How Plate Tectonics Set the Stage for Civilization in the Eastern Mediterranean

By George W. Moore

Geological Society of the Oregon Country Geological Newsletter, v. 64, p. 30-31 (1998)

The plate-tectonic collision between Africa and Europe had led to approximately the present geography by the time big-brained humans arrived, first the Neanderthals 300,000 years ago, then modern humans 50,000 years ago. Before the humans, during the Age of Dinosaurs, an equatorial "Gulf Stream" from south of Asia had swept into the Pacific and warmed the globe. But then India collided at the Himalaya, and after that Australia moved north to close the remaining gap, and the Earth entered a period of deeping refrigeration.

Minor variations in sunlight hitting the Earth then became critical. They were chiefly caused by the 20,000-year top-like gyration of the spinning Earth, and the 100,000-year hula-hoop rotation of the Earth's solar orbit. These worked together to produce 100,000-year glacial-interglacial stages, each of which gradually became colder during 20,000-year substages, then rebounded abruptly. The Neanderthals lived during the last three glacial-interglacial stages, and modern humans were fully dispersed during the final glacial maximum.

At that time, sea level was as much as 127 meters below its present level, owing to the enormous volume of water tied up in continental ice sheets. Then the rebound came, and the sea rose about 1 meter every 100 years for more than 10,000 years. This flooding swept the hunter-gatherer humans ever higher and prevented them from establishing permanent coastal settlements. At about 4,000 BC, however, the easily melted glacial ice was exhausted, and sea level stabilized. Soon, coastal villages became established, then cities, and finally the trade and culture that we associate with civilization.

The advancing civilizations were next affected more intimately by plate-tectonic processes. A plate boundary that festoons through the eastern Mediterranean had created mineral deposits that fueled art and industry. Cyprus is a seafloor island uplifted where Africa and Europe collide. Erosion there has exposed seafloor pillow lava rich in copper formed at black smokers like those off the coast of Oregon. That copper, combined with tin from granite flanking the Red Sea, provided the raw material for the Bronze Age.

But the beneficial products of plate tectonics, including the metals and the Persian Gulf's petroleum, are countered by two of civilization's greatest terrors--earthquakes and volcanoes. The great plate boundary that courses through the Mediterranean and underlies its adjacent mountains has caused endless disasters. An earthquake likely toppled Jericho's walls and also the bronze Colossus of Rhodes, which stood only 50 years, then lay on the ground for the next 800 years, to be marveled at as one of the Seven Wonders of the World.

Converging tectonic plates shear together at an inclined boundary--a subduction zone. Metal-producing uplifted areas, such as Cyprus, lie on the upper plate close to where the boundary intersects the surface of the Earth. A line of volcanoes marks the surface somewhat farther from the boundary. These volcanoes seem to be caused by water in material carried down on the lower plate into the subduction zone. The water lowers the melting temperature of superheated rock at the base of the upper plate, and melted rock then rises toward the volcanoes.

Such volcanism has been devastating in the Mediterranean region. Ash from Vesuvius buried the Naples suburbs of Pompeii and Herculeum under 6 meters of ash. Earlier, Santorin Volcano north of the Island of Crete exploded catastrophically, ravaging nearby islands and sending out a tsunami that destroyed coastal cities around the Aegean Sea, including Crete's Minoan capital of Knossos.

Indeed, people of the eastern Mediterranean, more than at most places, still need to have measures in place to protect from the hazards of plate tectonics--from earthquakes, volcanoes, and tsunamis.