At the beginning of the Mesozoic Era, a single great ocean covered most of the world. Known as the Panthalassa Ocean, this world sea surrounded the supercontinent Pangea. Centered on the equator and stretching from pole to pole, Pangea was shaped roughly like a large capital 'C' and within the cradle lay a separate body of water known as the Tethys Ocean.

During the Jurassic Period, shifting continents compressed the Tethys to form an equatorial seaway stretching from today's Caribbean Islands to what is now the Himalayas. Controlled by the restless tectonic energies of the planet, the shifting configurations of the Tethyan seas and seaways had profound impacts on the Earth's oceanic circulation and thus its climate.

For example, in Earth's present arrangement, extensive landmasses lie in the equatorial zone. This configuration prevents direct, continuous tropical circulation of ocean waters, which leads to the formation of closed-loop oceanic gyres that transfer heat energy from the equator to the poles. Large amounts of moisture are transferred to higher latitudes, which then supply plentiful-enough snowfall for glaciers and polar icecaps to develop: a planetary "icehouse" condition.

The opposite of the icehouse phase is the "greenhouse" condition, such as prevailed during much of the Mesozoic. The connected seas of the Tethys, Atlantic, and Pacific in the tropics allowed for equatorial waters to circulate freely in the Late Jurassic and Cretaceous, a system that sustains warmer global temperatures and discourages icecap formation.

The closure of the Tethys Sea was significant in obstructing this circum-equatorial flow. The development of the Isthmus of Panama, which joined North and South America and thus blocked the interchange of tropical Caribbean and Pacific waters.

This warm and relatively shallow seaway was a powerful transport current for the global circulation of floral and faunal elements. Whether the tropical effect of this ocean gateway played a role in the enormous size attained by dinosaurs is still uncertain, but it is an area of intense study.

Remnants of the Tethys remain in the Mediterranean, Caspian, Black, and Aral Seas. Ancient seafloor sediments help compose the lithified scaffold of the Alps, the Carpathians, the Pamirs, and other great Eurasian mountain ranges, and of course the Himalayas.

Traces of the ocean can also be found in stones called "shaligrams" or "saligrams", recovered from the Himalayas along the banks of the Gandaki River (Kali) in Nepal. The logarithmic spirals often found within these smooth stones are considered abstract representations of the divine in some traditions of Hinduism, Buddhism, and Jainism.