About two million years ago, the Mediterranean Sea waters stopped being able to reach the basin. The Sodom Lagoon became a landlocked lake that extended from the Sea of Galilee in the north to a point approximately 50 km (30 mi) south of the Dead Sea’s current southern shore. This prehistoric lake, Lake Gomorrah, collected large amounts of sediment on its floor. Because the sediment was heavier than the salt deposits that were there before it, the salt deposits were pushed upwards into geological towers and cliffs like Mount Sodom.
The ensuing epochs saw the lake continue to shrink – first into a smaller lake called Lake Lisan (tongue), and eventually into an even smaller lake, the Dead Sea that we know now. Throughout this period and into our own, the Dead Sea’s water levels have fluctuated dramatically, rising to its highest level around 26,000 years ago. Around 10,000 years ago, the lake’s level dropped dramatically, probably to even lower than today’s.
The Dead Sea is considered the connecting point between the desert and the settled agricultural land of the Middle East (the “Fertile Crescent”). Its surface and shores are 427 metres (1,401 ft) below sea level, Earth’s lowest elevation on land. The Dead Sea is 306 m (1,004 ft) deep, making it the deepest hypersaline lake in the world.
The Dead Sea’s mineral content is nothing like the mineral content of ocean water. Not only is the salinity (saltiness) much greater, but the composition of the salt is much more varied. Whereas the salt in most oceans and seas is approximately 97% sodium chloride (NaCl, or common salt), the salt in the dead sea is only 30% sodium chloride – the rest is calcium chloride (CaC12, 15%), potassium chloride (Kcl, 4%), and magnesium chloride (MgCl, 51%).
The Dead Sea is also surrounded by mineral-rich mud that was deposited by desert runoff streams flowing into the Dead Sea around 10,000 years ago. This gray black mud, abundant on the banks of the sea, contains silicon, calcium, magnesium, iron, potassium, sodium, and titanium oxides, as well as several other compounds in smaller quantities.
The unique mineral content of the Dead Sea water and mud is one of the reasons it has been known as a center for health and relaxation since antiquity.