From Newsgroup: talk.origins

https://www.science.org/content/article/ancient-ice-core-could-help-explain-mysterious-shift-earth-s-ice-ages

This is a poorly written news article on a talk given at some geological meeting where some researchers gave their analysis of ice cores dating
to more than 800,000 years ago.

Before a million years ago the ice age cold intervals were around 40,000 years, but something changed around 800,000 years ago and the cold
intervals extended to 100,000 years. The intervals became longer and
the temperature extremes became greater. My take is this is a major
reason for the extinction of ice age fauna. The mega fauna evolved and adapted to the shorter milder intervals, but the longer harsher cold
intervals made them adapt to the glacial periods and they likely lost
the genetic variation that helped them get through the glacial periods.
The mega fauna populations would crash during the warm periods, and then
the populations would expand during the cold interval. The DNA that we
are getting from the last cold interval indicates that there was a
severe population crash during the last warm period when more ice melted
than has yet melted during this warm period. I think that we just
exceeded the max temp of the last warm period and we are still getting
warmer. The populations did recover, but the genetics did not. In
previous cold intervals the genetic diversity recovered (probably more
inbred small populations survived and could mix when their habitat
improved, but this last time the genetic diversity remained low even
though the populations increased to their usual glacial peak population numbers. My take is that only a few inbred populations survived the
last warm period, so even though the population numbers recovered they
lost the genetic variation that they needed to help them adapt to the
next warm period.

My take is that the shift to longer cold periods doomed the mega fauna.
They had longer to adapt to the cold, and slowly lost the genetic
variation that they needed to deal with warmer temperatures. The last mammoths in North America likely died out as small inbred populations
that could not get out of their small alpine valleys.

As noted the article is poorly written. They claim that the warm period
just before the first 100,000 year interval, the CO2 levels spiked by 50
parts per million (ppm). They do not give the level that it spiked
from, and only claim that during that first 100,000 year cold interval
that the CO2 levels hit their lowest recorded level (lower than usual)
at 170 ppm. The article notes that the current CO2 level is above 420
ppm. My guess is that the CO2 level was 50 ppm higher than the average
high for CO2 during previous warm periods, but they do not say what that
level was so that we can compare it to today. They think that something
in the environment changed to increase the CO2 levels and it resulted in
a longer cold interval.

My take is that this change doomed the mega fauna. They became too well adapted to the cold when their populations were at their highest levels.

Ron Okimoto

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