Climate change and the rise of atmospheric oxygen (Forwarded)

Carnegie Institution of Washington
Washington, D.C.

Carnegie contacts:

Shuhei Ono, 202-478-8988
Andrey Bekker, 202-478-7974
Doug Rumble, 202-478-8990

March 22, 2006

Climate change and the rise of atmospheric oxygen

Washington, D.C. -- Today's climate change pales in comparison with what
happened as Earth gave birth to its oxygen-containing atmosphere billions
of years ago. By analyzing clues contained in rocks, scientists at the
Carnegie Institution's Geophysical Laboratory have found that the initial
rise of oxygen (O2) was transitory and that its final emergence may have
been linked to volcanoes and catastrophic glaciations. The work is
presented in several talks at NASA's Astrobiology Science Conference
(AbSciCon) 2006 at the Ronald Reagan Building in Washington, D.C., March
26-30. See http://abscicon2006.arc.nasa.gov/ for details.

"Rocks contain fingerprint-like clues to the past environment through
specific variations in elements such as sulfur," explained Carnegie
researcher Shuhei Ono. [1] "Our Earth didn't start out with oxygen in the
atmosphere. It probably contained methane and hydrogen, but no oxygen. We
think that there were microbes in the oceans, before the oxygenated
atmosphere, which would have used methane for energy. Measuring sulfur
isotopes -- different versions of the atom with the same number of
protons, but a different number of neutrons -- in rock samples provides a
sensitive way to monitor ancient oxygen levels. Oxygen first appeared on
the surface of the Earth when microbes developed the capacity to split
water molecules to produce O2 using the Sun's energy. This is a bit
advanced biochemistry, but we think this biological revolution emerged
sometime before 2.7 billion years ago," he continued.

Ono looked at sulfur isotopes from South African drill-core samples
covering the time interval from 3.2 to 2.4 billion years ago. Around 2.9
billion years ago, the methane-dominated atmosphere provided a greenhouse
effect and kept the planet warm. His analysis suggests that when oxygen
first appeared in the atmosphere, around that time, it would have reacted
with the methane, destabilizing the atmosphere and triggering the
Mozaan-Wi****ersrand glaciation.

The oxygen atmosphere wasn't here to stay, however. "It was a raucous
time," stated Carnegie's Andrey Bekker. [2] "Volcanoes peppered the
Earth's surface, belching gases and particulates into the atmosphere. That
material rained back to the surface and oceans, affecting ocean chemistry
and the ocean and atmospheric cycles. We looked at sulfur isotopes in
shale and pyrite from Western Australia and found that between 2.47 and
2.463 billion years ago oxygen levels started to rise. But the intense
volcanic activity made it almost disappear again. Despite these fits and
starts, our oxygen atmosphere prevailed in the end."

Talks and poster schedule subject to change. See
http://abscicon2006.arc.nasa.gov/agenda.php for the latest information.

[1] Shuhei Ono, "A novel record of Earth's Archean life, atmosphere, and
oceans revealed in multiple-sulfur isotopic signatures"Tuesday, March
28th, 11:30 am
Reagan Center, Amphitheater, Mini-Key II Early Earth

[2] Andrey Bekker et al., "A fitful rise of atmospheric oxygen" Wednesday,
March 29th, 4:40 pm
Reagan Center, Polaris B conference room, Session 29: Sulfur on Earth and
Mars II

Olivier Rouxel et al., "Record of hydrothermal plume process in
Paleoproterozoic jasper and iron formation: implications for the redox
state of the 1.74 Ga deep ocean"
Monday March 27th, 5:20 pm
Reagan center, Horizon A conference room, Session 7: Environmental Impact
of Life

Olivier Rouxel and Andrey Bekker, "New insights into Precambrian ocean
chemistry from coupled iron & sulfur isotope analyses"Poster displayed
throughout the conference. Poster session Monday night, March 27th 6:00 pm
to 8:00 pm Reagan Center, Atrium Hall.

The Carnegie Institution of Washington (www.CarnegieInstitution.org) has
been a pioneering force in basic scientific research since 1902. It is a
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the U.S. Carnegie scientists are leaders in plant biology, developmental
biology, astronomy, materials science, global ecology, and Earth and
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This work is supported by the NASA Astrobiology Institute (NAI). The NAI,
founded in 1998, is a partnership between NASA, 16 major U.S. teams and
six international consortia. NAI's goal is to promote, conduct, and lead
integrated multidisciplinary astrobiology research and to train a new
generation of astrobiology researchers. For more information about the NAI
on the Internet, visit:
http://nai.nasa.gov/