The biosphere is a unique sphere that exists only on earth among all the planets in the solar system. It is a zone where the atmosphere and land and sea contact each other. It is covered with animals, plants and microorganisms, with a thickness of about 20 kilometers.
In the solar system, why only the earth has biosphere, and other planets don't even have life. Why are there no biosphere on other planets in the solar system? This should start with the conditions for the existence of life.
1. The existence of life requires proper temperature. If the temperature is too high, the atoms move too strongly and it is difficult to polymerize into molecules; If the temperature is too low, proteins and nucleic acids will freeze up and there will be no life. From the perspective of temperature, the distance between the earth and the sun is unique. The average temperature of the earth's surface is about 22 degrees Celsius, most of which are suitable for the growth and reproduction of life. Among the planets in the solar system, the earth's close neighbors are Venus and Mars. Venus is closer to the sun than the earth, and its surface temperature is about 400 degrees Celsius higher than the earth; Mars is farther from the sun than the earth, the surface temperature is 40 or 50 degrees lower than the earth on average, and the temperature difference between day and night is large. Other planets, either closer to the sun than Venus or farther away from the sun than Mars, do not have the temperature conditions suitable for life.
2. The existence of life needs liquid water. There is a lot of water on the earth, and most of the water is liquid. On other planets, even water is not liquid.
3. The existence of life requires an atmosphere with appropriate thickness and density to protect life from cosmic rays and provide an appropriate amount of free oxygen. The earth's atmosphere meets this condition. Other planets, such as Venus, Mars, Jupiter, Uranus, Neptune, and even Saturn's sixth moon, have atmospheres, but the atmospheres of these planets or satellites have little oxygen, so even if some form of life may appear on these planets, it can only be extremely primitive.
According to the above analysis, such biosphere on earth is unique in the solar system. However, many people believe that in the vast universe, there are celestial bodies with biosphere, and even celestial bodies with high intelligent life like human beings.