Earth's cycles have always intertwined somewhat, imho. I believe that greenhouse gases emitted from volcanism during the 'Snowball Earth' periods, (and as you said, in some local
areas) kept things going... kept water fluid in most cases, etc. Yes, the sun was smaller then, but was Earth's core?

"The NeoProterozoic "Snowball Earth" models are in interesting example of non-steady states of the biosphere. Other models of the Archean might need to be similarly inventive, rather than boring steady-state systems."

Not just boring, Nick, not believable. Earth seemed to always have had an 'out' of what seemed to mark it's end. I agree that more study should be done... full agreement on a final analysis, and dates so that school kids could get a much bigger and accurate picture. :) I've read papers that talk about the same epoch and circumstances, but don't necessarily agree on a specific time, i.e., they are off by a few million and sometimes billion years (goes for Mars related papers as well). That has a way of changing things and leads the reader to use his/her own common sense. ;)

I've read papers that say:

1) Mars was internally dead by the time the Hellas impact occured. They are basing that on the lack of evidence of errosion by weathering or even tectonic/plate movement.

2) Others say that volcanism in
Tharsis was alive and well during the time of impact and that Tharsis may have even tried to compensate for the Hellas impact shock. Aside: Hellas is the general area where MOLA found the 'echoes' or leftover traces of the Martian magnetosphere.

As in studying the Earth, maybe they're both right to some extent.

Cheers and Happy Father's Day!

Marcia