Reasons to Believe

Insight into the Late Heavy Bombardment and RTB's Creation Model

I've known people who have had a tumultuous childhood that has left them with emotional scars. The trauma of the first years of Earth's existence resulted in some scarring as well. And, based on a new study, perhaps RTB's origin-of-life model might suffer a scar or two.

Shortly after Earth's formation, an object about the size of Mars crashed into it. The debris from the impact event eventually coalesced to form the Moon. Following that event, asteroids and comets continued to pummel Earth. Some planetary scientists now think that the size and frequency of the impactors diminished rapidly, thereby possibly allowing a crust and oceans to form on the primordial planet between 4.4 and 4.2 billion years ago (bya). But this window of calm was interrupted about 3.9 bya. Early Earth experienced another cataclysm: a geologically rapid succession of impact events that lasted between 20 and 200 million years in duration. Known as the Late Heavy Bombardment (LHB), this event dramatically shaped Earth's–and life's–history.

Two researchers recently conducted computer simulation studies on the effect that the LHB had on Earth and the origin and early history of life. The insights gleaned from this work have profound implications for chemical evolutionary models and for RTB's creation model.

RTB's Origin-of-Life Model

Origins of Life, coauthored by Hugh Ross and me, lays out our origin-of-life model in detail. (See here for an abstract of our model.) We maintain that the God of the Bible is directly responsible for the origin of life. We also understand verse 2 to be the place in the Genesis 1 creation account that refers to the origin-of-life event.

Based on these starting points, our model makes the following scientific predictions:

  1. Life appeared early in Earth's history.
  2. Life appeared under harsh conditions.
  3. Life miraculously persisted under harsh conditions.
  4. Life arose quickly.
  5. First life on Earth was complex.
  6. Life in its minimal form is complex.

Evaluating RTB's Origin-of-Life Model

Scientific evidence provides solid support for these predictions. Geochemical evidence from rock formations that date about 3.8 billion years in age and geochemical and fossil evidence from geological systems that date between 3.2 and 3.5+ billion years in age strongly suggest that life was present on the planet very early in its history. (For descriptions of the studies that reveal this evidence, see Origins of Life and this online article.) Evidence also indicates that life arose in the midst of a hostile milieu, caused by the rain of asteroids and comets pelting the primordial planet.

Even though it consisted of single-cell microbes like bacteria and archaea, first life seems to have been biochemically complex. Work in genomics indicates that minimal life is also quite complex as well. (Please see the books Origins of Life and The Cell's Design and this article for further discussions on this topic).

Traditionally, scientists have believed that life couldn't have appeared on Earth prior to 3.9 bya. They assumed that the planet would've been largely molten due to impacts between 4.5 and 3.8 bya. But recent work on ancient zircons suggests that this time frame wasn't as continuously violent as traditionally thought. The chemical composition of the zircons, which date between 4.2 and 4.4 bya, indicates the occasional presence of liquid water oceans. These more benign conditions would've been more reasonably conducive for chemical evolution and the emergence of life by naturalistic means.

Still, the conditions of early Earth–because of the LHB–seemed to be largely irrelevant for the origin of life. The prevailing view was this event sterilized the surface and subsurface of the planet, frustrating the origin-of-life process and destroying any life on the planet that may have arisen prior to 3.9 bya. As soon as the Earth recovered from the effects of the LHB, biochemically complex microbial life seemed to emerge suddenly.

The geologically instantaneous appearance of complex life not only fit the predictions made by RTB's origin-of-life model, but also it raised troubling questions for the evolutionary paradigm. It's hard to envision how life could have originated so rapidly and achieved biochemical complexity without the involvement of a Creator.

New Insight into the LHB

As astrophysicist Jeff Zweerink described yesterday, new computer simulation studies indicate that the LHB was not a total sterilization event, nor did it necessarily frustrate the origin of life. Though the simulation shows that the LHB would've indeed completely wiped out surface life, it also shows that some microbes residing in the near subsurface and deep subsurface may have survived. In fact, the LHB actually expanded the habitable zone for hyperthermophiles and thermophiles by creating hydrothermal vent environments. This would've allowed these heat-loving microbes to thrive on the planet at the expense of mesophiles.

The possibility that oceans intermittently existed on the planet as far back as 4.4 to 4.2 bya means that life could've arisen on the planet during that time and survived through the LHB. The simulation team thinks that the LHB created a bottleneck. The mesophiles were eliminated, but the thermophiles and hyperthermophiles endured. After the LHB, life recovered rapidly with the heat-loving survivors and served as the root organisms for the evolutionary tree.

According to the researchers, even if life hadn't emerged prior to the LHB, the hydrothermal environments it generated may have stimulated life's emergence. Many origin-of-life scientists think that life began at hydrothermal vents. The wide-scale generation of such environments would help provide the necessary conditions for high-temperature origin-of-life scenarios.

This new understanding of the LHB not only has important ramifications for evolutionary explanations, it impacts the RTB origin-of-life model as well.

The Impact of the LHB

Based on the results of the computer simulations, it's hard to demonstrate that life originated suddenly on Earth. It's also difficult to assert that the first life on Earth was biochemically complex. In fact, given the possibility that first life could've emerged between 4.4 and 4.2 bya, it's not possible to comment at all on its timing or nature. All we know is that at 3.8 bya a fairly ecologically diverse collection of microbes existed on the planet.

As a consequence, a critical prediction of the RTB origin-of-life model remains unsatisfied, but not necessarily refuted, by the evidence. It's still possible that life did emerge suddenly and in a complex form. There is no scientific data from the geological record at this point to make a determination one way or the other.

At this juncture a key challenge to the evolutionary paradigm seems to have been mitigated. Based on the fact that there is evidence for life on the planet at 3.8 bya and that oceans likely existed on the planet between 4.4 and 4.2 bya, the origin of life conceivably had between 400 and 600 million years to take place.

In the face of these two concessions, it is important to keep in mind how well Genesis 1:2 comports with the scientific evidence. As implied by Scripture, life appears early, under hostile conditions on a water-world planet. Researchers have discovered diamond and graphite inclusions in zircons that date between 4.4 and 4.2 billion years in age that indicate they may have been produced by microbial life.

It is also important to keep in mind that work in genomics indicates that for life to exist independently in the environment it requires approximately 2,000 genes. And to exist as a minimal form, life needs about 400 genes. This intrinsic molecular complexity suggests that when life emerged on Earth, it had to appear in a biochemically complex form, which still satisfies our model's prediction that life in its minimal form is complex.

Also, some researchers, like Stanley Miller, have argued that life would've had to originate in under 10 million years because that's how long it takes for all ocean water to cycle through hydrothermal vents. The temperature and pressures of this environment are so extreme that vital molecules quickly break apart. (Half-lives for these reactions are seconds to minutes in most cases.) In other words, it still appears as if life had to originate rapidly even if it emerged prior to the LHB. However, there is no direct (and RTB model-validating) geological evidence for the sudden appearance of complex life on Earth.

Despite this lack, it doesn't mean that evolutionary explanations escape significant, fundamental difficulties. From a chemical standpoint, the major stages in the naturalistic scenarios are riddled with intractable problems.1 Laboratory experiments designed to recapitulate stages in the origin-of-life process lack geochemical relevance because the experimental conditions are unrealistic when compared to early Earth. Another point worth noting: the simulation team speculated that the LHB could've stimulated life at hydrothermal vents. Again, this scenario is riddled with handicaps.2

It appears that the LHB dramatically impacted the natural histories of Earth and life. And the new insight into this event has left a few scars on RTB's origin-of-life model. While our model requires an adjustment, the simulation study doesn't eliminate agreement between our predictions and the scientific evidence. It also doesn't mean that there is a lack of evidence for life stemming from a Creator's work, or that significant challenges no longer exist for evolutionary models. It simply means that the story for life's origin and early history has become more complex and more interesting than we could've imagined.

Subjects: First Life on Earth

Dr. Fazale Rana

In 1999, I left my position in R&D at a Fortune 500 company to join Reasons to Believe because I felt the most important thing I could do as a scientist is to communicate to skeptics and believers alike the powerful scientific evidence—evidence that is being uncovered day after day—for God’s existence and the reliability of Scripture. Read more about Dr. Fazale Rana

1. See these articles for examples of the problems faced by evolutionary explanations for life's origin: article 1article 2article 3article 4article 5article 6article 7article 8article 9article 10, and article 11.

2. The deficiencies with high-temperature origin-of-life models are canvassed in detail in Origins of Life. Also, see these articles for a more compact description of the problems: herehere and here.