[X] My Assistant

[alan]

At least three massive asteroids smashed into the Earth more than 3.2 billion years ago, and caused such destruction, they dramatically changed the structure and composition of the Earth's surface. This is according to new research from scientists at the Australian National University. The team uncovered evidence of major earthquakes, faulting, and volcanic eruptions that were so violent they dramatically changed the way the Earth's surface was forming. This happened during a period that the Moon also suffered heavy bombardment.

“Our findings are further evidence that the seismic aftershocks of these massive impacts resulted in the abrupt termination of an over 300 million years-long evolutionary stage dominated by basaltic volcanic activity and protracted accretion of granitic plutons,” Dr Glikson said.

“The precise coincidence of the faulting and igneous activity with the impact deposits, coupled with the sharp break between basaltic crust and continental formations, throws a new light on the role of asteroid impacts in terrestrial evolution,” Dr Glikson said.

http://www.universetoday.com/am/publish/ea...ids.html?582005

Could one of the geologist interpret this please.

[Guest_Richard Trigaux_*]

Fascinating prospect!

Why not? With more and more accurate geological data all around the world, we may find more and more unexpected things, such as super large meteorite impacts. But remember the debate about the 64 mllion years transition: at first it was supposed volcanic, but more and more evidences accumulated for an impact. But there are still some points unexplained, and thus still scientists who think about a volcanic origin. So what about 3 billion years?

Remember that there was not one large impact on the Moon, but several, and as far as we know they were not simultaneous. If others are found on Earth, that makes an unusual shower of large bodies with about the same orbit than Earth (The 3 billion years episode seems not to have taken place on other planets).
An explanation was proposed some years ago, I do not remember by who, as what there was an other Earth's satellite which formed at the same time than Earth and Moon. But its orbit was unstable, and it broke in several parts, explaining the shower of large bodies on the Moon (and Earth).

If a body as large as Vesta hit the Earth, I think that all the surface would melt, making life disappear, and even all fossil-bearing layers too. So what happened at that time was not so tremendous, as, as far as we know, life already existed before.

But 3 billion years is a kind of limit: we do not know much older rocks, and thus much older traces of life. So the first billion and a half of the geological evolution of Earth crust and Earth life are still largely unknown. The reason why older rocks are hard to find is that continents were smaller at that time (continents formed progressivelly by accretion of granitic rocks, a process which is still going on). But perhaps most of these ancient rocks still exist deeply buried under the continents.