3.2-Million-Year Temperature History from Tiny Fossils

Aug 05, 2009
Sindia Sosdian (left in helmet) working with core samples on an earlier expedition, while a graduate student at Rutgers

(PhysOrg.com) -- People often talk about greenhouse gases and their effect on the earth's climate as if those effects were new. But greenhouse gases have been around for hundreds of millennia, playing a key role in the start of the ice ages in the Northern Hemisphere 2.72 million years ago.

Yair Rosenthal, a professor of marine science in the Institute of Marine and Coastal Sciences, and Sindia Sosdian, Rosenthal's former student and now a postdoctoral scholar at The Australian National University, have established a 3.2 million-year from the that makes that influence clear.

They also discovered that, beginning about 900,000 years ago, the nature of the ice sheets themselves made ice ages longer and colder. Their findings were published in a recent edition of Science.

Sosdian and Rosenthal demonstrated that progressive cooling of the deep North Atlantic by about 2 degrees Celsius helped bring on the initial Northern Hemisphere ice ages 2.7 million years ago. They also concluded that the way ice sheets grew and shrank influenced the length and intensity of ice ages. Read more about how they came to these conclusions.

The large continental, Northern Hemisphere ice sheets formed on top of relatively loose sediments during what geologists call the Pliocene-Pleistocene Epoch, before 900,000 years ago. These sediments, saturated with meltwater, made the ice sheets resting on them unstable and unable to grow to great heights. About 900,000 years ago, at the middle of the Pleistocene Epoch, successive ice ages had worn away so much that ice sheets were forming on bare bedrock because so much sediment had worn away. The bedrock was very stable, and the ice sheets were able to grow much thicker. The tall ice sheets were able to survive through relatively warm periods between ice ages, and because the ice sheets didn’t decay as quickly, ice ages became longer.

Ice ages typically wax and wane, Rosenthal explained. In the late Pleiocene, the Northern Hemisphere cycled in and out of ice ages every 40,000 years or so. But about 900,000 years ago, the cycle extended to 100,000 years.

"Scientists used to argue about whether those transitional enhancements were associated with major cooling, and if so, why?” Rosenthal said. “But before you had a temperature record, you couldn't really tell. We know now that each of these transitions is associated with a potential cooling of the planet."

Sosdian added that, "We now also know that, although the beginning of ice ages (in the ) is linked to greenhouse gases, the change in intensity is related to how ice sheets grow and decay."

More information: Science paper

Provided by Rutgers, The State University of New Jersey

Explore further: Aging Africa

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User comments : 5

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out7x
1 / 5 (2) Aug 06, 2009
No mention of Milankovitch cycles? Van Houten cycles? Correlation with ice ages?
Birger
4 / 5 (2) Aug 06, 2009
As I interpret the article, the stable, thick ice sheets became more robust and could better survive temporary temperature increases (including those induced by the Milankovitch cycles).
Having grown up in north Sweden, I have often been frustrated by the lack of local fossil sites, as we only have granite bedrock underneath the soil. In fact, even the granite has been badly eroded by the successive glaciations: hills have a distinctive shape with a "lee" side, showing the flow direction of the ice.
Avitar
4 / 5 (1) Aug 06, 2009
An interesting physics problem is to calculate the surfact temperature of a ball with the earths light absorbtion properties at the earth's current distance from the sun. We would never get out of the Snowball Earth mode without greenhouse gases.
omatumr
1 / 5 (2) Aug 06, 2009
REALLY?

1. "Ice ages typically wax and wane, Rosenthal explained. In the late Pleiocene, the Northern Hemisphere cycled in and out of ice ages every 40,000 years or so. But about 900,000 years ago, the cycle extended to 100,000 years."

2. "But greenhouse gases have been around for hundreds of millennia, playing a key role in the start of the ice ages in the Northern Hemisphere 2.72 million years ago."

Really?

Does anything else that might influence Earth's climate "wax and wane" - perhaps like the Earth's heat source? See: "EARTH'S HEAT SOURCE - THE SUN",
Energy and Environment: SPECIAL ISSUE: Natural drivers of weather and climate, volume 20, numbers 1 & 2, pp. 131-144 (2009)
http://arxiv.org/pdf/0905.0704

With kind regards,
Oliver K. Manuel
http://www.omatumr.com/
Ethelred
5 / 5 (1) Aug 07, 2009
REALLY?


Yes, Oliver. Really. Even for you it is strange to pretend that greenhouse are entirely infective.

No one here is claiming the Sun is not a variable. What is being said is the greenhouse gasses are what keeps the Earth warm enough for most of the water to be liquid EVEN when the Sun is at its warmest. Remove the CO2, methane and water vapor and the temperatures would plummet.

Perhaps if you were to actually run the numbers on even YOUR fantasy Sun you might get similar results. After all you think you know the answers and the answers have to fit the evidence. The Earth has had greenhouse gasses since it first had an atmosphere. Back when the Sun was cooler the CO2 levels seem to have higher.

That is over hundreds of millions of years not a few million.

Does you theory show the Sun warming over time? Have you even bothered to figure it out? If it doesn't then it doesn't fit the evidence. Of course that would be only one more miss.

Ethelred