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https://www.nationalgeographic.org/media/plate-tectonics/
This video from national geographic can help further explain the theory of tectonic plates.

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Photograph by Georg Gerster

Plate tectonics is a scientific theory that explains how major landforms are created as a result of Earth's subterranean movements. The theory, which solidified in the 1960s, transformed the earth sciences by explaining many phenomena, including mountain building events, volcanoes, and earthquakes.

In plate tectonics, Earth's outermost layer, or lithosphere-made up of the crust and upper mantle-is broken into large rocky plates. These plates lie on top of a partially molten layer of rock called the asthenosphere. Due to the convection of the asthenosphere and lithosphere, the plates move relative to each other at different rates, from two to 15 centimeters (one to six inches) per year. This interaction of tectonic plates is responsible for many different geological formations such as the Himalaya mountain range in Asia, the East African Rift, and the San Andreas Fault in California, United States.

The idea that continents moved over time had been proposed before the 20th century. However, a German scientist named Alfred Wegener changed the scientific debate. Wegener published two articles about a concept called continental drift in 1912. He suggested that 200 million years ago, a supercontinent he called Pangaea began to break into pieces, its parts moving away from one another. The continents we see today are fragments of that supercontinent. To support his theory, Wegener pointed to matching rock formations and similar fossils in Brazil and West Africa. In addition, South America and Africa looked like they could fit together like puzzle pieces.

Despite being dismissed at first, the theory gained steam in the 1950s and 1960s as new data began to support the idea of continental drift. Maps of the ocean floor showed a massive undersea mountain range that almost circled the entire Earth. An American geologist named Harry Hess proposed that these ridges were the result of molten rock rising from the asthenosphere. As it came to the surface, the rock cooled, making new crust and spreading the seafloor away from the ridge in a conveyer-belt motion. Millions of years later, the crust would disappear into ocean trenches at places called subduction zones and cycle back into Earth. Magnetic data from the ocean floor and the relatively young age of oceanic crust supported Hess's hypothesis of seafloor spreading.

There was one nagging question with the plate tectonics theory: Most volcanoes are found above subduction zones, but some form far away from these plate boundaries. How could this be explained? This question was finally answered in 1963 by a Canadian geologist, John Tuzo Wilson. He proposed that volcanic island chains, like the Hawaiian Islands, are created by fixed "hot spots" in the mantle. At those places, magma forces its way upward through the moving plate of the sea floor. As the plate moves over the hot spot, one volcanic island after another is formed. Wilson's explanation gave further support to plate tectonics. Today, the theory is almost universally accepted.

Director

Tyson Brown, National Geographic Society

Author

National Geographic Society

Production Managers

Gina Borgia, National Geographic Society

Jeanna Sullivan, National Geographic Society

Program Specialists

Sarah Appleton, National Geographic Society, National Geographic Society

Margot Willis, National Geographic Society

Last Updated

August 17, 2022

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The theory of plate tectonics revolutionized the earth sciences by explaining how the movement of geologic plates causes mountain building, volcanoes, and earthquakes.

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Seismic waves are measured by a device called a seismograph. Seismographs detects ground motion and records a signal. The information taken from seismographs are used to determine the strength and location of the earthquake.
Magnitude: Magnitudes are numbers that represent the strength of an earthquake, and it uses the Richter scale.

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Lithosphere: The Earth’s lithosphere is composed of crust and parts of the upper mantle, and consists of tectonic plates.
Asthenosphere: Tectonic plates move and float slowly on the Asthenosphere. The Asthenosphere is a layer that’s made up of extremely hot material. It enables the plates to move because the hot material can flow (like toothpaste)
References: 4.1 Notes

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Tectonic plates are huge slabs of rock (plates) that make up the Earth’s surface. Most tectonic plates are oceanic and continental crust, but some are ONLY oceanic crust.
References: 4.1 Notes

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Hot spots are hot, fixated regions of the Earth’s mantle where magma rises to the surface and break through the weak parts of the lithosphere. Tectonic plates move over those hot spots and form volcanoes from magma rising and melting through the crust.

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This is when an oceanic crust has collided with a continental crust. Volcanoes form on the surface of the continental crust and magma can rise to the surface, causing an eruption.

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This is when an oceanic crust collides with another oceanic crust. A denser plate subducts a less dense plate and an oceanic trench forms. Magma rises to the upper plate and some lava is released onto the surface. Overtime, erupted lava and ash build up and form volcanic islands.

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Volcanoes are an opening in the Earth’s surface where magma and other materials are released. Most volcanoes occur at convergent boundaries when oceanic crust collide with another plate.

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Mountain ranges can form when two plates of continental crust collide. Since continental crusts are not easily subducted, the impact can cause a large area to be pushed up, forming mountains.

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The release of energy from earthquakes can cause vibrations called seismic waves, and there are 3 types:
Primary Waves (P Waves):
These waves move the fastest and are usually the first ones detected in an earthquake. They can cause rock particles to move forward and backwards, and can travel through liquids and solids.
Secondary Waves (S Waves):
These waves move slower than P waves and cause rock particles to move up and down. However, they can only travel through solids.
Surface Waves (L Waves):
These waves are the slowest among the three waves but often cause the greatest damage. They can only travel along the surface of the Earth and cause rock particles to move up, down, and side to side.

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There are 3 different types of faults:
Reverse Fault: It forms when rocks are squeezed together and one block overlaps another block. and the crust is shortened horizontally.
Normal Fault: Normal faults form when rocks are pulled apart and one block slips downward, and the crust is lengthened.
Strike-Slip Fault:It forms when blocks of rock move past each other horizontally.

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The movements in the Earth's crust can squeeze, stretch, or twist, which applies pressure to the rock. When too much pressure is applied, a break in the crust (called a fault) occurs, and the stored energy is released as an earthquake.

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References: BC Science 8 Textbook and 4.3 notes

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Ridge push lifts the lithosphere and pushes tectonic plates apart at divergent plate boundaries. The old material gets pushed aside by new material, which pushes the plates apart, and rising material spreads out as it reaches the upper mantle.

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Slab pull happens at convergent boundaries. It's the pulling of a tectonic plate due to gravity and suduction. As the leading edge of the plate sunks, it pulls the rest of the plate with it, almost like a conveyer belt.

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Energy from radiocative decay of some elements in the Earth's interior and from the core, heat up parts of the mantle. Warmer, less dense material rises, and cooler, denser material, sinks. This causes very large convection currents within the mantle, called mantle convection. As the material moves, it drags the tectonic plates along with it. There are 2 important processes of mantle convection.

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Divergent Plate Boundaries: Tectonic plates move apart in these boundaries during sea-floor spreading. This process can also happen in the middle of contients, which is known as continental rifting.
Convergent Plate Boundaries:Tectonic plates collide in a proccess called subduction. Subduction is a proccess where a denser crust goes below a less dense crust and causes deep sea trenches, volcanoes, and mountains to form. Earthquakes also happen in these boundaries.
Transform Plate Boundaries: Tectonic Plates slide past each horizontally, and earthquakes are also common in these boundaries.

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Tectonic plates can move in different directions at different rates. When plates interact at their edges, they're called plate boundaries. There are three types of plate boundaries:

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References: BC Science 8 Textbook and 4.2 notes

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Crust: A thin layer of rock surrounding the Earth. The oceanic crust is thinner and mostly basalt while the continental crust is mostly granite.
Upper Mantle: The top part of the upper mantle is solid, but the bottom part is made of rock that is soft-like taffy and can flow.
Lower Mantle: It's denser and has more solid material than the upper mantle.
Outer Core: The only layer that is liquid.
Inner Core: It's the deepest and hottest layer and it's solid because of the extreme pressure it's under in.
References: 4.1 Notes

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Scientists study the energy waves during earthquakes to infer about the different layers of the Earth. The speed and behaviour of the waves are affected by the materials they pass through.
References: 4.1 Notes

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The proccess begins when there's a rift/crack at the center of the valley in the mid-ocean ridge and magma from inside the Earth rises to fill in the crack. Then the magma cools and hardens into new rock, pushing older rock away from the ridge. This led to the understanding of how continents can move because they can be carried by the ocean floor widening during sea-floor spreading. This also provided support to Alfred's continental drift theory.
Reference: Mr. Chong's 4.1 notes

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Geologist Harry Hess suggested that new ocean crust is being made at mid-ocean-ridges and plate tectonics are moving away from each other in a proccess called sea-floor spreading.
References: 4.1 Notes

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References: BC Science 8 Textbook and 4.1 Notes

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German scientist Alfred Wegner proposed a theory that all the continents on Earth were once connected millions of years ago and called it 'Pangea'. He found that the continents fit like a puzzle and even found evidence to support his claim
References: BC Science 8 Textbook and 4.1 Notes

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Identical plant and animal fossils were found on several different continents and some of those fossils were not supposed to be there because it wasn't possible for the animal/plant to live in that area.
He found glacial deposits in hot places where ice can't form, and also found that some mountain ranges matched up, indicating they were once together.
References: BC Science 8 Textbook and 4.1 Notes