This irregularity of the DEMF path plus an increasing number of ambiguities, related to similarity of the DEMF at different times further into the past, are the most serious limitations of the method.Though well-dated eruptions are known for the last two millennia, retrieval of their products is often misleading and about 50% of volcanics presumed of known date prior to the 17th century are in fact of older age, discrepancies usually reaching several hundreds of years.Age determination is based upon similarity between variation curves of the Direction of Earth’s Magnetic Field (DEMF) reconstructed in France from 120 well-dated archeological sites, and on Italian volcanoes from historically dated eruptions.A total of 63 lava flows and pyroclastic units, such as cinder cones or nuée ardente deposits, are shown to be dated with an overall precision of ±40 years for the last 1500 years, and ±50 to ±100 years from AD 500 to 150 BC, this lesser precision resulting from both an increasing uncertainty on the shape of the DEMF curve and a smaller variation of the DEMF itself.Instead, about 5 million years ago the seafloor consisted of several basins of variable size and topography, with depths ranging from 650 to 5,000 feet (200 to 1,500 metres).Highly saline waters of greatly varying depth probably covered the bottom and deposited salts.The Aegean Sea contains the numerous islands of the Grecian archipelago.The Adriatic Sea, northwest of the main body of the eastern Mediterranean Sea, is bounded by Italy to the west and north and by Slovenia, Croatia, Bosnia and Herzegovina, Montenegro, and Albania to the east.seafloor spreading that have been undertaken since the late 20th century, however, have suggested that the present Mediterranean seafloor is not part of the older (200 million years) Tethys floor.
The widest continental shelf is off Spain at the Ebro River delta, where it extends about 60 miles (95 km).
Considerable uncertainty has remained regarding the chronology and character of sea-bottom salt formation, and evidence from subsequent seismic studies and core sampling has been subject to intense scientific debate.
Strait of Messina, both of which have been of great strategic importance throughout Mediterranean history.
The structure and present form of this tectonically active basin and its bordering mountain system have been determined by the convergence and recession of the relatively stable continental plates of Eurasia and Africa during the past 44 million years.
The interpretation of geologic data suggests that there are, at present, multiple main areas of collision between Africa and Eurasia, resulting in volcanism, mountain building, and land submergence.seabed sediment cores drilled in 19 initially seemed to reinforce an earlier theory that about 6 million years ago the Mediterranean was a dry desert nearly 10,000 feet (3,000 metres) below the present sea level and covered with evaporite salts.