Earth's Layers and Tectonic Plates

A Slice of Earth

  • If we were to slice Earth like a cake, we would notice it has multiple layers.

  • The layers of Earth are:

    • Crust

    • Mantle

    • Core (which includes Outer Core and Inner Core)

The Crust

  • The Crust is the Earth’s topmost layer.

  • It is the thinnest layer.

  • It is primarily composed of rock and soil.

  • The crust is divided into two parts:

    • Continental Crust

    • Oceanic Crust

The Continental Crust

  • The continental crust covers approximately 30% of Earth’s surface.

  • It is composed mostly of granite and can be anywhere from 30 to 50 kilometers thick.

  • It makes up all landmasses found on Earth.

The Oceanic Crust

  • The oceanic crust forms about 70% of the Earth’s surface and makes up the ocean floor.

  • It can be anywhere from 5 to 10 kilometers thick.

  • It is made up mostly of basalt and other denser materials.

  • The continental crust is continually recycled by the layer below it – the mantle.

Tectonic Plates

  • The lithosphere, which includes the crust and the upper mantle, is broken into large pieces that move on the mantle below the crust.

  • These large pieces are called tectonic plates.

  • Tectonic plates can move one of three ways:

    • Apart from each other

    • Toward each other

    • Past each other

  • Mountains, valleys, and earthquakes form along plate boundaries (where two tectonic plates interact).

Pangea and the Continental Drift

  • Continental Drift describes one of the earliest theories regarding how continents moved over time.

  • In the early 20th century, scientist Alfred Wegener believed that the continents were “drifting” across the Earth, sometimes plowing through oceans and into each other.

  • Wegener was convinced that all of Earth’s continents were once part of an enormous, single landmass called Pangea.

The Ring of Fire

  • The “Ring of Fire” is an area on Earth where tectonic plates meet.

  • These tectonic plates move around a lot, and the crust is thin and fractured here.

  • Most of Earth’s volcanoes and earthquakes happen on the “Ring of Fire”.

Types of Boundaries

  • There are three types of plate boundaries (where two tectonic plates meet). They are:

    • Convergent Boundaries

    • Divergent Boundaries

    • Transform Boundaries

Convergent Boundaries

  • The word converge means to come together.

  • So, convergent boundaries are when two plates collide, pushing against each other, and form mountains!

  • Convergent boundaries move towards each other.

Divergent Boundaries

  • The word diverge means to move away.

  • So, divergent boundaries are when two plates move apart from each other.

  • This mostly happens in oceanic regions, and forms new oceanic crust.

  • Divergent boundaries move away from each other. They form volcanoes!

Transform Boundaries

  • Transform boundaries form when two plates slide past each other, or move laterally each other.

  • When these two plates slide past each other, a large amount of stress is built up.

  • This often causes earthquakes.

The Mantle

  • The Mantle is Earth’s second layer.

  • The mantle is VERY hot and under great pressure.

  • The pressure that builds up in the mantle is what causes the tectonic plates on the crust to move.

  • It is made of solid and melted rock.

  • The mantle is approximately 2,900 kilometers thick.

The Core

  • The Core is the center of the Earth.

  • It is split into two parts:

    • Outer Core

    • Inner Core

  • The core is the hottest part of the Earth.

The Outer Core

  • The outer core is made of liquid iron and nickel.

  • The convection in the outer core is responsible for Earth's magnetic field.

  • As Earth spins on its axis, the liquid inside the outer core carries around.

The Inner Core

  • The inner core is under so much pressure that it is made of solid iron.

  • The temperature of the inner core is approximately 4,000 to 6,000 degrees Celsius – that's up to 6,000 times hotter than our human bodies and scorching enough to make metal melt!

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