In Israel - on every tour, every guide will always tell you: "There used to be a sea here."
- Nir Topper
- Jun 10
- 4 min read
The Tethys Ocean was a vast, ancient ocean that spanned across the Earth's ancient continents for hundreds of millions of years. Its name is derived from Greek mythology, where Tethys was one of the Titans—an ancient and powerful race of gods who ruled the world before the Olympian gods (such as Zeus). Tethys herself was the Titan goddess of the primal font of fresh water, the sister and wife of Oceanus, and the mother of the numerous river and spring gods. The choice of this name hints at the size and power of this ancient ocean, but for the land of Israel, its significance goes much deeper than a mythological name; it is the principal architect of the landscape we see around us. To understand the geology of Israel, our mountains, valleys, and even our natural resources, we must familiarize ourselves with the history of the Tethys Ocean.
The geological history of the Land of Israel is characterized by a prolonged struggle between sea and land. Before the appearance of the Tethys Ocean—over 540 million years ago—the region was part of the supercontinent "Gondwana." During this period, hard, magmatic, and metamorphic rock (igneous rocks) was formed, which is currently exposed primarily in the Eilat and southern Sinai region, giving it its reddish-pink hues.
After a long period of weathering of those continental igneous rocks, the region began to subside, until about 250 million years ago, the waters of the Tethys Ocean gradually began to flood the area that would later become the Land of Israel. This process occurred in waves—with repeated rises and falls in sea level. For the next tens of millions of years, the Land of Israel was mostly covered by a relatively shallow sea—until about 66 million years ago.
This shallow, warm sea teemed with life: algae, oysters, snails, sea urchins, and ammonites—extinct cephalopods, relatives of modern octopuses and squids, possessing a spiral shell. When these creatures died, their skeletons and shells—primarily composed of calcium carbonate—sank to the seabed. Over millions of years, through a process of accumulation and pressure, these sediments became marine sedimentary rocks. This is the source of the limestone, chalk, and dolomite rocks that make up the vast majority of the bedrock in Israel. The Jerusalem hills, the Galilee, the Carmel, and Judea and Samaria—are all built from those same marine sedimentary rocks that formed on the floor of the Tethys Ocean. The numerous fossils that can be found in these rocks—ranging from tiny snails to shark teeth and even the remains of marine reptiles—are tangible and fascinating evidence of that rich marine past.
But the sea did not remain here forever. Already about 100 million years ago, the African continent began to move slowly northwards towards the Eurasian continent. This pressure caused the folding of the immense rock layers that had formed on the Tethys seabed—a process called "folding." This folding, known in geology as the "Syrian Arc," pushed the seabed upwards, creating the folds and ridges of the Land of Israel: the mountains and ridges in the Negev, the Judean and Samarian hills, the Carmel, and the ridges of the Lower and Upper Galilee. Concurrently, the Tethys Ocean gradually retreated from the area, until it completely closed off about 50 million years ago.
The retreat process was not uniform. There were periods when the sea returned and flooded certain areas, but the general trend was one of continental uplift. The present-day Mediterranean Sea is, in fact, the largest and most well-known remnant of that ancient Tethys Ocean. Other remnants of it include the Black Sea and the Caspian Sea—bodies of water that became isolated from Tethys as its northern branches closed.
Understanding the role of the Tethys Ocean is not merely a matter of distant history, but a critical tool for understanding the Land of Israel today. The limestone and chalk rocks, its products, shape the karstic landscape (caves, sinkholes), influence the types of soil that develop upon them (such as the fertile Terra Rossa soil), and constitute the main aquifers (the Mountain Aquifer) that store the country's groundwater. Even the natural gas reservoirs off the coast of Israel are connected to the geological legacy of the Tethys Ocean. Thus, an ocean that vanished tens of millions of years ago continues to shape and sustain the Land of Israel to this day.
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Image 1 - Map of the continents Laurasia and Gondwana during the Triassic period, 200 million years ago. Source: By Lennart Kudling - This image has been extracted from another file, CC BY 3.0
Image 2 - "The Ammonite Wall," Makhtesh Ramon. A unique limestone outcrop containing hundreds of fossils of ammonites—ancient marine creatures that lived in the area about 90 million years ago when the Negev was covered by a sea. Photo: Nir Toper. (Enlarge the image to see the fossilized ammonites).
Image 3 - Understanding the stages of landscape development in the Land of Israel through the story of the Tethys Ocean. Source: Nir Toper, via Google NotebookLM.
Image 4 - Remnants of the Tethys Ocean today - the Mediterranean, Caspian, and Black Seas. Source: Google Earth.
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