Leonard David's INSIDE OUTER SPACE

An artistic conception of the early Earth, showing a surface pummeled by large impacts, resulting in extrusion of deep-seated magma onto the surface. At the same time, distal portion of the surface could have retained liquid water.
Artwork by Simone Marchi

New research suggests that asteroidal collisions not only severely altered the geology of the “Hadean Earth” (meaning hell-like), but likely played a major role in the subsequent evolution of life on Earth as well.

That Hadean period is pegged at roughly 4.0 to 4.5 billion years ago.

In the very beginning of Earth’s formation, the first 500 million years, that Hadean epoch is a less well-known period. It was assumed that it was wildly hot and volcanic and everything was covered with magma – completely unlike the present day.

Large collisions as late as about four billion years ago may have repeatedly boiled away existing oceans into steamy atmospheres.

How big and how frequent were those incoming bombardments, and what were their effects on the surface of the Earth?

According to Elkins-Tanton, director of the School of Earth and Space Exploration at Arizona State University (ASU), the new research is attempting to bridge that time from the last giant accretionary impact that largely completed the Earth and produced our moon, to today’s current state of affairs – plate tectonics and a habitable surface.

Rate of impactors

Researchers found that on average, Hadean Earth could have been hit by one to four impactors that were more than 600 miles wide and capable of global sterilization, and by three to seven impactors more than 300 miles wide and capable of global ocean vaporization.

“Prior to approximately four billion years ago, no large region of Earth’s surface could have survived untouched by impacts and their effects,” says Simone Marchi of NASA’s Solar System Exploration Research Virtual Institute at the Southwest Research Institute. “The new picture of the Hadean Earth emerging from this work has important implications for its habitability,” the scientist noted in an ASU press statement.

“During this time, the lag between major collisions was long enough to allow intervals of more clement conditions, at least on a local scale,” says Marchi. “Any life emerging during the Hadean eon was likely resistant to high temperatures, and could have survived such a violent period in Earth’s history by thriving in niches deep underground or in the ocean’s crust.”

An international team of scientists published their findings in the July 31, 2014 issue of Nature.

Go to:

http://www.nature.com/nature/journal/v511/n7511/full/nature13539.html

NOTE: While there, give a listen to a related audio presentation by Simone Marchi that discusses the new bombardment model of the early Earth. It’s located on the right side of the web page.