A and periodic extinctions?

Here is one that I am pulling over from on of the astro groups. Might make for some interesting angles if you happen to be thinking about such things as strangely periodic extinction events that dont quite match up with iridium concentration concentration peaks.

Whadja think guys? Could something like this 'line up' with some more of the major 'species yardsales'?

Regards bk

- - - - - - - - - - - - - - - - - - - - - - University of California-Santa Cruz

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April 12, 2001

ANCIENT CLIMATE EXCURSION LINKED TO A RARE ANOMALY IN EARTH'S ORBIT

SANTA CRUZ, CA

Hm, interesting. I know Shackleton and Zachos by reputation, and they're both very good scientists. Without having read the article, I can say that there's very good reason to believe that if they see timing, there's something to see there.

As for the periodicity itself, it's well-known that variations in the Earth's insolation in roughly 28,000, 43,000, and 100,000 intervals (IIRC) that people believe are correlated to variations in the Earth's orbit around the sun. And, at times when these periodicities overlap, we have more severe ice ages. Milankovich frequencies are seen in various natural records (such as ice layers and delta-18-O) certainly throughout the Cenozoic, if not back further.

These frequencies, however, don't drive mass extinctions. At least not directly. The amount of solar radiation the Earth receives influences climates here on Earth. Changes in climates, of course, alter species ranges and weather patterns. However, it takes special conditions to develop ice ages like we have here in the Quaternary

Actually, I have a question for you. Would you be able to tell me how the Milankovich cycles are actually measured - ie. the time spanned in one cycle. I think this must have been worked out by the astro people. They're not pinned back on sedimentary layering and geological dating methods are they because the actual length of a year may change when the earth's orbit becomes more or less elliptical. Do you know if it does?

I was playing around one time with making a timeline - ice ages, meteor impacts (large,) extinctions, ages - and it came out - large meteor impact, ice age, die out, new age.- 'course my information was coming out of the encyclopedia. And a thought - in the orbital area, we are currently circular and at nearest approach to sun, on tilt we are about midway. Bear this in mind while answering Greenhouse hysteria

Are you suggesting the recent (~150 year) rise of CO2 in the atmosphere has something to do with the Earth's approach in orbit to the Sun and