Water exists as a solid, a liquid and a gas. When you heat a metal, it expands. Steel is a mixture of iron and other substances. 4. Two-thirds of the earth’s surface is water. 5. The distance of the sun from the earth is 150,500,500 kilometres. 6. The earth is 4.6 billion years old. 7. The earth is forty-nine times larger than the moon.

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Introduction 1