SSC
According to the theory of plate tectonics, the Earth's lithosphere is broken into:
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Answer: Option B — Seven major plates and several minor plates
Detailed Solution
The theory of plate tectonics states that the Earth's rigid outer shell, the lithosphere, is broken into large slabs called plates. There are seven major plates and a number of minor plates.
The seven major plates:
- Pacific Plate, the largest, lying mostly under the Pacific Ocean.
- North American Plate.
- South American Plate.
- Eurasian Plate.
- African Plate.
- Antarctic Plate.
Indo-Australian Plate. Many geologists now treat the Indian Plate and the Australian Plate separately.
Some minor plates:
Arabian Plate, Philippine Sea Plate, Caribbean Plate, Cocos Plate, Juan de Fuca Plate and Scotia Plate.
What the plates are made of:
- Each plate includes the crust and the uppermost part of the mantle.
- Plates may carry continents, ocean floor, or both.
- Plates range from about 100 km to 200 km in thickness.
How the plates move:
The plates move slowly, at about 1 to 10 cm per year, roughly the speed at which fingernails grow.
The movement is driven by heat from the Earth's interior. Slab pull, ridge push and mantle convection are the main forces.
What happens at plate edges:
- Most earthquakes, volcanoes and mountain-building take place along plate boundaries.
- Where plates move apart, new crust forms; where they move together, crust is destroyed or pushed up into mountains; where they slide past each other, faults such as the San Andreas Fault in California form.
The Indian Plate:
- The Indian Plate broke away from a southern landmass and moved north at a high speed.
- Its collision with the Eurasian Plate, which began about 50 million years ago, raised the Himalayas, which are still rising by a few millimetres a year.
Development of the theory:
The theory was developed in the 1960s, building on earlier ideas of continental drift and sea-floor spreading.
Why not the other options?
- ✗The lithosphere is not one continuous shell, nor divided into just two plates.
- ✗The plates are of very different sizes, not twelve equal parts.
Quick tip
Remember: Plate tectonics = 7 major plates (Pacific is the largest) + minor plates; plates move about 1 to 10 cm a year.
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Earth: Structure, Rocks & Landforms — Preparation
This question tests your understanding of Earth: Structure, Rocks & Landforms, 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 interior of the Earth (crust, mantle and core), types of rocks, plate tectonics and continental drift, earthquakes and volcanoes, and the landforms created by rivers, glaciers, wind and waves. Questions frequently ask about the layers of the Earth and their discontinuities, the three types of rocks (igneous, sedimentary and metamorphic), the Pacific 'Ring of Fire', and which agent forms which landform, such as river meanders and oxbow lakes or glacial cirques and moraines. Alfred Wegener proposed the continental drift theory in 1912. Practise the Earth's structure and landforms 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.