http://www.psrd.hawaii.edu/Jan01/lunarCataclysm.html
There are several other pieces to this puzzle.
One of them, that the earliest evidence for life
on Earth is 3.8 billion years old, we will come
back to later in the course.
http://www.psrd.hawaii.edu/Jan01/lunarCataclysm.html
There are several issues here that
we care about:
impact frustration,
meteorites bearing amino acids, and
cometary influx of water.