Research
Earth’s Oceans: Where Was the Oxygen?
As two rovers scour Mars for signs of water and the precursors of life, Rochester
geochemists have uncovered evidence that Earth’s own ancient oceans were
much different from today’s.
The research, published in the journal Science, cites new data that
shows that Earth’s life-giving oceans had less oxygen dissolved in them
than today’s and could have been nearly devoid of oxygen for a billion
years longer than previously thought. The findings may help explain why complex
life barely evolved for billions of years after it arose.
The Rochester team has pioneered a new method that indicates how ocean oxygen
might have changed globally. Most geologists agree that there was virtually
no oxygen dissolved in the oceans until about 2 billion years ago, and that
they were oxygen-rich during most of the last half billion years—but there
has always been a mystery about the period in between. Geochemists developed
ways to detect signs of ancient oxygen in particular areas, but not in the Earth’s
oceans as a whole. The team’s method, however, can be extrapolated to
grasp the nature of all oceans around the world.
“This is the best direct evidence that the global oceans had less oxygen
during that time,” says Gail Arnold, a doctoral student in earth and environmental
sciences at the University and lead author of the research.
Arnold examined rocks from northern Australia that were at the floor of the
ocean over a billion years ago, using the new method developed by her and her
coauthors, Jane Barling of the University of British Columbia and Ariel Anbar,
associate professor of earth and environmental sciences.
Previous researchers had drilled down into the rock and tested its chemical
composition, confirming it had preserved original information about the oceans.
The Rochester team brought the rocks back to their labs where they used newly
developed technology—called a Multiple Collector Inductively Coupled Plasma
Mass Spectrometer—to examine the chemistry of the rocks.
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