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Almost all the energy on the earth comes from the sun. Heat from the sun makes the earth warm enough for life. Plants use the sun's energy to live and grow. Plants give off a gas called oxygen. Animals eat plants and breathe oxygen. Animals need plants in order to live, and plants need the sun. You use plants to create heat and energy. You can burn wood from trees. You can burn fossil fuels called coal, gas, and oil. Fossil fuels formed deep underground from plants and animals that died millions of years ago.

The sun's energy can also do harm. Too much sunlight can burn your skin, causing sunburn. Harmful rays from the sun can also cause a disease called skin cancer. Looking right at the sun can harm your eyes. You need to be careful of the sun. The center of the sun is called the core, which is extremely hot. All the energy of the sun comes from the nuclear reactions in its core. It takes a long time for the energy from the core to reach the surface of the earth - about 170,000 years!