How Do You Prove a Sea Disappeared?

In the autumn of 1970, a drilling ship pulled a core out of the floor of the deep Mediterranean and brought up the wrong thing. Not the fine grey mud you get on a seafloor — salt. Minerals that only form when seawater evaporates away, from ground that is now kilometres under water. To make them, that seafloor could not have been seafloor at all. The explanation came fast and it was spectacular: the sea was cut off from the Atlantic, dried into a salt desert, and was refilled five and a third million years ago by a single catastrophic flood through Gibraltar. That story has been told for fifty-five years. This video is about what has happened to it since — because the measurements kept getting better, and the story kept getting shakier. Chlorine isotopes now put the drawdown at 1.7 to 2.1 kilometres in the east. That is a staggering number, and it is also not the whole story: the same measurements show the deepest basins never emptied at all, and sea level swung up and down through roughly twenty-nine cycles rather than falling once. The most repeated figure of all — that the sea refilled in about two years — is not a measurement. It is what an erosion model returns when you ask it what kind of flow could have carved the Gibraltar channel. A 2025 review states plainly that the megaflood is "often considered to be a fact", and that several studies suggest Gibraltar may have stayed open the whole time. Whether there was ever a single flood is being argued in the literature right now. 0:00 A core that came up wrong 0:44 Why a quiet seafloor matters 1:33 The story everyone knows 2:09 What is actually measured 3:21 Eighty-three per cent 3:51 It did not happen once 4:35 Three explanations 5:36 Where the famous number comes from 6:25 What is solid, and what is not 7:09 Fifty-five years later Sources: • Aloisi, G. et al. (2024), "Chlorine isotopes constrain a major drawdown of the Mediterranean Sea during the Messinian Salinity Crisis," Nature Communications 15, 9671 — https://doi.org/10.1038/s41467-024-53... • Roveri, M., Lugli, S. & Manzi, V. (2025), "The Desiccation and Catastrophic Refilling of the Mediterranean: 50 Years of Facts, Hypotheses, and Myths," Annual Review of Marine Science 17, 485–509 — https://doi.org/10.1146/annurev-marin... • García-Castellanos, D. et al. (2025), "Kilometric sea level changes during the Messinian salinity crisis caused by river erosion and climate," Science Advances 11(28) — https://doi.org/10.1126/sciadv.ads9752 • García-Castellanos, D. et al. (2009), "Catastrophic flood of the Mediterranean after the Messinian salinity crisis," Nature 462, 778–781 — https://doi.org/10.1038/nature08555 • Micallef, A. et al. (2018), "Evidence of the Zanclean megaflood in the eastern Mediterranean Basin," Scientific Reports 8, 1078 — https://doi.org/10.1038/s41598-018-19... • Micallef, A. et al. (2024), "Land-to-sea indicators of the Zanclean megaflood," Communications Earth & Environment 5, 794 — https://doi.org/10.1038/s43247-024-01... • (2025), "Transient oxygenation of the Mediterranean after the Zanclean megaflood," PNAS — https://doi.org/10.1073/pnas.2505429122 • (2022), "Limited Mediterranean sea-level drop during the Messinian salinity crisis inferred from the buried Nile canyon," Communications Earth & Environment — https://doi.org/10.1038/s43247-022-00... #geology #mediterranean #earthscience