Earth
one of the planets in the solar system, the third in distance from the sun and the fifth largest of the planets in diameter. the mean distance of the earth from the sun is 149,503,000 km 92,897,000 mi. it is the only planet known to support life, although some of the other planets have atmospheres and contain water.
the earth is not a perfect sphere but is slightly oblate, or flattened at the poles. the diameter of the earth measured around the north pole and the south pole is about 42 km 26 mi less than the diameter of the earth measured at the equator.


composition the earth consists of five parts the first, the atmosphere, is gaseous the second, the hydrosphere, is liquid the third, fourth, and fifth, the lithosphere, mantle, and core, are largely solid. the atmosphere is the gaseous envelope that surrounds the solid body of the planet. although it has a thickness of more than 1100 km more than 700 mi, about half its mass is concentrated in the...