Historical Geology Understanding Our Planet\'s Past

warm Pacific currents, this might have initiated the Pleistocene glacial epoch.

Never before have permanent ice caps existed at both poles, suggesting that

the planet has been steadily cooling since the Cretaceous.

CLOSING OF THE TETHYS

The Tethys Sea was a large, shallow equatorial body of water that linked the

Indian and Atlantic Oceans. It separated the southern and northern continents

during the Mesozoic and early Cenozoic. About 17 million years ago, the

Tethys began to close off as Africa rammed into Eurasia, creating the Mediter-

ranean, Black, Caspian, and Aral Seas (Fig. 189). The collision also initiated a

major mountain building episode that raised the Alps and other ranges. The

climates of Europe and Asia were warmer. Forests were more widespread and

lusher than today.

The Mediterranean Basin was apparently cut off from the Atlantic

Ocean 6 million years ago. An isthmus, created at Gibraltar by the northward

movement of the African plate, formed a dam across the strait. Nearly 1 mil-

lion cubic miles of seawater evaporated, almost completely emptying the basin

over a period of about 1,000 years.The adjacent Black Sea, at 750 miles long

and 7,000 feet deep, might have had a similar fate. Like the Mediterranean, it

is a remnant of an ancient equatorial sea that separated Africa from Europe.

The collision of the African plate with the Eurasian plate squeezed out

the Tethys. This resulted in a long chain of mountains and two major inland

seas, the ancestral Mediterranean and a composite of the Black, Caspian, and

Figure 189The closing of
the Tethys Sea by the
collision of Africa with
Europe and Asia about 20
million years ago, creating
the Mediterranean, Black,
Caspian,and Aral Seas.

Historical Geology

AFRICA

EUROPE

Tet

hys Sea

Atlantic

Ocean