More on mass extinctions

So I was just reading an article Jason posted in his post entitled Christmas Eve 2050, and it mentions the fact that, aside from the asteroid at the end of the age of dinosaurs, the other great mass extinctions have very mysterious origins.

Now, Michael Cremo's studies of anomalous human evolution data suggest that humans may have been here for possibly billions of years, or at least millions more than the standard anthropological account suggests. What if he's right, and what if humans, then as now, have been civilization-building and causing extinctions on such a wide scale? I could be wrong, but after a million or so years, isn't even the remotest evidence of human civilization, radioactive waste, gone? Surely 62 million years is enough time for human civilization to rise and fall, and disappear without a trace, leaving roaming bands of hundreds of humans alive somewhere on the planet, no? If we do cause a great mass extinction, and nearly wipe ourselves out, and cause this civilization to disappear without a trace, could we start over and, after millions of years, cause another one? Could we have done so already? If the evidence for it disappears, how do we know it hasn't already happened?

Maybe humans really are preordained to do bad, and fall out of ecological balance, but with really really long periods of equilibrium. Maybe that's not so bad, except for times like now.

Hah- crazy.