Past sea level has varied by somewhat more than a hundred metres. This is primarily due to the growth and decay of ice sheets (mostly in the northern hemisphere) with water evaporated from the sea. The Mediterranean Basin's gradual growth as the Neotethys basin, begun in the Jurassic, did not suddenly affect ocean levels. While the Mediterranean was forming during the past 100 million years, the average ocean level was generally 200 metres above current levels. However, the largest known example of marine flooding was when the Atlantic breached the Strait of Gibraltar at the end of the Messinian Salinity Crisis about 5.2
Sea level rise literature found estimates for the Greenland ice sheet and its glaciers and ice caps, they were the largest contributor to the observed sea level rise from "land ice" sources (excluding thermal expansion), combined accounting for 71 percent, or 1.32 mm per year during the 2012–2016 period. Mountain glaciers include only a minor fraction of all water bound up in glaciers ice (<1%), compared to a bigger portion in Greenland and Antarctica (99%). Still, mountain glaciers have contributed appreciably to historical sea level rise and are set to contribute a smaller, but still significant fraction of sea level rise in the