Rocks, Weathering and

By Oscar Wooding, John scarfe, Sid Bhagat and Kofi Bruce, 8P

Sedimentary rocks formed over millions of years.

In the rock cycle igneous rocks are formed when molten magma cools. Erosion by the weather breaks these rocks up. The rivers and seas make layered sedimentary rocks.This gets buried, heated and squashed to metamorphic rock.

When rivers run fast hey carry bits of rocks of different sizes with them. As they slow down near the sea, the big bits settle at the bottom, but the sand is still carried along. At the sea the flow stops and the sand, silt and mud settle out.

Here is a diagram of how sedimentary rock is formed

Fossils: Sedimentary rock is often created gently as slow deposits of silt are gradually compressed and solidified . Its an ideal environment to preserve a record of the past. Using the fossil record of the past to find out what happened leads to interesting questions.

Fossils are formed in the following ways:

1) The animal or plant dies and its remains fall into the sediment.

2) Soft parts decay, leaving just the harder material.

3) Sediments form their layers round the harder material.

4) Over a long period of time, the plant or animal remains are replaced by deposits of minerals in the rock.

5) The mineral deposits exactly match the shape of the plant and animal remains.

6) The sedimentary layers are exposed at the surface.

A fossils of a plant that has been preserved in sedimentary rock for millions of years

The Ever changing planet

The earths face wasn't always as you'd expect, 300 million years ago a 'super continent' named Pangaea covered a small portion of the earth.

This image shows the the change in the continents positions over millions of years

Modern scientists believe that Pangaea was a reality, because many of the current continents seem to fit together like a puzzle, for example South America and Africa appear to convincingly fit together. But why has Pangaea split up into the continents we know today?

The rock surface of the earth is at most 10 kilometers thick. This is a planet that is nearly 1200 kilometers in diameter, so that is less than 1 hundredth of the thickness of the globe is solid crust. Beneath the rocky surface is a hot liquid called magma. It's temperature can be as hot as 1400 degrees Celsius.

In the vast volume of magma, convection currents move the rock about slowly, like jam. These currents carry streams of rock around under the surface. The movement in the mantle pulls the surface crusts with it.

Weathering and erosion

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