c. 65 Million BCE

The Alps

One effect of the breakup of the Pangean supercontinent around 200 to 150 million years ago was the creation of the mid-Atlantic ridge’s east–west spreading plate boundary and the eventual collision (starting around 65 million years ago) of the African and Eurasian continental plates. As in all major continent–continent collisions since the origin of plate tectonics, the result was the creation of some impressive mountains, including the Alps.

Before Africa and Eurasia collided, a large and deep basin existed between them that harbored the now-gone Tethys Sea. Like any good marine basin, the Tethys Sea collected enormous volumes of limestone and mudstone sediments on its floor, along with salty mineral deposits (evaporites) along its shores. All these rocks and minerals were compressed, folded, metamorphosed, and uplifted as the African and Eurasian plates moved closer over time. Eventually, the Tethys Sea was completely pinched off, and former marine sedimentary deposits were uplifted and stacked together to form the Alps, like a rumpled tablecloth being pushed across a table. Indeed, the thrust blocks making up the Alps are called nappes—French for “tablecloths”—by geologists.

Mountain-building in Europe along the roughly 750-mile (1,200-kilometer) length of the Alps involved a variety of processes, occurring in starts and stops over tens of millions of years. Nappes of metamorphosed sedimentary and volcanic rocks have all been created and mixed by the incessant compressional forces from the colliding continents. Much of the resulting terrain of the Alps is a geologic mess that can be difficult to untangle. The base of the famous Matterhorn peak in Switzerland, for example, consists of ancient metamorphosed Eurasian continental crust, but the tip of the Matterhorn is made of ancient rocks from the African plate. Sandwiched in between the base and the peak are compressed and folded sediments from both Africa and Eurasia that were once laid down in the Tethys Sea.

The mountain-building event or orogeny that created the Alps continues to uplift them today, at a rate estimated to be between 1 millimeter and 1 centimeter per year. Snow, rain, and glaciers erode the mountains down, however, at roughly the same rate.

SEE ALSO Continental Crust (c. 4 Billion BCE), Plate Tectonics (c. 4–3 Billion BCE?), Roots of the Pyrénées (c. 500 Million BCE), The Ural Mountains (c. 320 Million BCE), The Atlas Mountains (c. 300 Million BCE), Pangea (c. 300 Million BCE), The Himalayas (c. 70 Million BCE), Discovering Ice Ages (1837), Birth of Environmentalism (1845)

Summertime view of the rugged and relatively geologically young Italian Alps soaring high above spectacular high mountain lakes.