50.
  15. Ross, The Creator and the Cosmos, 3d, 187-99.
  16. J. F. Kasting, D. P. Whitmire, and R. T. Reynolds, “Habitable Zones around Main Sequence Stars,” Icarus 101 (1993): 108-28.
  17. Darren M. Williams, James F. Kasting, and Richard Wade, “Habitable Moons around Extrasolar Giant Planets,” Nature 385 (January 1997), 234-36.
  18. Darren M. Williams, “Habitable Moons around Extrasolar Giant Planets,” in The Stability of Habitable Planetary Environments (Ph.D. thesis, Pennsylvania State University, 1998), 111-20.
  19. Frederic A. Rasio and Eric B. Ford, “Dynamical Instabilities and the Formation of Extrasolar Planetary Systems,” Science 274 (November 1996): 954-58.
  20. N. Murray, B. Hansen, M. Holman, and S. Tremaine, “Migrating Planets,” Science 279 (January 1998): 69-72.
  21. D. N. C. Lin, P. Bodenheimer, and D. C. Richardson, “Orbital Migration of the Planetary Companion of 51 Pegasi to Its Present Location,” Nature 380 (April 1996), 606-7.
  22. Stuart J. Widenschilling and Francesco Marsari, “Gravitational Scattering as a Possible Origin for Giant Planets at Small Stellar Distances,” Nature 384 (December 1996), 619-21.
  23. Stuart Ross Taylor, Destiny or Chance: Our Solar System and Its Place in the Cosmos (Cambridge, UK: Cambridge University Press, 1998).
  24. Jean Schneider, Extra Solar Planets Catalog www.obspm.fr/encycl/catalog.html.
  25. S. Vogt et al., “Six New Planets from the Keck Precision Velocity Survey,” Astrophysical Journal 536 (2000): 902-14.
  26. Gozalez, Wallerstein, and Saar, L111-14.
  27. Ing-Guey Jiang and Wing-Huen Ip, “The Planetary System of Upsilon Andromedae,” Astronomy and Astrophysics 367 (2001): 943-48.
  28. Jean Schneider, Extra Solar Planets Catalog. wwwusr.obspm.fr/departement/darc/planets/encycl.html.
  29. William B. McKinnon, “Galileo at Jupiter—Meetings with Remarkable Moons,” Nature 391 (1997), 23-26.
  30. Guillermo Gonzalez, “New Planets Hurt Chances for ETI,” Facts & Faith 12, no. 4 (1998), 2-4.
  31. D. A. Gurnett et al., “Evidence for a Magnetosphere at Ganymede from Plasma-wave Observations by the Galileo Spacecraft,” Nature 384 (December 1996), 535-37.
  32. M. G. Kivelson et al., “Discovery of Ganymede’s Magnetic Field by the Galileo Spacecraft,” Nature 384 (December 1996), 537-41.
  33. Kivelson et al., 541.
  34. Hugh Ross, The Creator and the Cosmos, 3d ed. (Colorado Springs, CO: NavPress, 2001), 180-83.
  35. Darren M. Williams, thesis, 115-17.
  36. Katherine L. Moulton and Robert A. Berner, “Quantification of the Effect of Plants on Weathering: Studies in Iceland,” Geology 26 (October, 1998): 895-98.
  37. Tyler Volk and David Schwartzman, “Biotic Enhancement of Weathering and the Habitability of Earth,” Nature 340 (1989), 457-60.
  38. David Stevenson, “Life-Sustaining Planets in Interstellar Space?” Nature 400 (1999), 32.
  39. Christopher Wills and Jeffrey Bada, The Spark of Life (Cambridge, MA: Perseus Publishing, 2000), 250-52.
  40. Robert H. Dicke, “Dirac’s Cosmology and Mach’s Principle,” Nature 192 (1961), 440.

The Leap to Two Feet: The Sudden Appearance of Bipedalism

By Fazale R. Rana

(Spanish Version)

Did man crawl his way into existence over millions of years? Or did he leap to two feet by supernatural design? Did humans emerge from amoebas or did a Creator intend for life to possess purpose, value, and meaning? Answers to such questions mightily impact how human societies respond to their most pressing problems. A divinely-designed, sentient, spiritual creature deserves greater care and consideration than does a random fluke of nature.

Some scientists say that human beings are a mere quirk of fate—intelligent apes produced by chance events taking place over the last 5 million years. They claim natural selection played a role in the process that led to modern humans. Competitive, predatory, and environmental pressures gradually selected inheritable changes, they say. These changes supposedly imparted increased survivability and reproductive success. Thus, natural selection would have operated on random variation again and again, producing a succession of new species until finally by chance modern humans came to be.

Along with large brain size (actually, brain size-to-body mass ratio), manual dexterity, and advanced culture, bipedalism constitutes one of the most important defining characteristics of humans. For evolutionary anthropologists, understanding the emergence and development of bipedalism equates with understanding the origin of humanity.

In sharp contrast to evolutionary thinking, the Bible reveals human beings as the pinnacle of God’s creative activity, made in His image and distinct from all other creatures.1 Biblical accounts of man’s beginnings leave no room for God’s using an ape-to-human evolutionary transformation process to create man. Scripture describes God’s direct involvement in creating the first humans, physical and spiritual creatures of immense worth from the time of their inception.

With its focus on testability,2 a powerful new approach helps discriminate between the biblical and evolutionary explanations for the origin of humanity (see sidebars). Predictions made by these origin models can be subjected to the rigors of scientific testing. The one with the greatest support from the scientific record and with predictions that best accommodate new discoveries exemplifies the most accurate scenario.

Recent advances in paleoanthropology (the study of the bipedal primate fossil record) and the paleoecology (study of ancient ecologies) associated with bipedalism present an unusual opportunity to make data comparisons. New discoveries in these, as well as other disciplines, argue against a naturalistic origin to bipedalism and provide substantial affirmation for the biblical record.

Evolutionary Scenarios

According to the evolutionary paradigm, since an ape-like ancestor gave rise to both the ape and the human lineages, bipedal primates must have evolved from knuckle-walking quadrupeds. Knuckle-walking exists as a special type of terrestrial quadrupedalism (ground-based locomotion employing all four limbs) possessed by chimpanzees and gorillas.3 Knuckle-walkers rest their weight on their knuckles, not on their palms or fingers. This design allows chimpanzees and gorillas to walk on all four limbs while still having the dexterity of long curved fingers for climbing and swinging through trees.

Paleoanthropologists propose a myriad of hypotheses to explain how bipedalism could arise from natural processes. One early explanation suggests bipedalism emerged to free the hands for tool use. Since the fossil record contradicts this notion, evolutionary biologists have rejected this idea. The archeological record clearly shows the existence of bipedalism at least 2 million years before tool use appeared.4

Most hypotheses seeking to account for bipedalism’s emergence depend on East Africa’s transformation from a woodland and forest environment to an arid, open savanna.5 With such changes, terrestrial quadrupeds faced reduced food supplies, increased risk of falling prey to predators, and the inability to avoid direct sunlight.6

Bipedalism offers a way to address these challenges. Walking erect served as a more energy efficient means of locomotion at slow speeds.7 This allowed bipedal primates to traverse long distances foraging for food. Once having found food, bipedal primates could carry the foraged food long distances as they returned to their “home-base” to provide for their young.8

By the height of their heads, bipedal primates are more effective at avoiding predation in an open savanna than quadrupedal apes. Standing erect would allow these animals to detect predators sooner and from greater distances.

Bipedalism also offers a thermoregulatory advantage.9 A bipedal primate standing upright absorbs 60 percent less heat than does an ape walking on all four limbs. A quadrupedal stance exposes the entire back to direct sunlight, whereas standing erect exposes only the head and shoulders.

Evolutionary biologists have yet to reach a consensus on the selective pressures that could have produced bipedalism in primates, nor have they demonstrated a mechanism that can bring about such dramatic changes in the time permitted (see the following section). To date, the only reasonable source of evolutionary pressure behind the four-to-two transformation remains the loss of a woodland habitat throughout East Africa. 

Anatomy of Bipedalism

To transition from a knuckle-walking quadruped to an upright biped involves extensive anatomical changes.10 These changes include the following:

  • Relocation of the spinal cord opening
    The foramen magnum (the opening in the base of the skull that receives the spinal cord) must be relocated from the back to the center of the skull base. In this position the vertebral column effectively balances the head, eliminating the need for powerful neck muscles.
  • Restructuring of the inner ear bones
    The inner ear bones, which play a role in balance, must be altered to support bipedalism.
  • Introduction of spinal curvature
    The lower and upper vertebral column must possess forward curvature to maintain bipedalism. This forward curvature coupled with the backward curvature in the middle of the spinal column allows the backbone to function as a spring, facilitating movement.
  • Restructuring of the rib cage
    Apes’ inverted funnel-shaped rib cage accommodates arm use for locomotion. The barrel-shaped rib cage of bipeds permits effective use of the arms for nonlocomotory functions.
  • Reshaping the pelvis
    To accommodate the hip joints and muscles necessary for bipedalism, the pelvis of bipedal primates must be lower and broader than that of knuckle-walking apes.
  • Altered lower limbs
    Bipedal primates not only have longer lower limbs than quadrupeds, the valgus angle (the angle that the femur makes with the midline of the body) is also different. Longer lower limbs shift the center of mass towards the lower body. Angling the femurs inward moves the center of mass closer to the midline of the body. The altered center of mass allows stable bipedal locomotion.
  • Enlarged joint surfaces
    Not only does the knee need to be restructured to accommodate the changed valgus angle, but joint surfaces must also be enlarged. This enlargement increases the contact area, helping the knee and other joints withstand the stress of standing or walking upright.
  • Restructured foot
    Even the feet must be structured differently to support bipedalism. A platform foot with an arch allows for a greater surface area, one that can better withstand shock. In bipedal primates, the big toe is more elongated and aligned with the other toes and, thus, needs a different location. This new placement allows the toe to make the last point of contact with the ground as the leg swings forward during a bipedal stride.
  • Restructuring of the body’s musculature
    In order to accommodate the extensive skeletal changes required by the transition from a quadruped to a biped, much of the musculature must also be altered.

Predictions

The dramatic anatomical changes that must occur to transform knuckle-walking quadrupeds to bipedal primates thwart efforts to envision how this transformation could take place. Nevertheless, if bipedalism did emerge through natural-process biological evolution, it should occur gradually and appear well after the time that apes and humans are supposed to have diverged. Moreover, the first form of bipedalism to appear should be crude and inefficient. Once appearing, it should gradually transition to the more efficient obligatory bipedalism of modern humans. Lastly, significant evolutionary pressure would be necessary to force knuckle-walking apes, perfectly suited for their environment and lifestyle, to change into upright walking primates, if such change actually could occur.

Recent Scientific Advances

Several recent discoveries from the fossil and geological records have radically transformed paleoanthropologists’ view of the origin and natural history of bipedalism. These new scientific advances sharply contradict predictions stemming from evolutionary scenarios.

Bipedalism’s First Appearance

In 1994 and 1995 paleoanthropologists reported two sets of discoveries that described the fossil remains of two species of australopithecines. One research team uncovered the remains of a hominid in Ethiopia dated at 4.4 million years in age.11 This specimen they named Australopithecus ramidus, though it was later reassigned to a new genus, Ardipithecus.12

Meanwhile, another team of researchers discovered a set of hominid fossils in Kenya determined to be between 3.9 and 4.2 million years in age.13 These specimens were attributed to a newly recognized australopithecine species, Australopithecus anamensis. A follow-up discovery confirmed the date for this species at 4.07 million years ago.14 Analysis of an A. anamensis tibia clearly established its bipedal capacity, pushing the appearance of bipedalism back by at least a half a million years. Prior to this discovery the oldest primate with bipedal capabilities was believed to be Australopithecus afarensis (~3.9 million years ago).

It is still not clear if Ardipithecus ramidus possessed bipedal capabilities. If so, bipedalism’s first appearance occurs very close to the time that the ape and human lineages supposedly split. This allows the forces of natural selection only a few hundred thousand years to generate bipedalism—a time period far too short, according to evolutionary biologists, given the extensive anatomical changes necessary for a quadrupedalism-to-bipedalism transition.

If A. ramidus lacked bipedal capabilities, this too creates problems for the evolutionary paradigm. Evolutionary biologists view A. ramidus as the ancestral species that gave rise to A. anamensis. In this scenario, bipedalism must have emerged in less than two hundred thousand years—an even shorter (hence less feasible) time period for the enormous species' differentiation to occur.

Paleoecology of Bipedalism

Recent work characterizing the environment in which the oldest bipedal primates lived yielded unexpected results. A. ramidus and A. anamensis did not live in open savannas, but rather in woodlands and forests.15 Moreover, recent studies indicate that A. afarensis lived in a mix of woodland and open savanna environments.16

A newly discovered australopithecine species, Australopithecus bahrelghazali, recovered in Chad and dated to be between 3.0 and 3.5 million years in age also lived in a mixed habitat.17 And the newly discovered hominid specimen, Kenyanthropus platyops, dated at 3.5 million years in age, lived in a predominantly woodland and forest environment that included open grasslands.18

In the words of anthropologist and science writer Roger Lewin, “The popular notion of our forebears striding out of dense forest onto grassland savanna is likely to be more fiction than fact.”19 This new recognition, expressed by Lewin, creates profound trouble for the evolutionary paradigm, eliminating the evolutionary driving force long predicted to have generated bipedalism.

A recent geological study conducted to understand the aridification of East Africa—the event that caused a transformation of its woodlands into an open savanna—provides further evidence that the loss of a woodland environment could not have been the driving force in the emergence of bipedalism. This study indicates that the closure of the Indonesian seaway 3-4 million years ago led to reduced rainfall in East Africa and eventually to the transition from woodlands to grasslands.20 By the time East Africa became arid, bipedalism had already appeared.

Static Bipedalism

A recent mathematical and statistical analysis of over two hundred pelvic bone specimens from apes, extinct hominids, and modern humans uncovered a historical pattern that challenges the evolutionary explanation of bipedalism at its core.21 Instead of gradually changing over time, bipedalism appeared suddenly, remained static (unchanged) for a long period of time, then underwent rapid transformation before again remaining static and undergoing another rapid change.

Australopithecines, the first bipedal primates, possessed a form of bipedalism distinct from that of the Homo primates. Australopithecines displayed facultative (optional) bipedalism whereas the Homo genus possessed and continues to possess obligatory bipedalism. Though australopithecines existed for nearly 3 million years, their bipedalism did not gradually change into the obligatory bipedalism of the Homo primates. Rather, it remained static throughout the duration of the australopithecine’s existence.

With the appearance of the Homo genus, obligatory bipedalism suddenly appeared in the fossil record. From an evolutionary perspective, this quick change demanded a rapid transition process from facultative to obligatory bipedalism. Obligatory bipedalism in the Homo genus has remained static for nearly 2 million years. Interestingly, Homo erectus and Neandertals possessed an identical form of bipedalism, but a form distinct from that seen in modern humans. With the appearance of modern humans, yet another form of bipedalism suddenly appeared and has continued since its introduction.

While the pattern of stasis punctuated by sudden change seen in the fossil record runs counter to evolutionary expectations, it serves as a clear indicator of God’s creative activity. If God created the australopithecines, the Homo bipedal primates, and other similar genera—a prediction can be made that the bipedalism possessed by each genus should be optimal within the context of its respective environment and lifestyle. Once created, natural selection would be expected to keep each type of bipedalism static, since any change would result in a nonoptimal form of bipedalism, compromising fitness.22 Moreover, given the differences in lifestyle and environment, it readily follows from a creation model perspective that God would create the australopithecines and Homo primates with different forms of bipedalism, as observed in the fossil record.

Conclusion

Recent scientific advances in the natural history of bipedalism provide a useful collection of observations that allow evaluation of both evolutionary and biblical scenarios for the origin of humanity. The sudden and early appearance of bipedalism in the fossil records allows insufficient time for bipedalism to emerge through natural process biological evolution. The fossil record also fails to reveal a pattern of gradual transformation from rudimentary bipedalism to a more sophisticated, efficient form. The absence of any significant evolutionary pressure to force these changes makes them even more remarkable.

A sudden and early appearance with two periods of stasis interspersed by rapid change defines bipedalism’s natural history. These characteristics perfectly match the pattern special creation would predict.

A biblical creation model, in which God creates large bipedal primates, predicts long periods of stasis; a perfect Creator could be expected to bring about a form of bipedalism ideally suited for His creatures’ environmental, predatory, and competitive challenges. The recent scientific discoveries provide explicit evidence that one of the most important defining features of humanity—bipedalism—came about through God’s direct creative activity. Though not human, bipedal primates were designed for a specific purpose and function. They were the handiwork of a Creator.

With the evidence of such care toward bipedal primates, the prestige of human beings, uniquely created in the image of God, takes on tremendous significance. Being purposefully created human by a God who cares makes a person’s life worth living. A society that understands such implications can extend value, meaning, and purpose to its people. And that understanding makes the discoveries related to a leap to two feet priceless.

References:

  1. Genesis 1:26-27; Genesis 2:7; Genesis 2:22; Mark 10:6; Matthew 19:4; Psalm 8:4-5.
  2. Hugh Ross, “Can Science Test a ‘God-Created-It’ Model? Yes!” Facts for Faith (Q2 2000), 40-47; 55-58.
  3. John G. Fleagle, “Primate Locomotion and Posture,” in The Cambridge Encyclopedia of Human Evolution, paperback edition, ed. Steve Jones, Robert Martin, and David Pilbeam (New York: Cambridge University Press, 1994), 75-85.
  4. Eric Delson et al., eds., Encyclopedia of Human Evolution and Prehistory, 2d ed. (New York: Garland Publishing, 2000), 394-95; B. Bower, “African Fossils Flesh Out Humanity’s Past,” Science News 155 (1999), 262; Elizabeth Culotta, “A New Human Ancestor?” Science 284 (1999), 572-73; Jean de Heinzelin et al., “Environment and Behavior of 2.5 Million-Year-Old Bouri Hominids,” Science 284 (1999), 625-29; Berhane Asfaw et al., “Australopithecus garhi: A New Species of Early Hominid from Ethiopia,” Science 284 (1999), 629-35.
  5. Roger Lewin, Principles of Human Evolution: A Core Textbook (Malden, MA: Blackwell Science, 1998), 219-22.
  6. Lewin, 227.
  7. Lewin, 224-26.
  8. Fleagle, 75-78.
  9. Lewin, 227.
  10. Lewin, 218; Robert Martin, “Walking on Two Legs,” in The Cambridge Encyclopedia of Human Evolution, paperback edition, ed. Steve Jones, Robert Martin, and David Pilbeam (New York: Cambridge University Press, 1994), 78; Fred Spoor et al., “Implications of Early Hominid Labyrinithine Morphology for Evolution of Human Bipedal Locomotion,” Nature 369 (1994), 645-49.
  11. Tim D. White et al., “Australopithecus ramidus, a New Species of Early Hominid from Aramis, Ethiopia,” Nature 371 (1994), 306-12; Henry Gee, “New Hominid Remains Found in Ethiopia,” Nature 373 (1995), 272.
  12. Tim D. White et al., “Corrigendum,” Nature 375 (1995), 88.
  13. Meave G. Leakey et al., “New Four-Million-Year-Old Hominid Species from Kanapoi and Allie Bay, Kenya,” Nature 376 (1995), 565-71.
  14. Meave G. Leakey et al., “New Specimens and Confirmation of an Early Age for Australopithecus anamensis,” Nature 393 (1998), 62-66; B. Bower, “Early Hominid Rises Again,” Science News 153 (1998), 315.
  15. Meave Leakey and Alan Walker, “Early Hominid Fossils from Africa,” Scientific American (June 1997), 74-79; Clark Spencer Larsen, Robert M. Matter and Daniel L. Gebo, Human Origins: The Fossil Record, 3d ed. (Prospect Heights, IL: Waveland Press, 1998), 46.
  16. Lewin, 258; 266-69.
  17. Michel Brunet et al., “The First Australopithecine 2,500 Kilometers West of the Rift Valley (Chad),” Nature 378 (1995), 273-75.
  18. Meave G. Leakey et al., “New Hominid Genus from Eastern Africa Shows Diverse Middle Pliocene Lineages,” Nature 410 (2001), 433-40.
  19. Lewin, 222.
  20. Mark A. Cane and Peter Molnar, “Closing of the Indonesian Seaway as a Precursor to East Africa Aridification Around 3-4 Million Years Ago,” Nature 411 (2001), 157-62.
  21. François Marchal, “A New Morphometric Analysis of the Hominid Pelvis Bone,” Journal of Human Evolution 38 (2000): 347-65.
  22. Niles Eldredge, Reinventing Darwin: The Great Debate at the High Table of Evolutionary Theory (New York: John Wiley, 1995), 78-81.

Sidebar: The Evolutionary Perspective of Human Origins

Fazale R. Rana

Current models for human evolution describe modern humans as gradually emerging from more primitive “hominids” (members of the primate family Hominidae) through descent with modification via natural selection and mutations. Evolutionary biologists think this process began around 5 million years ago when hominids and apes supposedly diverged from a shared ape-like ancestor.1

Australopithecines occur in the fossil record between 4.5 to 1.5 million years ago as the first bipedal primates.2 The genus Australopithecus encompasses a diverse group of hominids with ape-size brains; ape-like cranial, facial, and dental features; an ape-like torso and upper limbs; and limited bipedal capabilities distinct from modern humans.3

Until recently, paleoanthropologists viewed the australopithecines as part of the evolutionary pathway leading to modern humans. Controversy now centers around the role of australopithecines in human origins with the discovery of a new hominid genus, Kenyanthropus, dated at 3.5 million years in age.4 Some paleoanthropologists suggest that Kenyanthropus gave rise to Homo bipedal primates.5

No consensus view exists among paleoanthropologists to describe the evolutionary relationships among (extinct) australopithecines and a closely related genus, Paranthropus (originally considered “robust australopithecines”).6 However, the latter’s relatively large size and other unique, distinguishing features prompted paleoanthropologists to reclassify the robust australopithecines as a separate genus. Paleoanthropologists view Paranthropus as an evolutionary dead end. Given the bewildering array of species, paleoanthropologists are unclear as to which of the australopithecines could have given rise to the Homo genus of bipedal primates.

Homo bipedal primates first appear in the fossil record about 2 million years ago. Traditionally Homo habilis was regarded as the first Homo bipedal primate and the key transitional species linking the australopithecines to the Homo genus. However, newly recognized features (features more closely aligned with those of the australopithecines than with those of other Homo bipedal primates such as Homo erectus), caused H. habilis to be reclassified as an australopithecine.7 This new understanding seriously weakens the position of H. habilis as a transitional species, thus leaving a discontinuity in the hominid phylogeny.

Homo erectus and Homo neandertalensis are the two bipedal primates that have been most closely linked to modern humans. However, recent work has all but severed the link between modern humans and H. erectus, and has completely cut the connection between Neandertals and modern humans.8 Paleoanthropologists increasingly regard H. erectus as representing a side branch that resulted in an evolutionary dead end, since this bipedal primate was confined to Asia, and analysis of DNA isolated from three distinct Neandertal remains all indicate that Neandertals made no contribution to human genetic makeup.

As with the australopithecines, a menagerie of Homo bipedal primates existed for most of the last 2 million years. Paleoanthropologists, unable to reach a consensus on the evolutionary relationships among the members of the Homo genus, have been unable to identify a direct ancestor to modern humans.9 Nevertheless, many evolutionary biologists are convinced these relationships exist and the missing ancestor of modern humans will someday be discovered.

References:

  1. Richard Morris, The Evolutionists: The Struggle for Darwin’s Soul (New York: W. H. Freeman, 2001), 34-37.
  2. B. A. Wood, “Evolution of Australopithecines,” in The Cambridge Encyclopedia of Human Evolution, paperback edition, ed. Steve Jones, Robert Martin and David Pilbeam (New York: Cambridge University Press, 1994), 231-240.
  3. Roger Lewin, Principles of Human Evolution: A Core Textbook (Malden, MA: Blackwell Science, 1998),  241-282.
  4. Meave G. Leakey et al., “New Hominid Genus from Eastern Africa Shows Diverse Middle Pliocene Lineages,” Nature 410 (2001), 433-40; Daniel E. Lieberman, “Another Face in Our Family Tree,” Nature 410 (2001), 419-20.
  5. B. Bower, “Fossil Skull Diversifies Family Tree,” Science News 159 (2001), 180.
  6. Lewin, 297-307.
  7. Bernard Wood and Mark Collard, “The Human Genus,” Science 284 (1999), 65-71; B. Bower, “Redrawing the Human Line,” Science News 155 (1999), 267.
  8. J. M. Bermudez de Castro et al., “A Hominid from the Lower Pleistocene of Atapuereca, Spain: Possible Ancestors to Neandertals and Modern Humans,” Science 276 (1997), 1392-95; Ann Gibbons, “A New Face for Human Ancestors,” Science 276 (1997), 1331-33; Fuz Rana, “Up (and Away) from the Apes,” Connections 1, no. 2 (2000), 3-4; Hugh Ross, “Neandertal Takes a One-Eighty,” Facts & Faith 11, no. 3 (1997), 4-5; Fazale R. Rana, “DNA Study Cuts Link With The Past,” Connections 2, no. 3 (2000), 3; Fazale R. Rana, “Neanderthal Genetic Diversity: From Missing Link to Special Creation,” Facts for Faith (Q4 2000), 5.
  9. Lewin, 385-428.

Sidebar: Biblical Perspective on the Hominids

Fazale R. Rana

If humans are made in the image of God through His direct creative activity, then what is the proper biblical perspective on hominids or bipedal primates? The biblical model employed here views bipedal primates as separate species that have gone extinct since their creation. The genera Australopithecus, Kenyanthropus, and Paranthropus—all ape-like creatures—possessed limited intelligence, limited bipedal capability and, in some cases, extremely crude tools. The bipedal primates assigned to the Homo genus, such as Homo erectus and Homo neandertalensis walked upright, used crude tools, possessed intelligence and perhaps even emotional capacity, yet they were devoid of spiritual capacity and, therefore, must be regarded as distinct from modern humans.1

Bipedal primates were not created in the image of God. Paleoanthropologists have no indication from the archeological record that Neandertals, or any bipedal primates, engaged in religious activity.2 Although the Homo bipedal primates used tools, they were crude and qualitatively distinct from the sophisticated tools used by modern humans.3 Neandertals, in all likelihood did not possess language capacity.4 Genesis 1 makes no specific allusion to bipedal primates. Their creation by God on Days 5 and 6 in the group of nephesh or animals endowed with will, emotion, and intelligence can be inferred.

References:

  1. Hugh Ross, The Genesis Question (Colorado Springs, CO: NavPress, 1998), 54-55; 110.
  2. Eric Delson et al., eds., Encyclopedia of Human Evolution and Prehistory, 2d ed. (New York: Garland Publishing, 2000), 615-17.
  3. Tom Clarke, “Relics: Early Modern Humans Won Hand Over Fist,” Nature Science Update, (6 February 2001); Steven E. Churchill, “Hand Morphology, Manipulation, and Tool Use in Neandertals and Early Modern Humans of the Near East,” Proceedings of the National Academy of Sciences, USA 98 (2001): 2953-55; Wesley A. Niewoehner, “Behavioral Inferences from the Skhul/Qafzeh Early Modern Human Hand Remains,” Proceedings of the National Academy of Sciences, USA 98 (2001): 2979-84.
  4. Christopher Stringer and Robin McKie, African Exodus: The Origin of Modern Humanity (New York: Heary Holt and Company, 1996), 85-114.

Author's Update

By Fazale R. Rana

During the final publication stages of this article, a team of paleontologists from the University of California, Berkeley reported the discovery of hominid remains dated between 5.2 and 5.8 million years ago and described this animal’s environment.1 The results of their work bolster the case for the supernatural appearance of bipedalism.2

Paleoanthropologists making this discovery assigned the fossil remains to Ardipithecus ramidus. Analysis clearly indicates that A. ramidus walked erect. This dramatic discovery not only pushes the hominid fossil record back by nearly one million years but also places the appearance of bipedalism coincidental to the first appearance of hominids. Bipedalism, indeed, appears suddenly in the fossil record.

The paleoanthropologists also determined that A. ramidus lived exclusively in a wet woodland environment. Likewise, the A. ramidus specimen dated at 4.4 million years in age lived in a wet woodland habitat.3 These discoveries fully eliminate the evolutionary driving force for bipedalism’s emergence. As one researcher commented, these discoveries "challenge some long-cherished ideas about the mode and timing of hominid evolution."4

References:

  1. Yohannes Haile-Selassie, “Late Miocene Hominids from the Middle Awash, Ethiopia,” Nature 412 (2001), 178-81; Giday WoldeGabriel et al., “Geology and Paleontology of the Late Miocene Middle Awash Valley, Afar Rift, Ethiopia,” Nature 412 (2001), 175-78.
  2. Henry Gee, “Return to the Planet of the Apes,” Nature 412 (2001), 131-32; Michael Balter and Ann Gibbons, “Human Evolution: Another Emissary from the Dawn of Humanity,” Science 293 (2001), 187-89.
  3. Giday WoldeGabriel et al., “Ecological and Temporal Placement of Early Pliocene Hominids at Aramis, Ethiopia,” Nature 371 (1994), 330-33.
  4. Balter and Gibbons, 187-88.

Body and Soul Part II: Why the Soul is Immaterial

By J. P. Moreland, Ph.D.

Tom's mother lies in a hospital bed in a darkened room. Suddenly, the blips on her heart monitor become erratic. Within seconds, a flat line appears. A nurse hurries into the room and turns the monitor off. After a long illness, Tom’s mom is dead. But is she?

What if Tom's mother’s soul survives as a distinctly separate entity after her brain waves cease and her human body no longer lives? If such is the case, the stage is set for discussion of life beyond death, and the subject of the immaterial nature of the soul takes on deep significance. Immaterial in this context means "having no physical or material reality," not that Mom's soul is inconsequential. Precisely because such a human being matters so much, understanding the relationship between body and soul carries great importance.

Part I of this series showed how the properties that make up one’s stream of consciousness are not physical, but genuinely mental. This article, Part II, argues that a human being’s soul or self (e.g., a mother’s soul) is immaterial (or non-material). Before considering the arguments, the reader may wish to review briefly the nature of a physical substance.

Substances are particular individual things like acorns, carbon atoms, or moms. A substance, like a particular mom, cannot be in more than one place at the same time (no matter how much she might like for her children to believe otherwise).

Substances are basic fundamental things. They are not in other things or aspects of other things. Though an adult child may be convinced at times that Mom lives inside his head, she is in fact a substance, a separate entity made up of parts, properties, and capacities (dispositions, tendencies, and potentialities). Mom has a number of parts such as eyes, mouth, a broken fingernail, and a stubbed toe. Properties include her weight and age. New properties can change, yet the substance remains the same throughout that change. For instance, Mom's hair may go from the property of gray to the property of blonde, but she'll always be Mom.

In addition, Mom has some capacities or potentialities that are not always actual. For example, she has the capacity to invoke discipline even though she may choose to wait until Dad comes home.

Substance dualists assert that as a human, Mom consists of an immaterial substantial soul with a physical body that is not identical to the soul. Because substance dualists believe that the properties of ego and consciousness are without physical material, they are also property dualists.  However, an individual can be a mere property dualist without being a substance dualist by accepting the immateriality of consciousness but holding the belief that its owner is the body or, more likely, the brain. In contrast with mere property dualism, substance dualists believe that the brain is a physical thing with physical properties and the mind or soul is a mental substance that has mental properties.

When Mom is in pain, her brain has certain physical properties (e.g., electrical, chemical), and the soul or self has certain mental properties (e.g., the conscious awareness of pain). Her soul possesses its experiences. It stands behind, over, and above them and remains the same throughout her life. Mom's soul and brain can interact with each other, but they are different particulars with different properties. Since her soul is not to be identified with any part of the brain or with any particular mental experience, then it may be able to survive the destruction of the body.  Substance dualists accept the existence of both mental properties and substances.

Three main forms of substance dualism are currently being debated. However, a simple argument can be made for that which all three positions hold in common; a human being’s self or ego as an immaterial substance that bears consciousness.1  

A Case for the Immaterial Nature of the Self

Recent literature offers at least four arguments for the disembodied identity of the soul.

1. Basic Awareness of the Self

When an individual such as a mom pays attention to her own consciousness, she becomes aware of her own self (i.e., her ego, "I," her center of consciousness) as being distinct from her body and from any particular mental experience she has. Mom simply has a basic direct awareness of the fact that she is not identical to her body or her mental events; rather, she is the self that has a body and a conscious mental life.

The following example illustrates this point. Mom's son looks at chocolate chip cookies sitting on a counter and walks toward them. In so doing, he experiences a series of what are called phenomenological objects or cookie representations. That is, several different cookie experiences replace one another in rapid succession. As he approaches the cookies, cookie sensations change. The aroma grows stronger.  What originally may have appeared to be ants take shape and become recognized as chocolate chips. Further, because of the lighting in the kitchen, the cookies change color slightly, they may be a little on the dark side. The cookies don’t actually change in smell, shape, or color; but the son's cookie "experiences" do.

Of course, the son is aware of all the different experiences of the cookies during the fifteen seconds it took to walk across the room. But if paying attention, the son is also aware of two more things. First, he does not simply experience a series of sense-images of a cookie. Rather, through self-awareness, the fact is also experienced that it is "I" the self who has each cookie experience. Each cookie sensation produced at each angle of perspective has a perceiver who is I. An “I” accompanies each sense experience to produce a series of awarenesses—“I am experiencing a cookie sense image now".

The son is also aware of the basic fact that the same self that currently has a fairly large cookie experience (especially as the hand comes to within reach of the cookie) is the very same self as the one who had all of the other cookie experiences preceding this current one. In other words, through self-awareness, one gains an awareness of the fact that "I" am an enduring "I" who was and is (and will be) present as the owner of all the experiences in the series.

These two facts—"I" am the owner of self-experience, and "I" am an enduring self who exists as the same possessor of all self-experience through time—show that a person is not identical to his experiences. Self (or “I) is the thing that has them. In short, “I” is a mental substance. Only a single enduring self can relate and unify experiences, a fact that property dualists and physicalists cannot adequately account for or explain away.

2. More than Third Person

A complete physicalist description of the world would be one in which everything would be exhaustively described from a third-person point of view in terms of objects, properties, processes, and their spatiotemporal locations. For example, a description of a cookie in a room would go something like this: “An object exists three feet from the south wall of the kitchen and two feet from its east wall, and that object has the properties of being light brown, circular, sweet, and so on."

The first-person point of view is the vantage point used to describe the world from one's own perspective. Expressions of a first-person point of view use what are called indexicals—words such as “I,” “here,” “now,” “there,” and “then.” Here and now are where and when “I”am. There and then are where and when “I” am not. Indexicals refer to me myself. “I” is the most basic indexical and refers to a self that is known by acquaintance with one's own consciousness in acts of self-awareness. “I” am immediately aware of my own self and “I” know who “I” refers to when “I”use it; it refers to an individual as the self-conscious self-reflexive owner of his own body and mental states.

According to physicalism, no irreducible privileged first-person perspectives exist. Everything can be exhaustively described in an objective language from a third-person perspective. A physicalist description of a mom would say, “There exists a body at a certain location that is five feet tall, weighs 115 pounds,” and so forth. The property dualist would add a description of the properties possessed by that body, such as the body is feeling pain, thinking about lunch, or can remember being on vacation with her children in Grandview, Missouri, in 1965.

But no amount of third-person description can capture Mom's own subjective first-person acquaintance of her own self in acts of self-awareness. In fact, for any third-person description, an open question always exists as to whether the person described in third-person terms is the same person as Mom. She knows her self not because she knows some third-person description of a set of mental and physical properties and because a certain person satisfies that description. She knows herself as an ego immediately through being acquainted with her own self. She expresses that self-awareness by using the term “I.”

 “I”refers to Mom's own substantial soul. It does not refer to any mental property or bundle of mental properties she is having, nor does it refer to any body described from a third-person perspective. “I”is a term that refers to something that exists, and does not refer to any object or set of properties described from a third-person point of view. Rather, “I”refers to Mom's own self with which she is directly acquainted and who, through acts of self-awareness, she knows to be the substantial possessor of her mental states and her body.

3. The Modal Argument

Thought experiments have rightly been central to debates about personal identity.  For example, people are often invited to consider situations in which two persons switch bodies, brains, or personality traits or in which a person exists disembodied.  In these thought experiments, someone argues in the following way: Because a certain state of affairs S (e.g., Mom's existing in a disembodied state) is conceivable, one can justifiably think that S is metaphysically possible.  Now if S is possible, then certain implications follow about what is/is not essential to personal identity (e.g., Mom is not essentially a body).

People use conceiving as a test for possibility/impossibility throughout their lives.  Mom knows that her son can become President (even if she thinks it is highly unlikely) because she can conceive it to be so. She knows square circles are impossible because they are inconceivable, given her knowledge of being square and being circular.  To be sure, judgments that a state of affairs is possible/impossible grounded in conceivability are not infallible.  They can be wrong.  Still, they provide strong evidence