Fossil Leaves Depict Warm, High Sierra Nevada Mountains in Ancient Past

January 6, 2010
Geologists used fossil leaves to reconstruct the ancient climate of the Sierra Nevada mountain range in California. (Photo: Michael Hren)

( -- A team led by Yale University geologists has reconstructed the climate and elevation of California’s northern Sierra Nevada mountains using organic materials derived from ancient leaves and bacteria.

Their findings, published in the January issue of the journal Geology, show that the Sierra Nevada was warmer in the past and was a prominent topographic feature at least 50 million years ago, helping to resolve long-standing questions regarding the tectonic history of the mountain range.

Until now, many scientists believed the prominence of the developed more recently, with rapid “uplift” over the past 20 million years. In this new study, the team has shown the mountain range was in fact just as tall as far back as 50 million years ago as it is today. They also discovered the region was 6-8 degrees Celsius warmer than today, consistent with other evidence for a globally warmer, ice-free Earth at that time.

The researchers analyzed the composition of waxes from ancient leaves preserved in river sediments from the early Eocene epoch, which in turn informed them of the isotope composition of the precipitation. Because the isotope composition of rain changes as clouds pass over a mountain range and drop precipitation, the team could then infer the height of the mountains at that time. They also used temperature-sensitive bacterial compounds in soils to determine how surface temperatures changed with elevation.

“Because Earth’s has changed over geologic time, it can be difficult to distinguish between local temperature change related to the formation of mountains and past climate,” said first author Michael Hren, who conducted the research while a postdoctoral fellow at Yale and is now at the University of Michigan. “By bringing together two independent records of the ancient environment, we’re able to provide new interpretations of the height of the ancient mountains and how different the regional climate was from today during this time of extreme warming.”

Fifty million years ago, atmospheric carbon dioxide (CO2) levels were more than four times as high as today, so uncovering this past climate has important implications for understanding today’s rising CO2 levels.

“We need to go back to periods of high CO2 and high temperature and try to understand climate on a broad scale,” Hren said. “We have a number of models capable of predicting future climate change, but if we really want to test some of these it’s useful to go back to the ancient environment and see what it looked like during these extreme periods.”

Other authors of the paper include Mark Pagani and Mark Brandon (Yale University) and Diane Erwin (Berkeley Museum of Paleontology).

Explore further: Study: Mountains reached current elevation earlier than thought

More information: DOI:10.1130/G30215.1

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2.1 / 5 (7) Jan 06, 2010
What a delight! Somebody doing work in Paleoclimatology who isn't a hysterical fraud! :-)
1 / 5 (5) Jan 06, 2010
What a delight! Somebody doing work in Paleoclimatology who isn't a hysterical fraud! :-)

Very much agreed. Surprisingly this article is completely devoid of alarm or exageration. A great step in the right direction regardless of the author's views or proposed hypothesis.
1 / 5 (5) Jan 06, 2010
One of the better physorg climate write-ups. Thanks.
1 / 5 (4) Jan 07, 2010
Disagree, good story, but they just had to tie it into Climate Change. If it just ended there that would be fine since there's always climate change, but once they start talking about models predicting the future...
1 / 5 (4) Jan 07, 2010
At first, I thought it was a balanced article as well. But notice that it still emphasizes the role of CO2, which contributes only 3.6% to the total greenhouse effect. Water vapor contributes 95%.

So there is a definite AGW bias in this article as well.

And how many articles has PhysOrg run on Climategate, or from the point of view that AGW is a fraud?
1 / 5 (1) Jan 07, 2010
Disagree, good story, but they just had to tie it into Climate Change. If it just ended there that would be fine since there's always climate change, but once they start talking about models predicting the future...

You're ignoring the fact that the author states that current climate models are useless as they cannot be retroactively fit to the known record. By expanding our knowledge of conditions we can create models that do satisfy recursive reconstruction, therefore being more reasonable regardless of result.
1 / 5 (4) Jan 07, 2010
Notice as well that the article emphasizes the role of CO2 as a greenhouse gas, while CO2 only has a 3.6% contribution to the total greenhouse effect. Water vapor has a 95% contribution. Yes, this article is biased as well.
5 / 5 (2) Jan 07, 2010
Any climate model that fails to "rearcast" past conditions is suspect. So by testing climat models developed for the current climate on past eras, we get an idea of how reliable they are. BTW even if this summary does not go into the role of water vapor, you can count on the underlying study to have included it. It is like an astronomer remembering gravity or a botanist remembering chlorophyll.

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