New Research Indicates Early Earth Conditions Were Too Harsh for Life’s Origin
Since the onset of the Industrial Revolution, acid rain has been an environmental problem. Industrial processes introduce sulfur and nitrogen oxides into the atmosphere. These gases react with water to form sulfuric and nitric acids, respectively.
Acid rain causes damage by chemically altering soils and surface waters-harming aquatic life and vegetation. It even corrodes historical monuments and buildings.
According to new research, it appears that acid rain was also a problem quite early in Earth’s history.* Geologists think that this acid rain accelerated the weathering of the early Earth’s crust and would have likely frustrated evolutionary processes needed for the origin of life.
Some background information helps give context to this discovery.
Early Earth Conditions: The Standard View
Generally speaking, geologists have believed that shortly after the earth formed, it existed primarily in a molten state. Most would maintain that neither a permanent crust nor permanent oceans existed on the planet. In these conditions, large amounts of heat would have been liberated from the decay of high levels of radioactive isotopes present on early Earth, rendering the surface a magma ocean. Impact events would have also melted rock on the surface and sub-surface of the planet, vaporizing bodies of liquid water.
Presumably, these conditions persisted from the time of Earth’s formation (about 4.6 billion years ago) until about 3.8 billion years ago. This part of Earth’s history is referred to as the Hadean Era, after Hades, the Greek word for hell.
The Late Heavy Bombardment
Near the end of the Hadean Era, an event known as the Late Heavy Bombardment took place. Asteroids (and maybe comets) pummeled the solar system’s inner planets and moons. Estimates indicate the Earth experienced over 20,000 impact events, with significant environmental damage occurring every 100 years or so.
Once the Late Heavy Bombardment came to an end, the earth developed a permanent crust and liquid water oceans became enduring features.
Early Earth and the Origin of Life
Because of the hellish conditions that existed on the planet, most origin-of-life researchers can’t envision how life could arise, let alone persist, during the Hadean Era or the Late Heavy Bombardment. This conviction raises some troubling questions, since life suddenly appears on Earth at about 3.8 billion years ago, “coincidentally” at the tail end of the Late Heavy Bombardment. (See the book Hugh Ross and I coauthored, Origins of Life for a detailed discussion of the evidence that demonstrates a sudden and early appearance of life on Earth.)
Early Earth Conditions: A New Paradigm?
The standard view of early Earth is being challenged by pieces of zircon recovered from rock formations in western Australia. These minerals date to about 4.2 to 4.4 billion years in age, making them the oldest materials on Earth! Zircon is an extremely hard material with a high melting point and could readily survive the tumult of the Late Heavy Bombardment. These ancient minerals provide an unprecedented opportunity to peer into the time before the Late Heavy Bombardment.
Analysis of isotopes present within the zircons suggests that water oceans and a crust may have existed on Earth, during the Hadean Era, prior to the Late Heavy Bombardment. Other studies support this conclusion. (Go here for a recent example.)
The discovery of more benign conditions on early Earth leaves open the possibility that life may have originated gradually over the course of several hundred million years, instead of immediately after the Late Heavy Bombardment. (Even if life did originate prior to 3.8 billion years ago, it’s difficult to envision how it could have survived the Late Heavy Bombardment.)
New insight into the conditions of early Earth, gleaned from the zircon crystals, turns out to be corrosive to these naturalistic hopes.
Acid Rain on Early Earth
Analysis of lithium isotopes in the ancient zircons indicates that the crust of the early earth experienced extensive weathering most likely from acid rain.
These harsh conditions would have frustrated the origin-of-life process. Even though microbes, called acidophiles, can live under highly acidic conditions, it’s unlikely that they could have originated under those conditions. Acidic conditions inhibit key prebiotic reactions like the Strecker synthesis, the formose reaction, and hydrogen cyanide polymerization. Acidic conditions also promote the breakdown of key biomolecules like proteins and DNA.
The revised insights into the Hadean Era are radically changing our understanding of Earth’s infancy. At the same time this evidence is doing little to facilitate evolutionary explanations for the origin of life. Hopes for a naturalistic explanation for life’s beginnings are slowly dissolving like an icon exposed to the steady pelt of acid rain.
*This study made science news headlines when first published. I discussed the scientific and biblical implications of this research on the June 24, 2008 edition of our podcast, RTB’s Science News Flash. This podcast offers a unique Christian perspective on headline-grabbing discoveries. A free subscription is available through iTunes.