Fossilized Horses' Teeth Provide Evidence Of Biggest Climate Shift Between KT & Present - Reuters

[hatrack]

EDIT

Paleontologists have known for more than a century that many species went extinct at the transition between the Eocene and Oligocene, based on the fossil record before and after the shift. However, they lacked the analytic tools to determine how much temperature change there was over how long a period, and exactly when it occurred.

Fossil research showed that creatures that might be at home in the tropics, like warm-loving crocodilians, roamed what is now Nebraska on the American Great Plains before the temperature transition. After the transition, they were gone. Scientists believe changes in ocean currents were to blame for the shift.

To figure out the details of what French researchers dubbed Grande Coupure -- "big cut" -- MacFadden and his co-authors examined the preserved teeth and bones of fossil horses and another cloven-hoofed mammal called an oreodont.

They analyzed oxygen and carbon isotopes contained in the samples; oxygen isotopes told the scientists at what temperature the teeth were formed and carbon isotopes revealed the relative humidity, the University of Florida said in a statement. Using isotope data and precise locations and dates for the fossil teeth, the researchers were able to pinpoint the details of the transition, the biggest climate change since the end of the dinosaurs about 65 million years ago.

EDIT

http://www.planetark.org/dailynewsstory.cfm/newsid/40243/story.htm

[idealistMO]

1. climate change.....

I wonder what caused that climate change back then?? Solar cycles?

[tabatha]

2. The composition of Earth's atmosphere

has not always been constant - so the reasons for climate change have been different.

This oxygen-nitrogen atmosphere is the "third atmosphere". 200 - 250 million years ago, up to 35 percent of the atmosphere was oxygen (bubbles of ancient atmosphere were found in an amber).

link:
http://en.wikipedia.org/wiki/Earth's_atmosphere

http://tinyurl.com/4k75h

if the first one does not work.

[hatrack]

3. Probably the closing of the Isthmus of Panama

MAJOR scrambling of ocean currents, with ensuing havoc. At least, that's the generally accepted geological and paleoclimate picture of what happened.