NASA Research Indicates Oxygen on Earth 2.5 Billion Years Ago



NASA-funded astrobiologists have found evidence of oxygen present in Earth's atmosphere earlier than previously known, pushing back the timeline for the rise of
oxygen in the atmosphere. Two teams of researchers report that traces of
oxygen appeared in Earth's atmosphere from 50 to 100 million years before
what is known as the Great Oxidation Event. This event happened between 2.3
and 2.4 billion years ago, when many scientists think atmospheric oxygen
increased significantly from the existing very low levels.
Scientists analyzed a kilometer-long drill core from Western Australia,
representing the time just before the major rise of atmospheric oxygen.
They found evidence that a small but significant amount of oxygen was
present in Earth's oceans and atmosphere 2.5 billion years ago. The
findings appear in a pair of research papers in the Sept. 28 issue of the
journal Science.
"We seem to have captured a piece of time during which the amount of
oxygen was actually changing -- caught in the act, as it were," said Ariel
Anbar, an associate professor at Arizona State University, Tempe, and
leader of one of the research teams.
The goal of both research teams was to learn more about the environment
and life in the oceans leading up to the Great Oxidation Event. The
researchers did not expect to find evidence of oxygen earlier than what was
previously known.
"The core provides a continuous record of environmental conditions,
analogous to a tape recording," explained Anbar. He and his research group
analyzed the amounts of the trace metals molybdenum, rhenium and uranium.
The quantity of these metals in oceans and sediments depend on the amount
of oxygen in the environment. The other research group, led by Alan Kaufman
of the University of Maryland, College Park, Md., analyzed sulfur isotopes.
Its distribution also relies on the abundance of oxygen.
"Studying the dynamics that gave rise to the presence of oxygen in
Earth's atmosphere deepens our appreciation of the complex interaction
between biology and geochemistry," said Carl Pilcher, director of the NASA
Astrobiology Institute at NASA's Ames Research Center, Moffett Field,
Calif., which co- funded the study. "Their results support the idea that
our planet and the life on it evolved together."
One possible explanation for the Great Oxidation Event is the ancient
ancestors of today's plants first began to produce oxygen by
photosynthesis. However, many geoscientists think organisms began to
produce oxygen much earlier, but the oxygen was destroyed in reactions with
volcanic gases and rocks.
"What we have now is new evidence for some oxygen in the environment 50
to 100 million years before the big rise of oxygen," Anbar said. "Our
findings strengthen the notion that organisms learned to produce oxygen
long before the Great Oxidation Event, and that the rise of oxygen in the
atmosphere ultimately was controlled by geological processes."
The international project brought together researchers from Arizona
State University, the University of Maryland, the University of Washington,
the University of California, Riverside, and the University of Alberta. The
project received financial support from the NASA Astrobiology Institute and
the National Science Foundation. The Geological Survey of Western Australia
provided logistical support.
Founded in 1998, the NASA Astrobiology Institute is a partnership
between NASA, 16 U.S. teams and five international consortia to promote,
conduct and lead integrated multidisciplinary astrobiology research and
train a new generation of astrobiology researchers. The institute's
Astrobiology Drilling Program is an international program aimed at
coordinating continental drilling projects of astrobiological significance,
especially those concerning Earth's early atmosphere.