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Life on Earth
The Earth is very unique to our universe because it is the only planet known to have life . Our planet is the right distance from the sun so that it is possible for animals and plants to live. The first signs of life were blue-green algae and bacteria formed in the seas, and did not appear until 3.5 billion years ago. More complex plants and animals did not develop until 570 million years ago. There are about 1.3 million species of animals on Earth today and probably millions more that are unknown.
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