The earth is one of the eight planets in the solar system, ranking third in the order from near to far from the sun. It is also the earth-like planet with the largest diameter, mass and density in the solar system, which is 65.438+0.5 billion kilometers away from the sun. The earth rotates from west to east and revolves around the sun at the same time. At present, there is a natural satellite-the moon, which forms a celestial system-the earth-moon system. It originated from the primitive solar nebula 4.6 billion years ago.

The equatorial radius of the earth is 6378. 137 km, the polar radius is 6356.752 km, the average radius is about 637 1 km, and the equatorial circumference is about 40076 km. It is an irregular oval sphere with slightly flat poles and slightly bulging equator. The surface area of the earth is 5 1 100 million square kilometers, of which 7 1% is ocean and 29% is land. Seen from space, the earth looks blue.

Extended data:

The structure of the earth:

1, atmosphere

The earth's atmosphere is the outermost gas layer in the outer circle of the earth, surrounding the ocean and land. There is no exact upper limit of the atmosphere, and there are still thin gases and elementary particles at an altitude of 2000 ~ 16000 km. There is also a small amount of air in the ground, soil and some rocks, which can also be considered as a part of the atmosphere.

2, hydrosphere

The hydrosphere includes oceans, rivers, lakes, swamps, glaciers and groundwater. This is a continuous but irregular circle. Overlooking the earth from a height of tens of thousands of kilometers, we can see the white clouds formed by water vapor in the earth's atmosphere and the blue ocean covering most areas of the earth, making the earth a "blue planet".

3. Biosphere

Due to the existence of minerals in the atmosphere, hydrosphere and surface of the earth, a natural environment suitable for living things has been formed under this suitable temperature condition on the earth. People usually refer to living things, including plants, animals and microorganisms. It is estimated that there are about 400,000 species of plants, about 165438+ 10,000 species of animals and at least 65438+ 10,000 species of microorganisms.

4. Lithosphere

For the earth's lithosphere, it is impossible to observe it directly except the surface morphology. It is mainly composed of the crust in the mantle circle and the top of the upper mantle, and extends from the solid earth surface down through the first discontinuity (Moho surface) shown by seismic waves at a distance of nearly 33 kilometers to the asthenosphere.

Baidu Encyclopedia-Earth