Geology

Geologically, the Mediterranean is a shrunken remnant of the Tethys Ocean, an immense tropical sea that existed in the Mesozoic Era more than 63 million years before our time. Over millions of years, plate tectonics moved Africa northward toward Eurasia, the continental plates collided and in the Aegean sector, the African continental plate began to slip under the European plate. As one result, the mountain ranges of Greece folded upward in a complex pattern. The chain of Pindos, the backbone of northern Greece, and Olympos, the highest mountain in Greece at 2,917 m, are among the results of this folding. The process continues today and is a reason why Greece has been an active earthquake zone throughout human history. Along with the folding, volcanic activity occurred and still occurs intermittently in the Aegean island arc at places such as Thera (Santorini), Nisyros, and Methana. There are many other sites of past volcanic activity, such as the islands of Melos, Lesbos, and Lemnos. In the late Tertiary Period, the Strait of Gibraltar closed and the

Mediterranean slowly evaporated, leaving saline lakes and deep salt beds behind. This probably happened several times. Remains of the products of evaporation can be seen in many locations because geologic uplift has raised former shorelines high above the present sea level in Cyprus, for example, and the Ionian islands. Then about 5.5 million years ago, the Atlantic found its way through the strait and filled the Mediterranean. Greece was not covered by the Ice Age glaciation, but the climate cooled, precipitation increased, and evaporation slowed. Evidence of valleys carved by large mountain glaciers is found on Olympos and other massifs such as the Pindos and Rhodope mountains.

The oldest rocks in Greece are fragments of the ancient continental plates dating back to the Precambrian era which are found in the mountains of Thrace and eastern Macedonia. The more prevalent and extensive strata are of limestone originally laid down as sediment under the Tethys Ocean. This limestone, under geologic pressure, has been formed into fine marble in places such as the islands of, e. g., Paros and Thasos. Other sedimentary formations such as sandstone, shale, and conglomerate exist. In the zones of volcanic activity, igneous rocks are evident. From surface rocks the process of soil formation began with the aid of vegetation; while there are limited areas of highly fertile soil in Greece, over much of the country soils are thin and poor.