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## Major Landforms of the Earth ### Introduction The outermost layer of the Earth is a solid crust ranging in thickness from 5 km to 100 km. Below the crust is the mantle. The lithosphere includes the Earth's crust and the uppermost part of the mantle. Underlying the lithosphere, is the asthenosph...

## Major Landforms of the Earth ### Introduction The outermost layer of the Earth is a solid crust ranging in thickness from 5 km to 100 km. Below the crust is the mantle. The lithosphere includes the Earth's crust and the uppermost part of the mantle. Underlying the lithosphere, is the asthenosphere which is the weaker, hotter and deeper part of the upper mantle. ### Layers of the Earth | Layer | Description | Depth (km) | |---|---|---| | Lithosphere | Crust + uppermost solid mantle | 5 - 100 | | Mantle | | | | Outer Core | | 2900 | | Inner Core | | 5100 | The continuous units of landmass on the Earth's surface are known as continents and the large bodies of water that surround the continents are known as oceans. They include the seas. According to the 'Continental Drift' concept, all the separate continents that we know today had once been part of an earlier supercontinent called the Pangaea. ### Tectonic Plates So what caused the supercontinent to break up and start to drift apart? The Tectonic Plate theory explains this occurrence. The Earth's crust is broken into pieces (like a cracked egg shell) of rock called *tectonic plates* that sit on the molten interior of the planet. Some plates move in *opposite directions* (*divergent*), some plates *collide* (*convergent*) and some plates *slide past* each other (*transform boundary*). These movements have given rise to present day continents and some of the landforms seen on Earth. **Images:** - A cross-section of the Earth showing the layers, from the crust to the core. - A sequence of maps showing the break-up of the supercontinent Pangaea over millions of years. - A map of the Earth showing the different tectonic plates and their movement.