The Red Sea was formed by Arabia splitting from Africa due to movement of the Red Sea Rift. This split started in the Eocene and accelerated during the Oligocene. The sea is still widening and it is considered that the sea will become an ocean in time (as proposed in the model of John Tuzo Wilson).
Sometimes during the Tertiary period the Bab el Mandeb closed and the Red Sea evaporated to an empty hot dry salt-floored sink. Effects causing this would be:
A "race" between the Red Sea widening and Perim Island erupting filling the Bab el Mandeb with lava.
The lowering of world sea level during the Ice Ages due to much water being locked up in the ice caps.
Today surface water temperatures remain relatively constant at 21 25 °C (70 77 °F) and temperature and visibility remain good to around 200 m (656 ft), but the sea is known for its strong winds and unpredictable local currents.
In terms of salinity, the Red Sea is greater than the world average, approximately 4 percent. This is due to several factors:
High rate of evaporation and very little precipitation.
Lack of significant rivers or streams draining into the sea.
Limited connection with the Indian Ocean, which has lower water salinity.
A number of volcanic islands rise from the center of the sea. Most are dormant, but in 2007 Jabal al-Tair island erupted violently