Distribution of seas and oceans Test - 1

Most volcanic activity on the seafloor takes place on mid-ocean ridges.

These facts and a detailed analysis of the magnetic properties of the rocks on either side of the mid-oceanic ridge led Hess (1961) to propose his hypothesis, known as the “sea floor spreading”. Hess argued that constant eruptions at the crest of oceanic ridges cause the rupture of the oceanic crust and the new lava wedges into it, pushing the oceanic crust on either side. 

The earliest marine deposits along the coastline of South America and Africa are of the Jurassic age.

However, it was Alfred Wegener, a German meteorologist who put forth a comprehensive argument in the form of  “the continental drift theory” in 1912.

Pangaea first broke into two large continental masses as Laurasia and Gondwanaland forming the northern and southern components respectively.

A tectonic plate (also called lithospheric plate) is a massive, irregularly shaped slab of solid rock, generally composed of both continental and oceanic lithosphere. Plates move horizontally over the asthenosphere as rigid units. The lithosphere includes the crust and top mantle with its thickness range varying between 5 and 100 km in oceanic parts and about 200 km in the continental areas.

Wegener had thought of all the continents to have initially existed as a supercontinent in the form of Pangaea.

 The rate at which seawater cycles through these systems is influenced by several factors, but on average, it is estimated that the entire volume of the oceans cycles through submarine hydrothermal systems roughly every 10 million years.

Some important minor plates are listed below: (i) Cocos plate: Between Central America and Pacific plate (ii) Nazca plate: Between South America and Pacific plate (iii) Arabian plate: Mostly the Saudi Arabian landmass (iv) Philippine plate: Between the Asiatic and Pacific plate (v) Caroline plate: Between the Philippine and Indian plate (North of New Guinea) (vi) Fuji plate: North-east of Australia.

The earth is considered to have 15 major tectonic plates. Seven of which are primary plates and the rest are secondary plates. The primary plates are the African plate, the Antarctic plate, the Eurasian plate, the Indo-Australian plate, the North American plate, the Pacific plate, and the South American plate.