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Layers of the Earth/ Plate Tectonics Vocab

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The Earth's crust and upper part of the mantle [ mantle: A zone of hot rock in the interior of the Earth, located between the outer crust and the molten core. ] are broken into large pieces called tectonic plates. These are constantly moving at a few centimetres each year. Although this doesn't sound like very much, over millions of years the movement allows whole continents to shift thousands of kilometres apart. This process is called continental drift.

The plates move because of convection currents in the Earth's mantle. These are driven by the heat produced by the decay of radioactive elements and heat left over from the formation of the Earth.

Where tectonic plates meet, the Earth's crust becomes unstable as the plates push against each other, or ride under or over each other. Earthquakes and volcanic eruptions happen at the boundaries between plates, and the crust may 'crumple' to form mountain ranges.

Watch

You may wish to view this BBC News item from 2006 about the 100th anniversary of San Francisco's great earthquake.

It is difficult to predict exactly when an earthquake might happen and how bad it will be, even in places known for having earthquakes.

Alfred Wegener

The theory of plate tectonics and continental drift were proposed at the beginning of the last century by a German scientist, Alfred Wegener. Before his time it was believed that the planet's features, such as mountains, were caused by the crust shrinking as the Earth cooled after it was formed.

It took more than 50 years for Wegener's theory to be accepted. This was because it was difficult to work out what the mechanism was that could make whole continents move, and it was not until the 1960s that enough evidence was discovered to support the theory fully.

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The Earth's crust and upper part of the mantle [ mantle: A zone of hot rock in the interior of the Earth, located between the outer crust and the molten core. ] are broken into large pieces called tectonic plates. These are constantly moving at a few centimetres each year.

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Get access to files anywhere through secure cloud storage and file backup for your photos, videos, files and more with Google Drive.

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More info on Plate Tectonics

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Plate Tectonics: Further Evidence

This video segment adapted from A Science Odyssey uses animation and archival footage to provide an overview of the theory of plate tectonics. Early evidence showing striking similarities between regions on opposite sides of vast oceans suggested that in Earth's distant past what are now separate continents may once have been connected. However, this evidence said nothing about how the continents could have moved to their present positions.

This video is available in both English and Spanish audio, along with corresponding closed captions.

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This video segment adapted from A Science Odyssey uses animation and archival footage to provide an overview of the theory of plate tectonics. Early evidence showing striking similarities between regions on opposite sides of vast oceans suggested that in Earth's distant past what are now separate continents may once have been connected.

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Plate Tectonics, Earthquake and Volcanoes

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Plate Tectonics, Earthquake and Volcanoes

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Great interactive map!

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Plate Tectonics: An Introduction

In the early 1900s, most geologists thought that Earth's appearance, including the arrangement of the continents, had changed little since its formation. This video segment, adapted from the "Earth Explorer" episode of Discovering Women, describes the impact the theory of plate tectonics has had on our understanding of Earth's geological history, as we have become aware of our planet's ever-changing nature.

This video is available in both English and Spanish audio, along with corresponding closed captions.

# data[].attributes.attachment_link.description
In the early 1900s, most geologists thought that Earth's appearance, including the arrangement of the continents, had changed little since its formation. This video segment, adapted from the "Earth Explorer" episode of Discovering Women, describes the impact the theory of plate tectonics has had on our understanding of Earth's geological history, as we have become aware of our planet's ever-changing nature.

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Discover different types of plate boundaries.

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Divergent Boundary

A divergent (or spreading) boundary occurs where two plates move apart. Magma, or molten rock, rises from Earth's interior to fill the gap.

Earth's longest mountain range is an underwater chain 40,000 miles (65,000 km) long. It runs down the middle of the Atlantic Ocean (surfacing at Iceland), around Africa, through the Indian Ocean, between Australia and Antarctica, and north through the Pacific Ocean. Along the top of this ocean ridge is a deep crack, called a rift valley. Here, magma wells up from Earth's interior. Cooled by the sea, it solidifies into rock, creating new ocean floor.

In the North Atlantic ridge, 0.75 inches (2 cm) of new floor is created each year. In the East Pacific rise, the rate is 12.5 inches (32 cm) per year.

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A divergent (or spreading) boundary occurs where two plates move apart. Magma, or molten rock, rises from Earth's interior to fill the gap. Earth's longest mountain range is an underwater chain 40,000 miles (65,000 km) long. It runs down the middle of the Atlantic Ocean (surfacing at Iceland), around Africa, through the Indian Ocean, between Australia and Antarctica, and north through the Pacific Ocean.