Question

define the term earths plates

Answer 1

these plates are located below the earth curst . They in large number . Inbalance of these plates cause earthquake .

Answer 2

What Is the Definition of a Tectonic Plate?

To define tectonic plates, it's best to start with a description of the Earth’s components. The Earth has three layers: The crust, the mantle and the core. The crust is the Earth’s surface, where people live. This is the hard surface you walk on every day. It is a thin layer, thinner under the ocean and thicker in spots where there are mountain ranges, like the Himalayas. The crust serves as insulation for the center of the Earth. Just underneath the crust, the mantle is solid. The solid part of the mantle combined with the crust make up what is called the lithosphere, which is rocky. But the further down into the Earth you go, the mantle becomes molten and has very hot rock that can mold and stretch without breaking. That part of the mantle is called the asthenosphere.

The best way to define tectonic plates is that they are parts of the lithosphere that break up into huge rock slabs, or crustal plates. There are a few really large plates and several smaller plates. Some of the major plates include the African, Antarctic and North American plates. Tectonic plates basically float on the asthenosphere, or molten mantle. While it is strange to think about, you are in fact floating on these slabs called tectonic plates. And under the mantle, the Earth’s core is very dense. Its outer layer is liquid and the inner layer of the core is solid. This core consists of iron and nickel, and it is extremely hard and dense.

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The first person to theorize that tectonic plates existed was German geophysicist Alfred Wegener, in 1912. He noticed that the shapes of western Africa and eastern South America looked as though they could fit together like a puzzle. Displaying a globe that shows these two continents and how they fit is a great way to demonstrate plate tectonics for kids. Wegener thought that the continents must once have been joined together, and somehow moved apart over many millions of years. He named this supercontinent Pangaea, and he called the idea of the continents moving “continental drift.” Wegener went on to discover that paleontologists had found matching fossil records in both South America and Africa. This bolstered his theory. Other fossils were found matching up the coasts of Madagascar and India, as well as Europe and North America. The kinds of plants and animals found could not have traveled across huge oceans. Some fossil examples include a land reptile, Cynognathus, in South Africa and South America, as well as a plant, Glossopteris, in Antarctica, India and Australia.

Another clue was evidence of ancient glaciers in the rocks in India, Africa, Australia and South America. In fact, scientists called paleoclimatologists now know these striated rocks proved that glaciers existed over those continents roughly 300 million years ago. North America, in contrast, was not covered in glaciers at that time. Wegener could not, with his technology at the time, explain fully how continental drift worked. Later, in 1929, Arthur Holmes suggested that the mantle underwent thermal convection. If you have ever seen a pot of water boil, you can see what convection looks like: heat causes the hot liquid to rise to the surface. Once at the surface, the liquid spreads, cools, and sinks back down. This is a good visualization of plate tectonics for kids and shows how convection of the mantle works. Holmes thought that thermal convection in the mantle caused heating and cooling patterns that could give rise to continents, and in turn break them down again.

Decades later, research of the ocean floor revealed oceanic ridges, geomagnetic anomalies, massive ocean trenches, faults and island arcs that seemed to support Holmes’ ideas. Harry Hess and Robert Deitz then theorized that sea floor spreading was occurring, an extension of what Holmes had guessed. Sea floor spreading meant that the ocean floors spread out from the center and sank at the edges, and were regenerated. Dutch geodesist Felix Vening Meinesz found something quite interesting about the ocean: The Earth’s gravitational field was not as strong in the deepest parts of the sea. He therefore described this area of low density as being pulled down to the mantle by convection currents. The radioactivity in the mantle causes the heat that leads to the convection, and therefore the plate movement.