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Story of Earth: The Tethys Sea

Mediterranean Sea
The Mediterranean Sea looking west from the Triassic Period marine rocks uplifted to form the island of Corfu in northwest Greece

Where is the Tethys Sea? I was lucky enough to spend time on one of the last vestiges of the Tethys Sea this summer as a heat wave baked the land and sea and me. I floated in the bathtub-warm salty waters on the edge of a once-ocean, knowing that beneath me was the oldest oceanic crust still residing beneath the waves. For millions of years before it was a sea it was an ocean, and it encircled the entire Earth. So why don't people know about it today? We call the last remaining vestiges of the Tethys the Mediterranean, Black, Caspian, & Aral Seas.

The Tethys Ocean dominated the tropical latitudes for the majority of the last half billion years. As it changed shape and size iterations of its existence are described as the Proto-Tethys Ocean, the Paleo-Tethys Ocean, the Tethys Ocean, the Paratethys, the Neo-Tethys, and the Tethys Sea. Tethys is named after an ancient Greek sea goddess, a Titan and daughter of deities. Tethys mother was Gaia, the personification of Earth. Tethys father (and brother) was Uranus, the personification of the sky. Tethys married her brother Oceanus, the personification of the great river that encircled the world.

Approximately 600 millions years ago the Proto-Tethys Ocean opened as divergent tectonic boundaries in the ocean floor widened the oceanic crust, forcing the continents further apart. During the Cambrian Period, as the first animals with skeletons and eye balls roamed the ocean floors, the Tethys Ocean grew.

Pangaea supercontinent map
Pangaea Supercontinent during the Triassic Period ~200 million years ago

As Pangaea supercontinent formed the Tethys Ocean lay to the east of the growing supercontinent. As Pangaea dissembled during the time of the Dinosaurs, the Tethys grew once again. Pangaea broke into 2 pieces, the northern continent called Laurasia and the southern continent called Gondwana. The Tethys wrapped around Earth, a band of equatorial waters that witnessed the evolution of the Mesozoic Era (252-66 million years ago) marine reptiles like Plesiosaurs and Ichthyosaurus, and harbored the Cenozoic Era (66-0 million years ago) evolution of Whales and Sea Cows.

Earth map of 65Ma
Neo-Tethys Ocean 65 million years ago

Over the last 50 million years the Tethys began to close as the Indian and Atlantic Oceans opened. Over millions of years the Tethys shrank as the ocean floor plunged into the deep earth in a process called tectonic subduction. India moved northward towards Asia, closing the eastern Tethys. Rocky remnants of the ancient Tethys and fossils of its long ago marine inhabitants are preserved in the Himalayan Mountains that formed as the Tethys ocean floor was broken and uplifted to form the mountains.

Tethy's evolution over 65Ma
Earth's tectonics evolution over the least 65 million years

Africa continues to move northward closing the western Tethys as it collides with Europe. The ancient equatorial ocean was squeezed until land enclosed it, forming a sea that marked the end of oceanic existence. Some pieces of the once great ocean became entirely cut off from the oceans of the world, evolving into the seas we now call the Caspian Sea, Black Sea, and Aral Sea.

Mediterranean Sea
Cretaceous Period marine rocks on the shore of the Mediterranean Sea off the southeast coast of Italy near Brindisi

The Mediterranean Sea is the last remnant of the Tethys Sea that is still connected to an ocean. The Tethys seafloor that lies beneath the waters of the Mediterranean Sea is 340-280 million years old. It formed when the divergent tectonic boundaries were expanding the Tethys Ocean during the Paleozoic Era (541-252 million years ago). This is the oldest seafloor that still lies beneath the ocean waters, all the older seafloor around the world has already been recycled into the deep Earth by subduction. As these last vestiges of Paleozoic Era oceanic seafloor are subducted beneath Europe, it is causing volcanos in Italy and Greece to erupt, the Alps to uplift, and the Greek Islands to rise out of the waters.

Corfu Triassic Period marine rocks
Triassic Period Tethys seafloor rocks uplifted to form the Island of Corfu in Greece

Only a few million years ago the Tethys Sea met its end when it was cut off from the Atlantic Ocean during the Messinian Salinity Crisis 5.96-5.33 million years ago. As Africa and Europe converged tectonically, the western channel between the Atlantic and the Tethys was squeezed closed. The Tethys waters evaporated away, leaving behind layers of salt up to 3 kilometers thick. Tens of thousands of years later, when the land bridge that had separated the Atlantic from the Tethys was broken, the Mediterranean Sea was filled by the catastrophic Zanclean flood. The Mediterranean Sea formed in place of its once great predecessor. For now the Mediterranean Sea is the 10th largest body of water on Earth, until it too is lost to tectonics and time.

In time, the Mediterranean, Black, Caspian, & Aral Seas will all dry up as the land that was once a great ocean is uplifted by the ongoing tectonic collision. When the Mediterranean Sea is completely closed, Africa and Europe will be one large continent and the waters that cover the last remnants of the Tethys oceanic floor will drain and evaporate away. The Tethys is not the first great ocean to close up and it will not be the last.


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