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
Mother Earth Water Walk Mother Earth Water Walk Mother Earth Water Walk is an Anishinaabe led initiative dedicated to raising awareness about the importance of water and the need for protection of water. Organizers and participants have walked around bodies of water since 2003 as a way of taking action against water pollution. In 2003 Anishinaabe grandmothers, including Grandmother Josephine Mandamin, along with many Anishinaabe women and men, began walking around the Great Lakes on Turtle Island. They came together to raise awareness about society's negligence towards water. In 2011 a Health Canada study found that 122 First Nation communities were under water advisories.