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Sci Tech
Earth’s oxygen more ancient than first believed
A group of scientists from various universities have discovered that oxygen appeared first in Earth’s atmosphere about 50 to 100 million years earlier than was previously believed. Drilling deep into the earth’s crust they extracted a kilometre-long core of sedimentary rock.
Trace metal amounts
They analyzed the amounts of the trace metals molybdenum, rhenium and uranium in the sediment. The amounts of these metals in oceans and sediments depend on the amount of oxygen in the environment.
Analyzing the layers of sedimentary rock in the sample the researchers report finding evidence that a small but significant amount of oxygen — a whiff — was present in the oceans and possibly Earth’s atmosphere 2.5 billion years ago.
The data also suggest that oxygen was nearly undetectable just before that time. For the first half of Earth’s 4.56-billion-year history, the environment held almost no oxygen, other than bound to hydrogen in water (H{-2}O) or to silicon and other elements in rocks.
Then, some time between 2.3 and 2.4 billion years ago, oxygen rose sharply in the Earth’s atmosphere and oceans. Scientists call this the Great Oxidation Event.
The scientists analyzed the drill core for geochemical and biological tracers representing the time just before the rise of atmospheric oxygen.
Rock samples
Using state-of-the-art facilities and instruments in Arizona State University’s W.M. Keck Foundation Laboratory for Environmental Biogeochemistry, Scientist Ariel Anbar and fellow researchers took rock samples from the core and pummelled them to powders, dissolved the powders in acid and vaporized the acid solutions for analysis, using an inductively coupled plasma mass spectrometer, according to an Arizona State University press release.
The goal
Their goal was to characterize the nature of the environment and life in the oceans leading up to the Great Oxidation Event.
Alan Jay Kaufman, studying the chemistry of sulphur from the same samples began seeing funny variations in the chemistry of sulphur. Doctoral student at ASU, Yun Duan, sped up the research to see for variations in metal abundances in the same places – and did see such variations.
One explanation is that the ancient ancestors of today’s plants first began to produce oxygen by photosynthesis at this time. — Our Bureau
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