OXYGEN may be the breath of life, but it’s not entirely clear how Earth’s atmosphere came to be so full of it. Now it seems that supercontinents and supermountains played a major role in the process.
The oxygenation of Earth’s atmosphere is thought to have happened in six or seven steps, starting 2.65 billion years ago and ending about 40 million years ago. Ian Campbell and Charlotte Allen of The Australian National University in Canberra say that most of these steps coincide with the formation of supercontinents such as Gondwana and Pangaea.
The tectonic collisions that led to supercontinents also formed supermountains, which eroded rapidly, washing vast amounts of nutrients into the oceans, fuelling explosions of oxygen-producing algae and bacteria, they say.
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The team established the link by dating the zircon crystals from major river deltas. Zircon, they believe, crystallised from the magma that formed when Earth’s crust melted during the collisions (Nature Geoscience, ).
The massive sedimentation during these periods could also have buried organic carbon and pyrite, which react with oxygen, allowing oxygen to accumulate more quickly in the atmosphere.
But geochemist Dick Holland of Harvard University says there was no tectonic upheaval during the so-called great oxidation event around 2.3 billion years ago. “This virtually destroys their proposed connection between continental collisions and oxygen levels,” he says.
