The Hot Zone

Whiffs of oxygen

Posted by Alison Hawkes on August 24, 2010
Category : Climates of the Past

It’s pretty well accepted among the scientific community that life existed as far back as 3.5 billion years ago. But those were days before oxygen had accumulated to significant levels.What kind of creatures were lurking an an oxygren-free world?

It wasn’t until 2.4 billion years ago during the so-called Great Oxidation Event that  photosynthesizing cyanobacteria (blue-green algae) produced enough oxygen to saturate into organic matter and dissolved iron in the ocean and then more. The free oxygen built up in the atmosphere, killing off a huge number of these anaerobic inhabitants and making room for new species of oxygen-dependent organisms to take over.

But can Earth’s history be so neatly divided into a world before and after oxygen? In a paper published in the journal Nature Geoscience this month, NASA astrobiology researcher Andrew Czaja writes that “whiffs of oxygen” may have been present long before the Great Oxidation Event and would match up with some early oxygen dependent fossils from long ago.

Take for example a kind of manganese-reducing bacteria that might have been present nearly 3 billion years ago. To do its work, it required free oxygen to oxidize manganese. Could there have been a “local oxygen oasis”? Or were there “global oxygen pulses”?

Czaja says that oxygen couldn’t have been widespread at this point because even shallow surface waters were demonstrably anoxic just 200 million years later.

-Alison Hawkes

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