Earth's Crust, Lithosphere and Asthenosphere

• Earth has four main layers: the inner core, outer core, mantle, and crust.

Earth's Crust

• The Earth's crust is thin compared to the other three layers and makes up 1% of Earth's volume.
• The outermost layer is the crust.
• The Earth's crust is broken into many pieces called plates.
• The crust's thickness varies, under mountains, it can be 40-70 km thick, but less than 7 km under the ocean.
• The crust is the least dense of all layers.
• Silicon and oxygen make up the crust.
• Oceanic crust is very dense and made of basalt.
• Continental crust is less dense and made of granite.
• Sima is a dense material forming part of the oceanic crust and also the lower part of the crust beneath the continents; it is made of silica and magnesium.
• Sial forms the upper part of the continental crust and is composed of lighter rocks; Sial floats on the denser material beneath and is made of silicon and aluminum.

Lithosphere and Asthenosphere

• The lithosphere consists of the Earth's crust and the very top part of the mantle.
• The asthenosphere is a layer right below the lithosphere in the upper mantle and has qualities of a thick paste, it is not a liquid or a solid.

Earth's Mantle

• The mantle is the layer below the crust.
• The mantle makes up 85% of the Earth.
• The mantle is about 2,900 km thick.
• The mantle has upper and lower sections.
• The mantle is made of hot softened rocks with more magnesium and iron.
• Density increases with the depth of the mantle due to an increase in pressure; it is less dense near the crust and more dense near the core.
• A convection current in the mantle is caused by heat from the core.
• Magma rises inside the mantle due to heat, and when it reaches the lithosphere it cools, moves horizontally, and sinks back to the mantle.
• The tectonic plates move because of this process.

Earth's Core

• The core constitutes 15% of the Earth.
• The outer core is liquid and is made up of iron, nickel, and sulfur.
• Earth's magnetic field is inferred to be caused by movement of materials in the liquid outer core.
• The outer core is very dense.
• The solid inner core is made up of iron and nickel.
• Metals in the inner core are squeezed together due to high temperatures and pressures, so they are not able to move.

Earth's Magnetic Field

• The outer core spins faster than the inner core, and molten iron flows, this creates the magnetic field.
• The magnetic field acts like a bar magnet with opposite poles.
  • North attracts South
  • South attracts North
• The compass will point to geographic north (magnetic south) because of the magnetic forces.