Scientists Find Evolution of Life Helped Keep Earth Habitable (Forwarded)

Lawrence Livermore National Laboratory

Contact: Anne Stark
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FOR IMMEDIATE RELEASE: October 30, 2003

NR-03-10-07

Scientists Find Evolution of Life Helped Keep Earth Habitable

LIVERMORE, Calif. -- A trio of scientists including a researcher from the
Lawrence Livermore National Laboratory has found that humans may owe the
relatively mild climate in which their ancestors evolved to tiny marine
organisms with shells and skeletons made out of calcium carbonate.

In a paper titled "Carbonate Deposition, Climate Stability and Neoproterozoic
Ice Ages" in the Oct. 31 edition of Science, UC Riverside researchers Andy
Ridgwell and Martin Kennedy along with LLNL climate scientist Ken Caldeira,
discovered that the increased stability in modern climate may be due in part to
the evolution of marine plankton living in the open ocean with shells and
skeletal material made out of calcium carbonate. They conclude that these marine
organisms helped prevent the ice ages of the past few hundred thousand years
from turning into a severe global deep freeze.

"The most recent ice ages were mild enough to allow and possibly even promote
the evolution of modern humans," Caldeira said. "Without these tiny marine
organisms, the ice sheets may have grown to cover the earth, like in the
snowball glaciations of the ancient past, and our ancestors might not have
survived."

The researchers used a computer model describing the ocean, atmosphere and land
surface to look at how atmospheric carbon dioxide would change as a result of
glacier growth. They found that, in the distant past, as glaciers started to
grow, the oceans would suck the greenhouse gas -- carbon dioxide out of the
atmosphere -- making the Earth colder, promoting an even deeper ice age. When
marine plankton with carbonate shells and skeletons are added to the model,
ocean chemistry is buffered and glacial growth does not cause the ocean to
absorb large amounts of carbon dioxide from the atmosphere.

But in Precambrian times (which lasted up until 544 million years ago), marine
organisms in the open ocean did not produce carbonate skeletons -- and ancient
rocks from the end of the Precambrian geological age indicate that huge glaciers
deposited layers of crushed rock debris thousands of meters thick near the
equator. If the land was frozen near the equator, then most of the surface of
the planet was likely covered in ice, making Earth look like a giant snowball,
the researchers said.

Around 200 million years ago, calcium carbonate organisms became critical to
helping prevent the earth from freezing over. When the organisms die, their
carbonate shells and skeletons settle to the ocean floor, where some dissolve
and some are buried in sediments. These deposits help regulate the chemistry of
the ocean and the amount of carbon dioxide in the atmosphere. However, in a
related study published in Nature on Sept. 25, 2003, Caldeira and LLNL physicist
Michael Wickett found that unrestrained release of fossil-fuel carbon dioxide to
the atmosphere could threaten extinction for these climate-stabilizing marine
organisms.

Founded in 1952, Lawrence Livermore National Laboratory is a national security
laboratory, with a mission to ensure national security and apply science and
technology to the important issues of our time. Lawrence Livermore National
Laboratory is managed by the University of California for the U.S. Department of
Energy's National Nuclear Security Administration.