Slate is formed as mudstone gets heated and compressed and its tiny plate-like-particles get aligned in the same direction. Slate is then useful for roofing tiles as the rock can be cut along the direction of the particles.
Marble is formed from limestone. Very high temperatures break down the shells in limestone and they reform as small crystals. This is why marble has an even texture and a lot more dense. The great texture is why marble has been able to be used to decorate easily.
Schist is formed when Mudstone gets really hot. It is essential for there to be plenty of pressure, but at the same time not too much heat. New minerals are formed as the process takes place. As the schist is formed new inter-locking layers or crystals form.
Igneous Rock
The second type of rock is igneous rock. Igneous rock is formed when molten magma pushes up into the crust or right through it. Igneous rock contains various different minerals which act as interlocking-crystals. There are two types of igneous rock extrusive and intrusive. Intrusive igneous rock cools slowly with big crystals and extrusive rocks cool quickly with small crystals.
Granite is an intrusive rock formed under the ground where magma cools down slowly. This means it has big randomly-arranged crystals, because it cools down slowly. Granite is a very hard stone suitable for steps and buildings.
Basalt is an extrusive igneous rock with small crystals. It is formed on the top of the earths crust after bursting out of a volcano. This means it has relatively small crystals, because it cooled quickly.
The Rock Cycle
Rocks change from one to another in a slow cycle named the rock cycle. This begins as particles getting washed to the sea and then settling as sediment.
Over millions of years the sediment gets crushed into sedimentary rock. The rock can either rise to the surface or sink down lower through the see bed to the heat ad pressure below.
If the rock descends lower the structure of the rock will be completely altered and become metamorphic rock.
Then again the metamorphic rock can either rise to the surface or descend further where it will become magma.
When magma reaches the surface it cools and becomes igneous rock, extrusive rock comes straight out of the volcano, but intrusive rock sets below as a big bump below the surface.
When all of the rock reaches the surface, the weathering will begin to gradually wear down the rock and it will be carried of to the sea.
The process then starts again at the beginning.
Weathering/Water cycle
Weathering is the process in which rocks are broken up and worn down. There are three types:
Physical weathering which is caused by the ice in the cracks of rocks. This is where rain water floods into the cracks in the rocks, and when the temperature drops below zero the water turns into ice, as the water freezes the expansion pushes the rock apart. This happens repeatidly until the rock is pushed apart enough for a piece to break off.
Chemical weathering is caused by acid rain onto limestone. All rain is a very weak acid, so very slowly it will dissolve the limestone.
Biological weathering which is caused by plant roots in the cracks of rocks. Plants push their roots into the rocks, they gradually push the rocks apart.
Erosion and Transport
Erosion is the wearing away of exposed rocks. It is different though from weathering.
Transport is the process of carrying away rock fragments, either due to gravity or down rivers. As the rocks travel down rivers, they get worn down.
The water Cycle
The Earths Structure
The earths crust is very thin.
The mantle is liquid but very viscous.
The core is just over half the Earths radius.
The core is made from iron and nickel.
This is where the Earth’s magnetic field originates.
The iron and nickel sank to the bottom long ago, because they’re denser.
The core has a solid inner bit and a liquid outer bit.
Radioactivity decay creates all the heat inside the earth.
This heat causes the convection currents which cause the plates of crust to move.
The overall density of the earth is higher than rock, which means the earth must be made out of something denser than rock.
Meteorites which crash into the earth are often made of iron and nickel. Ron and nickel are both magnetic and very dense. So if the core of the earth was made of iron and nickel it would explain everything such as the magnetic field and the very high density.
The earth’s surface is made up of large plates of rocks. These plates are like big rafts that float across the liquid mantle. As the rafts move the continents move to. The average speed of the plates is 1.5 cm per year.
Evidence for plate tectonics:
There is a very obvious jigsaw fit between Africa and south America. The other continents can also be fitted in without too much trouble. Its widely believed that they once formed a single land mass, called the Pangaea.
Matching fossils in Africa and South Africa. Identical plant fossils of the same age have been found in rocks in South Africa, Australia, Antarctica and South Africa, which strongly suggests they were all joined up. Animal fossils support the theory too. There are identical fossils of a freshwater crocodile found in both Brazil and south Africa. It certainly didn’t swim across.
Living creatures found in both America and Africa. One such beastly is a particular earthworm which is found living at the tip of south America and the tip of south Africa.
Identical rocks of similar ages are studied in various countries they show similar remarks. This is strong evidence that these rocks were once joined.
The symmetrical pattern of magnetic rocks on the ocean floor either side of the Mid-Atlantic ridge. This is clear evidence that the two sides are splitting apart. These magnetic stripes were only discovered in the 1960’s.
Plate Boundaries.
Plate boundaries are between tectonic plates, they’re usually trouble like volcanoes and earthquakes there are three different ways that plates interact: Colliding, separating and sliding past each other.
Oceanic and continental plates sliding past each other. The oceanic plate is always forced underneath the continental plate. This is called a subduction zone. As the oceanic crust is pushed down it melts and pressure builds up due to all the melting rock. This molten rock finds its way to the surface and volcanoes form. There are also earthquakes as the two plates slowly grind past each other. A deep trench forms on top of the ocean floor where the oceanic plate is being forced down. The continental crust crumples and folds forming mountains at the coast.
When two continental plates collide and meet head on. Any sediment layers lying between the two continent masses get squeezed between them. These sediment layers inevitably start crumbling and folding and soon form into big mountains. The Himalayan Mountains are an example of this.
Sea floor spreading. When tectonic plates move apart, magma rises up to fill the gap and produces new crust made of basalt. The mid-atalnatic ridge runs the whole length of the atlantic and actually cuts thorugh the middle
