Why do crustal plates move over time

One difference is that the mantle is not liquid; rather, the solid rocks are so hot that they can slowly flow. Hot, less dense rock material goes toward the crust whereas relatively denser, less hot material goes toward the core.

At certain times and places, hot, upflowing rock material in these convection cells weakens continental crust to create rifts and eventually new ocean basins. The East-African Rift, for instance, is the result of such a convection cell breaking up the African plate. Convection cells were responsible for the breaking up of supercontinents many times in Earth's history. Skip to main content.

Climate Sea Levels Why will sea level rise not be the same everywhere? How can we date corals? Geology and Tectonics Geology How do we know the age of the seafloor? Why is the seafloor so recent and the continental crust so old? Where do we find the oldest continental rocks and the oldest seafloor? What are the different types of rocks? What is a fossil and what are they used for?

What are hydrothermal vents, and why do we find them along mid-ocean ridges? Seismology What is a seismic wave? What is the difference between body waves and surface waves, and between P-waves and S-waves?

Why can't S-waves travel through liquids? It is composed of two distinctly different types of material: the less-dense continental crust and the more-dense oceanic crust. Both types of crust rest atop solid, upper mantle material. The upper mantle, in turn, floats on a denser layer of lower mantle that is much like thick molten tar. Each tectonic plate is free-floating and can move independently. Earthquakes and volcanoes are the direct result of the movement of tectonic plates at fault lines.

The term fault is used to describe the boundary between tectonic plates. Other observable results of short-term plate movement include the gradual widening of the Great Rift lakes in eastern Africa and the rising of the Himalayan Mountain range. The motion of plates can be described in four general patterns:. The rise of the Himalayan Mountain range is due to an ongoing collision of the Indian plate with the Eurasian plate.

Earthquakes in California are due to transform fault motion. 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.

If you have questions about how to cite anything on our website in your project or classroom presentation, please contact your teacher. They will best know the preferred format. When you reach out to them, you will need the page title, URL, and the date you accessed the resource. If a media asset is downloadable, a download button appears in the corner of the media viewer. If no button appears, you cannot download or save the media.

Text on this page is printable and can be used according to our Terms of Service. Any interactives on this page can only be played while you are visiting our website. You cannot download interactives. In , after decades of tediously collecting and mapping ocean sonar data, scientists began to see a fairly accurate picture of the seafloor emerge.

The Tharp-Heezen map illustrated the geological features that characterize the seafloor and became a crucial factor in the acceptance of the theories of plate tectonics and continental drift. Today, these theories serve as the foundation upon which we understand the geologic processes that shape the Earth. Join our community of educators and receive the latest information on National Geographic's resources for you and your students. Skip to content. Image San Andreas Fault Tectonic plate boundaries, like the San Andreas Fault pictured here, can be the sites of mountain-building events, volcanoes, or valley or rift creation.

This is known as slab pull. Recent research has shown that the major driving force for most plate movement is slab pull, because the plates with more of their edges being subducted are the faster-moving ones.

However, ridge push has also been presented in recent research to be a force that drives the movement of plates. If you've found the resources on this page useful please consider making a secure donation via PayPal to support the development of the site.

The site is self-funded and your support is really appreciated. If you've found the resources on this site useful please consider making a secure donation via PayPal to support the development of the site. Why do tectonic plates move? Why do plates move?