Dear Yousuf Khan:

On Tuesday, August 14, 2012 9:59:18 PM UTC-7, Yousuf Khan wrote:
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?

I mostly wasn't. Mike was giving me too much credit. At 2.2 Gy, the month was 16 days long. So the Moon had receded from "ten hours" period to 16 days in 2 Gy.

Imagine the tides... even the loft of the Earth's crust...

David A. Smith