Hints: France Rhone Valley the Grand Canyon Morocco the Rock of Gibraltar Atlantic The Mediterranean

Just a few million years ago, France's Rhone Valley must have looked more like the Grand Canyon. So intense was the heat in the basin that these waterfalls evaporated before they even reached the old seafloor. For tens of thousands of years, a natural dam between present-day Morocco and the Rock of Gibraltar held the waters of the Atlantic bay. The Mediterranean basin remained an almost lifeless expanse of salt, sand and parched earth. But as Africa pushed and pulled Europe's southern boundary, the pressures on the crust became unbearable. Rising tides weakened the land bridge and then the Atlantic burst its way over the precipice. So began the most gigantic flood ever. At its peak, enormous waterfalls a thousand times grander than Niagara thundered into the basin. More than 100 cubic kilometers of water gushed past Gibraltar every day.

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