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There have been five major die-offs, in which thousands of species were wiped out from the planet. Paleontologists still argue over the possible causes, with meteorite impacts, super volcano eruptions, changes of sea level and other catastrophic events named as possible culprits.
James Castle and John Rodgers of Clemson University put the blame on microscopic algae, which produce toxins and consume oxygen. In their work, presented at the annual meeting of the Geological Society of America in Portland, the scientists reported their findings of spikes in the number of algae fossils - stromatolite structures - coinciding with mass extinctions of the past.
