P1

• The Earth is about 4500 million years old.
• Oldest rocks are about 4000 million years old.
• When it was first formed it was completely molten.
• We can tell how much it has changed through erosion, craters, mountain formation and folding.
• Further evidence of earths age. you can look at fossils and the radioactivity of rocks.
• Structure of Earth. Thin rocky crust, The mantle, The core.
• Crust; thickness between 10km and 100km, Oceanic crust beneath oceans, Continental crust forms continents.
• Mantle; extends almost halfway to center, higher density, very hot and under pressure.
• Core; over half Earths radius, very hot.

• Continental Drift theory proposed by WEGNER.
• it is that the continents fit together because the fossils, rock patterns and mountain ranges all match up.
• the theory was rejected by Wegner's peers because he wasn't a geologist, the supporting evidence was limited and the movement of continents wasn't detectable.
• Evidence from sea floor spreading lead to it becoming ACCEPTED.

Earths crust is cracked into several large pieces called tectonic plates.

They...

• float on Earths mantle because they are less dense.
• can move apart, towards or slide past each other.
• Lines where they meet are called plate boundaries.
• volcanoes, earthquakes and mountain formations, normally occur at plate boundaries.

A geohazard is a natural hazard. e.g. floods and hurricanes. some have warning signs.

Some strike without warning so precautionary measures need to be taken. for example; Buildings within earthquake zones are designed to withstand tremors. Authorities will often refuseplanning permission in areas prone to flooding.

The Mantle is fairly solid. It is just beneath the Earths Crust. Further down is Liquid.

• Convection currents in the mantle cause magma to rise.
• Convection currents move the solid part of the mantle and tectonic plates.
• where plates are moving apart, magma reaches the surface and hardens.
• this forms new ares of oceanic crust (seafloor) - and it pushes the existing floor outwards.

Earth's magnetic field changes polarity every million years and produces rock stripes of alternating polarity. These occur at constructive plate boundaries.

Subduction= the denser oceanic plate is forced under the continental plate. occurs at destructive plate boundaries.

mountain ranges form along colliding plate boundaries as sedimentary rock is forced up by collision.

Plate movement is crucial in the rock cycle.

The big bangtheory explains how the unvierse began.

• it says the unvierse began with a big explosion.
• 14000 million years ago.

The solar system formed 5000 million years ago.

• the solar system began as dust and gas clouds.
• nuclear fusion formed the sun.
• smaller masses like planets, moons, asteroids and comets formed around the sun.
• The sun's energy comes from nuclear fusion: hydrogen atoms fuse together.
• the nuclei of hydrogen fuse together during nuclear fusion.
• Other galaxies are moving away from us.

Hubble's law - the speed in which a galaxy is moving away is proportional to its distance. Space is expanding.

speed of light = 3000 000km/s.

Vast space distances are measured in light years.

The distance of a star can be measured using relative brightness or parallax.

stars produce radiation.

stars have a finite life and eventually become red giants or super red giants.