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Terres Noires, France/Mountains

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Terres Noires, France/Mountains

These dark layers of the Terres Noires, which means black earth, are widespread in the French Alps. They developed in a deep sea basin whose oxygen content  varied. When there was less oxygen in the water, dead marine organisms could not completely decompose and as a result their remains coloured the sediment dark. In the oxygen-rich water, the organic substance was able to fully decompose and deposits of bright limestone were formed. (aerial view)