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Tectonic Plates

The Earth, in a nutshell

Table of Contents

The Earth in a nutshell

Earth is made up of tectonic plates; plates of crust that float on the mantle. Here’s a table of the different parts of the Earth.

Part of the Earth Description
Crust Thin and rocky
Mantle Semi-molten rock
Outer Core Liquid nickel and iron
Inner Core Solid nickel and iron

Sometimes we refer to them in regions.

Part of the Earth Description
Lithosphere Made up of crust and upper mantle
Aesthenosphere Below the lithosphere

Earth’s crust is a thin and rocky section of the Earth that is about 8km thick. It floats on top of semi-molten rock in the mantle, which in turn floats on nickel and iron.

Wegener’s Theory of Continental Drift

Alfred Wegener theorised that the Earth’s crust was made up of plates that were floating on denser magma. This was called the theory of continental drift. Today, the theory of tectonic plates succeeds continental drift theory. He also theorised that the continents of the world used to be one gigantic supercontinent, which he named Pangea. There were a number of different supercontinents as land broke away and joined together repeatedly.


Evidence for the theory of continental drift

Evidence for this includes:

  1. The east coast of South America and the west coast of South America match up together Earth is a jigsaw puzzle!
  2. There are similar patterns for rocks on different continents (e.g the Appalachian Mountains in North America seem to continue into the Caledonian Mountains in Scandinavia) MOUNTAINS!!!
  3. Similar fossils have been found on different continents, for example, fossils of the Mesosaurus have been found in both in both South Africa and Brazil. Cold areas such as Greenland have tropical fossils, and South Africa has ice scratches on rocks despite it’s warm climate. Fossils and stuff
  4. There are coal deposits in cold parts of the world (such as Antarctica) and glacial deposits in hot parts of the world (such as South Africa, Australia, South America and India) which seems to suggest that these landmasses were once joined together. Glacial deposits around the world
  5. Tectonic and seismic activity seems to concentrate on the boundaries of the plates, known as the Ring of Fire. Global Earthquakes
  6. The magnetic north pole continually moved around1

Tectonic activity is the reason that our natural terrain is extremely varied. The Mid-Ocean Ridge and Marianas Trench are some examples of terrain formed by a divergent boundary and a convergent boundary respectively. The San Andreas Fault in California is a good example of a transform boundary.

Moooooove over!

How do plates move?

Plates move in three primary ways2.

  1. Divergent Boundaries

    Divergent boundaries are when two plates separate and move away from each other. Divergent boundary

  2. Convergent Boundaries

    Convergent boundaries are when two plates move towards each other, forcing one plate to dive beneath the other. This process is known as subduction. Convergent boundary

  3. Transform Boundaries

    Transform boundaries are when two plates slide past each other, causing a fault. A good example of a transform boundary is the San Andreas Fault in California, United States. Transform boundary

Why do plates move?

Plates move because of convection currents in the molten liquid rock in the mantle.

Convection currents in the asthenosphere

Heat generated from the really hot outer core rises, and when it gets to the top, is blocked by the crust, spreads out at the top, and falls when it begins to cool. This moves the boundaries of the plates. As a result, the crust is affected by changing boundaries and this is what causes magma to upwell, usually at the site of divergent boundary (volcanic activity).

History of Tectonic Plates1

Alfred Wegener proposed the theory of continental drift, and that continents “plower This was due to the geographical evidence where coastlines fit together. Paleontologists – fossil scientists, found fossils on different continents. Moving into the present, underwater seisometers meant to alert nuclear activity showed that there was increased volcanic and seismic activity around the edges of plates. This, which occurred in the 1960s, basically made plate tectonic theory the dominant accepted theory for how the Earth was shaped.

Folds, Faults and Subduction


  • Earth’s crust bends, and this causes folding
  • When plates collide and are forced into each other, folding occurs. This process is known as compression.
  • Horizontal compression occurs which creates mountains.
  • This process occurs at collision zones.


In folding mountains, the part folded upwards is the anticline and the part folded downwards is the syncline.

Anticline and Syncline

Age of anticline and Syncline

More on Fold Mountains on BBC Bitesize GCSE Geography


  • Tectonic plates horizontally slip
  • This process is known as rifting, where the lithosphere is torn apart

In fault-block mountains, the raised block is the horst while the lowered block is the graben.

Fault mountain


Destructive Plate Margins on BBC Bitesize

  • A geological process at convergent boundaries, where one plate dives under another
  • Most common with an oceanic plate, and a continental plate
  • The oceanic plate is denser, and it moves below the continental plate
  • This triggers earthquakes
  • This process occurs at the subduction zone.

Subduction zone

When subduction occurs, it usually means that crust will be subducted too. This means that mantle from the asthenosphere will be upwelled to form new crust.

Seafloor upwelling/spreading


Seismic and volcanic activity are more likely at the boundaries of tectonic plates. Most of the sliding, pushing, pulling, seafloor spreading and upwelling occurs along the tectonic plates. A large number of earthquakes and volcanic activity occur around the Pacific Plate. This is known as the Ring of Fire.

Ring of Fire

We can measure how much energy an earthquake produces using the Richter scale, which is a scale of magnitude. Every increase of 1 on the scale is an increase of amplitude by 10. Familiarise yourself with the Richter scale now.

Magnitude Description Mercalli intensity Average earthquake effects Average frequency of occurrence globally (estimated)
1.0–1.9 Micro I Microearthquakes, not felt, or felt rarely. Recorded by seismographs.[30] Continual/several million per year
2.0–2.9 Minor I to II Felt slightly by some people. No damage to buildings. Over one million per year
3.0–3.9   III to IV Often felt by people, but very rarely causes damage. Shaking of indoor objects can be noticeable. Over 100,000 per year
4.0–4.9 Light IV to VI Noticeable shaking of indoor objects and rattling noises. Felt by most people in the affected area. Slightly felt outside. Generally causes none to minimal damage. Moderate to significant damage very unlikely. Some objects may fall off shelves or be knocked over. 10,000 to 15,000 per year
5.0–5.9 Moderate VI to VII Can cause damage of varying severity to poorly constructed buildings. At most, none to slight damage to all other buildings. Felt by everyone. 1,000 to 1,500 per year
6.0–6.9 Strong VIII to X Damage to a moderate number of well-built structures in populated areas.Earthquake-resistant structuressurvive with slight to moderate damage. Poorly designed structures receive moderate to severe damage. Felt in wider areas; up to hundreds of miles/kilometers from the epicenter. Strong to violent shaking in epicentral area. 100 to 150 per year
7.0–7.9 Major X or greater Causes damage to most buildings, some to partially or completely collapse or receive severe damage. Well-designed structures are likely to receive damage. Felt across great distances with major damage mostly limited to 250 km from epicenter. 10 to 20 per year
8.0–8.9 Great   Major damage to buildings, structures likely to be destroyed. Will cause moderate to heavy damage to sturdy or earthquake-resistant buildings. Damaging in large areas. Felt in extremely large regions. One per year
9.0 and greater     At or near total destruction – severe damage or collapse to all buildings. Heavy damage and shaking extends to distant locations. Permanent changes in ground topography. One per 10 to 50 years


Many earthquakes occur underwater. When earthquakes occur, they can trigger waves. Waves travel long distances, and as the water gets shallower, the waves slow down. Then, they become higher and more closely packed. Adrian personally suggests you to check Tsunamis on BBC Bitesize for a better understanding!

Tsunamis on BBC Bitesize GCSE Edexcel


Lava and Magma

NOTE: Volcanoes will remain somewhat because it isn’t being covered at Adrian’s school. If you’d like to contribute, feel free to. Otherwise, please check out BBC Bitesize’s information on volcanoes

Lava and Magma

Volcanoes are formed when magma escapes through cracks in the crust and spews out as lava.

Magma is molten rock. Then, when it escapes, it cools down and hardens as lava.


Australia lies in the centre of the Australian plate, which keeps it relatively immune from seismic and volcanic activity. As the mainland is not near any plate boundaries it doesn’t occur near Australia a lot. This makes Australia quite a stable continent.

Footnotes and Other Notes

Copyright © 2017-2020 aidswidjaja and other contributors. CC BY-SA 4.0 Australia unless otherwise stated.