SSC
The hypothesis of sea-floor spreading was put forward in 1962 by the American geologist:
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Answer: Option A — Harry Hammond Hess
Detailed Solution
In 1962, the American geologist and US Navy officer Harry Hess published his idea of sea-floor spreading in a paper titled "History of Ocean Basins".
Main ideas of sea-floor spreading:
- New oceanic crust is formed at mid-ocean ridges, long underwater mountain chains running through the oceans.
- Hot molten rock (magma) rises from the mantle at the ridges, cools and forms new sea floor.
- This new crust moves away on both sides of the ridge, like two conveyor belts.
- The oldest oceanic crust is destroyed when it sinks back into the mantle at deep ocean trenches.
- So, the ocean floor is constantly being renewed, and the continents are carried along as the sea floor moves.
Background:
- During the Second World War, Hess commanded a US Navy ship and used its echo sounder (sonar) to map the ocean floor.
- Studies of the ocean floor revealed long ridges, deep trenches and flat-topped underwater mountains called guyots.
Evidence supporting sea-floor spreading:
Magnetic striping: Rocks on either side of mid-ocean ridges show matching stripes of normal and reversed magnetism, recording reversals of the Earth's magnetic field as new crust formed. This was explained by Vine, Matthews and Morley in 1963.
Age of rocks: The ocean floor is youngest at the ridges and becomes older farther away. No oceanic crust is older than about 180 to 200 million years, while continental rocks can be about 4 billion years old.
Thin sediments: Sediments on the ocean floor are thin near the ridges and thicker away from them.
Importance:
- Sea-floor spreading explained how continents could move, giving strong support to the earlier idea of continental drift.
- It became one of the main building blocks of the theory of plate tectonics, developed later in the 1960s.
Why not the other options?
- ✗Arthur Holmes proposed the convection current theory in the 1930s.
- ✗Charles Lyell popularised uniformitarianism in the 19th century.
- ✗Charles Darwin proposed the theory of evolution by natural selection.
Quick tip
Remember: Sea-floor spreading = Harry Hess (1962, "History of Ocean Basins"); evidence from magnetic stripes and young crust at ridges.
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Oceans & Hydrosphere — Preparation
This question tests your understanding of Oceans & Hydrosphere, a key topic in the General Knowledge section. The detailed solution above uses a step-by-step approach to show the reasoning, and where available, a shortcut that helps you solve similar questions in under 90 seconds during the actual exam.
This topic covers the hydrosphere: the oceans and seas of the world, ocean relief features such as trenches and ridges, ocean currents, tides, waves, salinity, and the world's major lakes, straits, gulfs and islands. Questions commonly ask about the largest and deepest ocean (the Pacific, with the Mariana Trench), warm and cold ocean currents, the causes of tides, and which water bodies a strait connects. For example, the Palk Strait separates India and Sri Lanka, and the Strait of Gibraltar connects the Atlantic Ocean and the Mediterranean Sea. Practise the oceans and hydrosphere questions below, written in the style of the general awareness sections of exams such as SSC, banking, railways, CUET GAT, MAH CET and CLAT. Each question comes with a detailed explanation that adds related facts, so every question helps you revise more than one point.