Earth Science

→ The earth’s internal structure can be classified in 2 ways:

• Chemical composition: Crust, Mantle and Core (Iron/Nickel).

• Mechanical composition: Lithosphere (including all crust + upper mantle) and Asthenosphere.

→ The earth’s crust:

• It contains relatively light (less dense) materials with low melting points. These are mostly compounds.

• Divided into 2 categories: oceanic crust - thinner but denser than continental crust and supports the earth’s oceans. Much younger. continental crust - rises higher than oceanic crust and is thicker but less dense + makes up the continents. Much older.

→ Differences between the oceanic and continental crust:

→ The earth’s mantle:

• The mantle is the material left in the middle zone after most of the heavy material sank, and the light material rose towards the surface, and forms the majority of the planet.

• Consists of rock of intermediate density, mostly of compounds of oxygen, with magnesium, iron and silicon.

• The outermost part is rigid and strong (referred to as the lithosphere) but at a high depth, the rock partially melts as a result of heat.

• Huge convection currents cause the crust to move (plate movement).

→ The earth’s core:

• Consists mainly of iron which would have sunk to the centre of the earth during the process of differentiation.

• Subdivided into a solid inner core which rotates in a molten/liquid outer core. The solid inner core is very hot but it’s solid because of the sheer pressure of the rest of the earth’s layers (mantle and crust), which prevents melting to occur. The inner core is made mostly of iron, whereas the liquid outer core is made of iron and nickel.

• Since it consists of iron/nickel (metals have loose electrons), the outer core is responsible for the earth’s magnetic field. It’s semi-solid.