Today, these theories serve as the foundation upon which we understand the geologic processes that shape the Earth. Scientists look to these landforms and geologic events as evidence of plate tectonics, helping them both understand what happened in the past as well as predict what Earth will look like in the future.
The five activities in the Plate Tectonics module build a systems view of plate tectonics, engaging students in data exploration about plate boundaries and experimentation via computer-based models of plate motion. Join our community of educators and receive the latest information on National Geographic's resources for you and your students. Skip to content. Image by Naeblys.
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Related Resources. Plate Tectonics. View Collection. MapMaker: Tectonic Plate Boundaries. View Map. View Video. Plate Tectonics: What will Earth look like in million years? Where oceanic crust meets ocean crust Island arcs and oceanic trenches occur when both of the plates are made of oceanic crust. Zones of active seafloor spreading can also occur behind the island arc, known as back-arc basins.
These are often associated with submarine volcanoes. Where oceanic crust meets continental crust The denser oceanic plate is subducted, often forming a mountain range on the continent. The Andes is an example of this type of collision. Where continental crust meets continental crust Both continental crusts are too light to subduct so a continent-continent collision occurs, creating especially large mountain ranges. The most spectacular example of this is the Himalayas.
The space created can also fill with new crustal material sourced from molten magma that forms below. Divergent boundaries can form within continents but will eventually open up and become ocean basins. On land Divergent boundaries within continents initially produce rifts, which produce rift valleys. Under the sea The most active divergent plate boundaries are between oceanic plates and are often called mid-oceanic ridges.
The relative motion of the plates is horizontal. It wasn't until the mids that scientists began to study and measure earthquake activity in earnest, using a device developed in Italy called the seismograph [source: USGS , Shearer ].
Finally, in the mids, researchers in the United States and Great Britain came up with a theory that explained why the Earth shook [source: Silverstein]. The theory, called plate tectonics , is that the Earth's crust, or lithosphere , comprises many plates that slide over a lubricating asthenosphere layer.
At the boundaries between these huge plates of rock and soil, the plates sometimes move apart, and magma , or molten rock, comes to the surface, where it's called lava. It cools and forms new parts of the crust. The line where this happens is called a divergent plate boundary.
The plates also can push against each other. Sometimes, one of the plates will sink underneath the other into the hot layer of magma beneath it and partially melt. Other times, the edges of the two plates will push against each other and rise upward, forming mountains. This area is called a convergent plate boundary [source: Silverstein].
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