Bacteria could have plunged the planet into a deep freeze and caused oxygen to dominate the atmosphere, say researchers in America.
The report, from graduate students at the California Institute of Technology, claims that 2.3 billion years ago, blue-green algae gained the ability to break down water which released a flood of oxygen into the atmosphere.
They say the oxygen reacted with the atmospheric methane which insulated Earth at the time, and broke it down, the reaction creating carbon dioxide.
In a process lasting several million years, temperatures plunged to minus 50 degrees Celsius and ice at the equator grew to one mile thick.
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