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The planet on which we live and, as far as we know, the only planet in the solar system that has liquid water on the surface and supports life. The third planet from the sun, and the largest of the four inner planets (Mercury, Venus, Earth, and Mars), Earth is about 90 million miles (about 150 million kilometers) from the sun. It has a diameter at the equator of about 7,927 miles (about 12,762 kilometers), but is not perfectly round. The diameter from pole to pole is about 26 miles (about 42 kilometers) less than the diameter at the equator. Earth’s surface is about 30% land and 70 % water. Earth's atmosphere contains 21% oxygen, which we breathe in order to live, 78% nitrogen, and .9% argon. The other 0.1% consists of water vapor, carbon dioxide, and traces of other gases. Earth rotates on its axis in 23 hours, 56 minutes, and 4 seconds, and revolves around the sun in 365 days, 6 hours, 9 minutes and 10 seconds. Earth has one natural satellite, called the moon.