"Perhaps the primary reason for drawing attention to this is because of its
relevance to abiogenesis, the earth's early atmosphere and to the timescale
available. Zhang refers to 4.45 Ga as the probable time of 'the last
Martian-size giant impact that stripped Earth's protoatmosphere and
rehomogenised Earth.' Thereafter, in Zhang's view, the Earth can be treated
as a closed system - despite subsequent bolide impacts. Models of
abiogenesis need to start at this point (100 Ma - 150 Ma later than has been
widely thought). (Having drawn attention to reducing time availability in
the Archaean, I thought it relevant also to point out this reduction in time
availability)."
The time interval between 4.45 GYA and 3.80 GYA is still 650 MY, which is
the entire time since the hayday of the Ediacaran fauna. I have to say that
still seems like plenty of time to me.
I know you don't agree with this assessment, but so far your only reasons
have amounted to vague assertions about the difficulty of abiogenetic
processes and the violence of bolide impacts. What I would like to know is
if you have any specific, concrete reasons for questioning the adequacy of
this amount of time? I mean, let's take a page from Neal Roys posts: can
you propose any testable causal mechanisms that would demonstrate that even
this length of time is inadequate?
Kevin L. O'Brien