With an area of about 2.500.000 square km, the Mediterranean Sea occupies roughly 1% of the Earth’s water surface.
The geological formation of the Mediterranean Sea has extremely ancient origins and is the result of a particularly complex evolution. At the end of the Miocene (6–7 million years ago), an important episode in the geological history of the Mediterranean Sea occurred: the progressive advancement of the African continent towards the European landmass closed the Strait of Gibraltar, which was the connection to the Atlantic Ocean; in this way the Mediterranean Sea became in a very short time tan enormous saltwater lake.
The closure of the link with the Atlantic Ocean caused what we now call the “Messinian Salinity Crisis”, during which the Mediterranean Sea suffered a severe hydrological deficit, with the consequent deposit of vast quantity of minerals, almost as if it were an enormous saltpan.
The crisis lasted for less than 1 million years, but this was long enough to create enormous deposits of “evaporates” with great thickness, that can still be found today beneath the most recent sediment deposits. The Mediterranean Sea has now an average depth of 1.370 metres, reaching its deepest point at 5.120 metres to the south of Greece.
The exchange of water through the Strait of Gibraltar, just 13 km wide and about 300 metres deep, is very slow. Surface waters are exchanged every 80–90 years, and it is estimated that the sea’s entire volume is renewed over a period of about 7.500 years.
Thanks to its rich biodiversity of life-forms, the Mediterranean Sea - one of the main eco-regions of the Earth - is one of its most important ecosystems of the World.
The Mediterranean’s natural environment is a combination of homogeneous geomorphologic and climatic factors, and its biological diversity is due principally to the adaptation of many species to the hot, dry summers and mild winters of our climate. An important contribution to the sea’s richness of biodiversity also comes from the high primary productivity caused by movements of cold water masses in the Mediterranean basin:
in this area the wind and the currents redistribute nutritional substances in the water column, making them available for planktonic organisms, that are the first link in the marine food chain.
Antropic effect on he Mediterranean coasts, characterized by the exponential increase of population and production activities over the last century, has led to a progressive decrease in biodiversity, a phenomenon amplified by the fact that the Mediterranean is a semi-enclosed sea with a very slow exchange of its waters.