Why does plate tectonics move

C onvection currents describe the rising, spread, and sinking of gas, liquid, or molten material caused by the application of heat. An example of convection current is shown in Fig. Inside a beaker, hot water rises at the point where heat is applied. The hot water moves to the surface, then spreads out and cools. Cooler water sinks to the bottom. Magma is the molten rock below the crust, in the mantle. Tremendous heat and pressure within the earth cause the hot magma to flow in convection currents.

Based on evidence that has been found at plate boundaries, make some hypotheses about the movement of those plates. The earth has changed in many ways since it first formed 4. They have gradually moved over the course of hundreds of millions of years—alternately combining into supercontinents and pulling apart in a process known as continental drift.

The supercontinent of Pangaea formed as the landmasses gradually combined roughly between and mya. It is widely accepted by scientists today. Earthquakes and volcanoes are the short-term results of this tectonic movement.

The long-term result of plate tectonics is the movement of entire continents over millions of years Fig. The presence of the same type of fossils on continents that are now widely separated is evidence that continents have moved over geological history. Evaluate and interpret several lines of evidence for continental drift over geological time scales. The shapes of the continents provide clues about the past movement of the continents. The edges of the continents on the map seem to fit together like a jigsaw puzzle.

For example, on the west coast of Africa, there is an indentation into which the bulge along the east coast of South America fits.

The shapes of the continental shelves—the submerged landmass around continents—shows that the fit between continents is even more striking Fig. Some fossils provide evidence that continents were once located nearer to one another than they are today. Fossils of a marine reptile called Mesosaurus Fig. Another example is the fossil plant called Glossopteris, which is found in India, Australia, and Antarctica Fig.

The presence of identical fossils in continents that are now widely separated is one of the main pieces of evidence that led to the initial idea that the continents had moved over geological history.

Evidence for continental drift is also found in the types of rocks on continents. There are belts of rock in Africa and South America that match when the ends of the continents are joined.

Mountains of comparable age and structure are found in the northeastern part of North America Appalachian Mountains and across the British Isles into Norway Caledonian Mountains. These landmasses can be reassembled so that the mountains form a continuous chain. Evidence from glacial striations in rocks, the deep grooves in the land left by the movement of glaciers, shows that mya there were large sheets of ice covering parts of South America, Africa, India, and Australia.

These striations indicate that the direction of glacial movement in Africa was toward the Atlantic ocean basin and in South America was from the Atlantic ocean basin. This evidence suggests that South America and Africa were once connected, and that glaciers moved across Africa and South America.

There is no glacial evidence for continental movement in North America, because there was no ice covering the continent million years ago. North America may have been nearer the equator where warm temperatures prevented ice sheet formation. Mid-ocean ridges or spreading centers are fault lines where two tectonic plates are moving away from each other. Mid-ocean ridges are the largest continuous geological features on Earth.

They are tens of thousands of kilometers long, running through and connecting most of the ocean basins. Oceanographic data reveal that seafloor spreading is slowly widening the Atlantic ocean basin, the Red Sea, and the Gulf of California Fig.

The gradual process of seafloor spreading slowly pushes tectonic plates apart while generating new rock from cooled magma. Ocean floor rocks close to a mid-ocean ridge are not only younger than distant rocks, they also display consistent bands of magnetism based on their age Fig. NOV 15, NOV 16, NOV 17, Upcoming Virtual Events. DEC 01, DEC 07, JAN 25, FEB 23, MAR 10, Cancer Sucks T-Shirt.

Men's Women's. Opens in a new window Opens an external site Opens an external site in a new window. The Earth is dynamic thanks to its internal heat, which comes from deep within the mantle from the breakdown of radioactive isotopes. However, this theory is now largely out of favour, with modern imaging techniques unable to identify mantle convection cells that are sufficiently large to drive plate movement. Indeed, it is now accepted that plates and the mantle are a coupled system with plates moving by a process known as ' slab pull ' which helps to drive mantle convection patterns rather than the other way around.

Newly formed oceanic lithosphere at mid ocean ridges is less dense than the asthenosphere, but becomes denser with age as it cools and thickens. This causes it to sink into the mantle at subduction zones, pulling slabs of lithosphere apart at divergent boundaries and resulting in sea floor spreading or rifting.