The Earth has endured many mass extinctions.  We are pretty confident that we know what caused these events.  Except for one of them: the one at the end of the Devonian period 360 million years ago.  John Marshall is a fossil expert specializing in mass extinction events and is a Professor at the School of Ocean & Earth Science at the University of Southampton.  He explains how his recent research has uncovered new evidence that may finally explain what caused the end-Devonian mass extinction.
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