Carnegie Institution of Washington
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.  "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
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-Witwatersrand glaciation.
The oxygen atmosphere wasn't here to stay, however. "It was a raucous
time," stated Carnegie's Andrey Bekker.  "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.
 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
 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
private, nonprofit organization with six research departments throughout
the U.S. Carnegie scientists are leaders in plant biology, developmental
biology, astronomy, materials science, global ecology, and Earth and
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
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