Our Earth
Earth, in geology and astronomy, the fifth largest planet of the solar system and the only planet definitely known to support life. Gravitational forces have moulded the earth, like all celestial bodies, into a spherical shape. However, the earth is not an exact sphere, being slightly flattened at the poles and bulging at the equator. The equatorial diameter is 12,760 km and the polar diameter 12,720 km; the circumference at the equator is 40,000 km. The surface of the Earth is divided into dry land and oceans, the dry land occupying million 148.9 million sq. km, and the oceans 361.3 million sq. km. The earth is surrounded by an envelope of gases called the atmosphere, of which the greater part is nitrogen and oxygen. The Geologic Earth Knowledge of the earth’s interior has been gathered by three methods: by the analysis of earthquake waves passing through the earth, by analogy with the composition of meteorites, and by consideration of the earth’s size, shape, and density.
