The Earth and Universe

The Layers of Earth and its Atmosphere

Rock Types

There are three types of rock:

• igneous rock
• sedimentary rock
• metamorphic rock

Igneous Rock

• These rocks are formed from cooling magma
• When magma gets forced up through the earths crust, it cools and solidifies and forms igneous rock (extrusive igneous)
• If the magma cools beneath the surface, intrusive igneous rock will form

The size of the crystals depends on how quickly the molten rock cooled:

• if it cools quickly, the crystals are small
• if it cools slowly, the crystals are large

Features of an Igneous Rock:

• hard
• randomly arranged, interlocking crystals of minerals
• crystals can be quite colourful

Sedimentary Rock

• These rocks are formed when transported and deposited sediments are compressed and therefore, the water is squeezed out from between the pieces of rock so that they are cemented to form a rock
• These rocks may have fossils of animals and plants trapped in the sediments as the rock is formed
• The oldest layers are at the bottom and the newest layers are at the top

Features of a Sedimentary Rock:

• separate grains of minerals
• layers
• fossils (sometimes)
• soft
• grainy

Metamorphic Rocks

• These rocks are formed as the Earth's movements cause sedimentary or igneous rocks to be deeply buried or squeezed. 
• Therefore the rocks are heated and put under great pressure
• The do not melt but the minerals that they contain are changed chemically, forming metamorphic rocks

Features of a Metamorphic Rock:

• hard
• consists of interlocking minerals
• crystals are usually alligned
• smooth
• can have layers

The Rock Cycle

Weathering

Rocks gradually wear away. This is called weathering. Weathering is the breaking down of rocks into smaller pieces There are three types of weathering:

• physical weathering
• chemical weathering
• biological weathering

Physical Weathering:

Physical weathering is caused by physical changes such as changes in temperature, freezing and thawing, and the effects of wind, rain and waves.

 Temperature changes:

• When a rock gets hot it expands a little, and when a rock gets cold it contracts a little.
• If a rock is heated and cooled many times, cracks form and pieces of rock fall away. 

Wind, rain and waves:

• …