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
Normal height Normal height Normal heights are heights above sea level, one of several types of height which are all computed slightly differently. Alternatives are: orthometric heights and dynamic heights. The normal height formula_1 of a point is computed from geopotential numbers by dividing the point's geopotential number, i.e. its geopotential difference with that of sea level, by the average, normal gravity computed along the plumbline of the point. (More precisely, along the ellipsoidal normal, averaging over the height range from 0 — the ellipsoid — to formula_1; the procedure is thus recursive. Normal heights are thus dependent upon the reference ellipsoid