[blam]

"My money is on solar activity, insolation variations."

I will consider all possibilities. We probably had some of all.

[IYAAYAS]

Thanks for all the good leads, got lotsa good reading to do.

Since we're considering all possibilities...I've always been curious about that dark spot on the sun. What if a small planet closer than mercury got sucked in a long time ago. It would have caused solar-system wide changes, like maybe the drying of mars etc.