Where Science and Faith Converge

Late Heavy Bombardment: Not So Sterile

By Jeff Zweerink - June 24, 2009

Fireworks, thunderbirds, thunderstorms, NASCAR races, earthquakes–each of these phenomena displays power, generally accompanied by loud noises. But they all pale in comparison to the fireworks that occurred early in Earth's history. After a Mars-sized object collided with Earth and formed the Moon (4.5 billion years ago) a predictable rain of asteroids and comets bombarded Earth's surface. Though the "rain" generally decreased, it dramatically intensified between 4.1 and 3.9 billion years ago. Scientists refer to this period of increased collisions as the Late Heavy Bombardment (LHB). And new research suggests that, despite the onslaught, an existing life may have survived.

With numerous impactors greater than 30 miles in diameter (and the number of impactors grows as the size decreases), events during the LHB affected Earth's surface significantly. Most astronomers and earth scientists had originally thought that each of these large events completely sterilized the Earth and turned its surface into a sea of magma. Nevertheless, shortly (geologically speaking) after the end of the LHB, an abundance of single-celled life appears to have populated the Earth. The evidence for abundant life so early after this catastrophic period in Earth's history supports key predictions of RTB's creation model. Based on biblical data, the model predicts that life arose (1) suddenly, (2) early in the planet's history, and (3) in hostile conditions.

New research by two geophysicists provides a more detailed picture of the LHB's impact on Earth and its life. The two scientists developed a computer simulation that modeled the distribution of impactor sizes and frequency as they hit Earth as well as how the energy from each impact propagated through the crust. In total, the amount of material hitting the planet was 0.01% of Earth's mass. This included nearly 100 impactors that formed craters over 600 miles in diameter.

The model defined a geophysical habitable zone (place where life could exist) on Earth's surface that extended 2.5 miles underground. The pair took into account that scientists have found a number of hyperthermophilic organisms that live in environments where the temperatures reach beyond the boiling point of water (212° F). Thus, as the simulations tracked the energy dissipation from the impact events, any region that exceeded 230° F was deemed sterilized.

The simulations confirmed that each of these large impact events would have sterilized the immediate surface of Earth. However, the simulations typically revealed only 25% sterilization of the habitable zone. In fact, no reasonable distribution of impactors could completely eliminate life from Earth!

These results affect RTB's creation model. Fuz will discuss the details tomorrow. I want to highlight two other points.

First, these findings demonstrated what seems to be a prevailing cycle of hostility-toward-life followed by sustainability. Earth started out uninhabitable and totally unfriendly to life. In order to support human life, the planet underwent a number of substantial changes, such as continental growth (both to provide habitats and regulate temperature) and development of a permanent oxygen atmosphere. Typically, these transformations occur on a geologically short timescale, cause great disruption to Earth's surface, and result in a marked increase in Earth's capacity to support life shortly afterwards. For example, two oxidation events resulted in such a dramatic cooling that glaciers nearly covered Earth's surface. For the most recent of these "snowball Earth events," a dramatic increase in the complexity of life occurred after the glaciers retreated. The names of these periods, the Avalon Explosion and the Cambrian Explosion, implicitly acknowledge their remarkable nature.

Second, the prospect of finding any pristine geological material dating before 3.9 billion years ago seemed hopeless. Although that evidence may still be difficult to find, this research indicates that the LHB didn't wipe out all signs of this hostile period in Earth's history.

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