The Indian subcontinent was once separated from the Asian mainland by a large ancient sea called the:

The Tethys Sea (or Tethys Ocean) was an ancient sea that lay between the northern supercontinent Laurasia and the southern supercontinent Gondwanaland. The Indian landmass, part of Gondwana, was separated from Asia by this sea.

Name:

It was named in 1893 by the Austrian geologist Eduard Suess, after Tethys, a sea goddess in Greek mythology.

Closing of the Tethys:

• As India broke away from Gondwana and moved rapidly northward, the floor of the Tethys Sea sank beneath the Asian plate, and the sea became narrower.
• About 50 million years ago, India collided with Asia, and the Tethys Sea between them closed.

Formation of the Himalayas:

• The thick layers of sediment that had collected on the floor of the Tethys Sea were squeezed, folded and lifted up between the two colliding landmasses.
• These folded sediments formed the Himalayas, the youngest and among the highest fold mountains in the world.
• That is why marine fossils, such as ammonites (called "Shaligram" in Nepal), are found high up in the Himalayas, even on the summit of Mount Everest, whose upper rocks are marine limestone.
• The Alps, the Carpathians and the Zagros Mountains were also formed from the closing of parts of the Tethys.

Remnants of the Tethys:

• The Mediterranean Sea, the Black Sea, the Caspian Sea and the Aral Sea are believed to be remnants of the ancient Tethys.
• The Northern Plains of India later formed when rivers filled the depression between the Himalayas and the Peninsular Plateau with sediment.

The Himalayas are still rising:

India continues to push northward into Asia at about 4 to 5 cm per year, so the Himalayas are still rising by a few millimetres each year, and earthquakes are frequent in the region.

Why not the other options?

• ✗The Rheic Ocean was an ancient ocean that closed when the supercontinent was assembled.
• ✗The Iapetus Ocean was an older ocean that closed long before, between North America and Europe.
• ✗The Sargasso Sea is a present-day sea in the North Atlantic.