Earth Experienced A Long Period Of Bombardment After Moon’s Formation

Posted: Dec 10 2017, 2:19pm CST | by , Updated: Dec 10 2017, 2:23pm CST, in News | Latest Science News

 
Earth Experienced a Long Period of Bombardment After Moon’s Formation
Artistic rendering of a large collision on the early Earth. Credit: SwRI/Marchi.

Collisions with moon-like objects also brought elements such as gold, silver and platinum to Earth

Earth may have gone through a period of intense bombardment shortly after moon’s creation.

New simulations suggest that Earth in its early evolution collided with moon-sized objects multiple times. The phase was followed by so-called "late accretion," when large impacts delivered materials to young Earth and substantially contributed to its overall mass.

By using simulations, scientists theorize that moon-sized objects delivered more mass to the Earth than previously thought.

"We modeled the massive collisions and how metals and silicates were integrated into Earth during this 'late accretion stage,' which lasted for hundreds of millions of years after the Moon formed," said lead study author SwRI's Dr. Simone Marchi. “Based on our simulations, the late accretion mass delivered to Earth may be significantly greater than previously thought, with important consequences for the earliest evolution of our planet."

Scientists have already known that Earth is shaped by violent processes. The moon was also formed by a violent collision between the early Earth and a small planetary object called Theia.

Previously, researchers estimated that almost half of the Earth’s present mass was delivered during the final stage of terrestrial planet formation. The relative abundance of elements like gold, platinum and iridium in Earth’s mantle points to late accretion, after the end of core’s formation. Prior studies also suggest that all highly siderophile elements delivered by the later impacts were retained in the mantle.

However, new high-resolution impact simulations by researchers at SwRI and the University of Maryland show that substantial portions of the material might have been carried all the way into the Earth's core. The material was either mixed up or thrown back to space and escaped the planet entirely. In any case, the amount of elements added to Earth's mantle reduced, which implies that two to five times more material may have been delivered than previously thought.

“These simulations also may help explain the presence of isotopic anomalies in ancient terrestrial rock samples such as komatiite, a volcanic rock," said SwRI co-author Dr. Robin Canup. "These anomalies were problematic for lunar origin models that imply a well-mixed mantle following the giant impact. We propose that at least some of these rocks may have been produced long after the Moon-forming impact, during late accretion."

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