On 12/08/2012 5:32 AM, Mike Dworetsky wrote:
Yousuf Khan wrote:
On 09/08/2012 2:42 PM, dlzc wrote:
Was only ~2.2 billion years from the Theia encounter, that wiped out
whatever might have been on Earth before.

The Theia encounter (if it happened), would've happened only a few
hundred million years after formation, maybe let's say 4.5 billion
years ago. Pretty much right at the beginning of the formation, so
almost no difference.

The Late Heavy Bombardment era was around 3.8-4.1 billion years ago,
maybe this is what he meant. The Moon was heavily cratered, and
presumably so was the Earth, resetting the clock for evolution of life.
The LHB does have some criticisms that I won't go into, but the Theia
event almost certainly happened very early on and is the only viable
explanation so far for the existence of Earth's large Moon and the
similarities of lunar and terrestrial isotope signatures, for example.

Well, the Late Heavy Bombardment makes more sense as a late event that
happened after solar system formation. However 3.8-4.1 billion years ago
is still a far cry from 2.2 billion years ago. So I wonder what event
might have happened 2.2 bya, that he might have been thinking of?

Yousuf Khan