The Mediterranean Sea: birthplace of European civilization, and still its favorite vacation spot. You’d never know that, not too long ago, it was a desert filled with salt, with temperatures over 150 degrees.

About 6 million years ago, growing ice sheets in Antarctica began to trap Earth’s water and lower sea levels. Waters in the Strait of Gibraltar, that narrow channel between Spain and Morocco, began to recede.

Freed from the weight of the water, the land began to rise. Which caused a feedback loop of shallower waters and more rising seafloor, till the strait … became a dam, and the Mediterranean was separated from the Atlantic.

Within a thousand years, the Mediterranean had almost completely dried up, leaving a desert basin nearly 2 miles deep. Over several hundred thousand more years, it was partially filled and dried out again many times, leaving layers of salt and gypsum, in some places more than a mile thick.

Around 5 and a half million years ago, the major ice sheets began to melt, and a rising Atlantic breached the dam. Water rushed into the Mediterranean, carving a channel a mile wide and 100 miles long.

Scientists estimate it filled the entire Mediterranean again in less than 2 years, and in short order, one of the Earth’s most inhospitable places became one of its richest, teeming with life.