Among the nine planets in the solar system, the light blue earth is the only planet full of life. In its mountains, oceans, forests, blue sky and poles, there are nearly two million kinds of creatures. It is a well-deserved paradise for life. However, why does life love earth so much?

Although the academic circles can't give an accurate definition of life at present, life is a complex phenomenon, which has two basic characteristics: first, it can replicate itself; The second is to be able to metabolize. Both activities require energy. As far as animals and plants are concerned, the ultimate source of energy is the sun.

If the planet is too far away from the sun, such as Pluto, it receives little sunlight, just like the legendary underworld, life can't survive because it can't get enough energy; If the planet is too close to the sun, such as Venus, receives a lot of sunlight, and the temperature is above 400 degrees day and night, just like the mythical purgatory, it is difficult for life to survive.

The earth is neither too close nor too far from the sun, and receives moderate light. Plants can freely use solar energy for photosynthesis and store the energy needed for life activities. When vegetarians eat plants, this stored energy will reach vegetarians, and when carnivores eat vegetarians, the energy will reach carnivores ... in this way, it is the light of the sun that can start the life machines of animals and plants on the earth and make their descendants flourish.

Suitable temperature on the earth is necessary for life activities. The energy needed for life activities is provided by metabolism. Too cold or too hot environment is not conducive to normal metabolism. Only at a suitable temperature can plants carry out photosynthesis effectively.

The earth is protected by the atmosphere, which is by no means necessary for the life living in it, because: the atmosphere blocks the strong ultraviolet rays from space, so that life on earth is not harmed; The atmosphere blocks most meteorites that hit the earth, and the surface of the earth is not as uneven as the surface of the moon; The atmosphere is like a thick quilt, so that the sunlight shining on the earth's surface will not be emitted into space, and the temperature on the earth will not change dramatically; Without the protection of the atmosphere, there would be no wind and rain on the earth, and there would be no rivers, lakes and seas. The earth will be a dead and desolate planet.

There is a prosperous life on the earth, which is inseparable from its being a rocky planet. The core is molten magma, and its main component is iron. During the rotation of the earth, the iron core produces a strong magnetic field. This magnetic field surrounds the earth and protects it. When a solar storm, that is, a high-speed charged particle stream from the sun violently hits the earth, the magnetic field around the earth blocks it in space, thus protecting life on the earth.

For life, the conditions on the earth are unique. However, in the vast universe, the solar system is just a drop in the ocean, and the sun is not the only star in the vast universe. Is the earth the only living planet in the vast sea of stars?