I knew the Mediterranean Sea was once landlocked, and flooded a few million years ago via the Strait of Gibraltar, but I never stopped to think about what this meant.
Prior to the sea flooding, it had been cut off from the ocean and gradually dried up over a few million years. This meant that, despite rivers from Southern Europe and the Nile flowing into it, evaporation happened faster than the sea could be replenished. The surface under the sea, as it turns out, was very deep in parts. Geologists believe that the lowest patch of dry land at this time was around 12,500 feet below sea level, an elevation unheard of in the modern world. As you descend, the air becomes denser and hotter. Scientists estimate that summertime high temperatures at this level would have reached around 176F / 80C, with a pressure of 1.45-1.7 atmospheres. At the very bottom there were briny lakes formed from the output of the Nile and other rivers. The lakewater would have been extremely hot and extremely salty. Death valley? More like vast gaping chasm of extinction, a place too hostile for nearly all creatures to survive.
Hell on Earth existed.
The flood that refilled the sea may have been cataclysmic and extremely rapid. Given the upside-down-mountainous nature of the sea, water may have had a chance to reach a very high velocity in a very large volume as it cascaded down steep slopes, creating a level of power and violence none of us are likely to ever see.