Meaning of Plate Tectonics
The term “plate” was coined by Canadian geophysicist J.T. Wilson in 1965 to refer to a solid landmass on Earth. The study of the nature and movement of these plates is known as plate tectonics. The concept of plates emerged from two observations:
(1) The movement of continents and (2) The expansion of the ocean floor.
Morgan identified six major and fourteen minor plates worldwide. These plates can move independently, and their edges are of particular interest because earthquakes, volcanoes, and other tectonic activity occur along them. Thus, studying these edges is crucial. Plate edges can be broadly categorized into three types:
(1) Destructive plate edge – where materials move downward, and the plate edges wear out. (2) Conservative plate edge – where two plates move side by side, creating friction, but without a difference in surface area. (3) Constructive plate edge – where new materials are formed, such as the Mediterranean Ridge.
Harry Hess’s Plate Tectonics Theory
In 1960, Harry Hess proposed the plate tectonic theory to explain the movement of continents. Hess suggested that continents and oceans rest on different plates. As these plates move, they also displace the continents and ocean floors. From the Carboniferous era, the current continents and oceans have been formed due to the transfer and flow of various plates of Pangea. The formation of landmasses may continue to change in the future as plate movements are ongoing.
Related-
- Describe the Concept of Normal Erosion Cycle Propounded by Davis.
- How were the oceans and continents formed? Discuss the Quaternary Theory.
- Discuss the Tidal Hypothesis of the Origin of the Earth.
The edges of a tectonic plate can be classified into three categories:
- The center where two plates move in opposite directions is called the creep center. New material is created here, making the edges constructive.
- The edges where two plates collide are called destructive edges because the edge of one plate, made of heavy material, sinks into the earth’s mantle and is destroyed.
- The edges where two plates slide side-by-side and have no interaction are called protective edges. The process of mountain formation becomes complicated at these edges. It is important to note that plates can be oceanic or terrestrial.
There are six major plates: Eurasian, Indian, American (also known as North America or Laurentia), African, Antarctic, and Pacific Ocean plates.
The origin of fold mountains can be explained by plate tectonics theory. Mountains can form when a continental and oceanic plate collide, when two continental plates collide, or when two plates with an oceanic bottom crust collide. The Rocky and Andes ranges were formed due to the collision of the Pacific Ocean Plate and the American Plate. The Himalayas were formed when the Asian and Indian plates collided. The island arc of Japan is an example of the formation of mountains due to the collision of plates with an oceanic bottom crust.
Before the Cambrian era, the continental parts were smaller than they are now. The size of continents increased due to the formation of island arcs and their collision with continental coastal parts. The Atlantic Ocean has been expanding while the Pacific Ocean has been contracting due to the movement of the American Plate