The age of the Earth
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The main layers
of the Earth
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All our evidence for changes in the Earth comes from looking at rocks. Folds and fossils in sedimentary rocks, radioactive dating and the weathering of ancient craters show that the oldest rocks are about 4000 million years old. That means the Earth must be at least as old as this.
Structure
The only thing that we have been able to observe directly is the Earth’s crust, which is the very thin outer rocky layer.
Evidence from earthquakes shows that the Earth has a very dense core surrounded by a solid mantle.
The Earth is almost a sphere. These are its main layers, starting with the outermost:
- the crust, which is relatively thin and rocky
- the mantle, which has the properties of a solid, but can flow very slowly
- the outer core, which is made from liquid nickel and iron
- the inner core, which is made from solid nickel and iron
Note that the radius of the core is just over half that of the Earth.
[ This page has been adapted from www.bbc.co.uk/schools/gcsebitesize/science
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