An entire sea vanished — then came back in under two years, in the largest flood the planet has ever seen. This is the Messinian Salinity Crisis and the Zanclean megaflood, told from the salt on the seafloor up. Around 5.97 million years ago the Mediterranean was cut off from the Atlantic. Under a brutal sun it evaporated faster than its rivers could refill it, dropping as much as two kilometres and losing up to 80% of its water.

For a while you could have walked from Africa to Europe across a salt desert three kilometres below sea level. Then, around 5.33 million years ago, the Atlantic broke through at Gibraltar — a kilometre-tall waterfall pouring roughly 100 million cubic metres of water every second, about a thousand Amazons, refilling 90% of the basin in a matter of months. Nothing that emptied it has stopped. Africa is still pushing north. The gate at Gibraltar will be closing again.