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
Water distribution on Earth a globally significant amount of water. "Saline" groundwater is seldom considered except when evaluating water quality in arid regions. The remainder of the Earth's water constitutes the planet's "fresh water" resource. Typically, fresh water is defined as water with a salinity of "less than 1 percent that of the oceans" - i.e. below around 0.35‰. Water with a salinity between this level and 1‰ is typically referred to as "marginal water" because it is marginal for many uses by humans and animals. The ratio of salt water to fresh water on Earth is around 40 to 1. The planet's fresh