Why is there life on Earth?
Earth is the only planet in the Solar System where life exists because a series of circumstances allow it:
- Mild temperatures. The average temperature of the planet is 15 ºC, so the water is mainly in a liquid state. Living beings need water, since all the chemical reactions of metabolism are carried out in it . Earth has these mild temperatures because of:
- The proper distance from the Earth to the Sun, an external energy source that emits energy that reaches the Earth in the form of light and heat.
- Existence of a greenhouse effect. The atmosphere has gases such as carbon dioxide (CO2) and water vapor (H2O) that retain the heat that is reflected by the Earth and makes the temperature higher than it would be without these gases.
- Existence of atmosphere. The mass of the Earth is the appropriate one, corresponding to the appropriate size. If the Earth were smaller, its mass would not create enough gravity to hold the atmosphere down, and if it were larger, gravity would make the atmosphere so thick and dense that it would not allow sunlight to pass through. Thus, the atmosphere lets in the light with which plants can carry out photosynthesis and filter, in the ozone layer, ultraviolet radiation that is harmful to living beings. Also, the atmosphere contains oxygen necessary for the respiration of all living beings. In addition, the atmosphere also contributes to temperatures not being so hot in the equatorial zones or so cold in the polar zones, softening the temperatures. The existence of gases such as oxygen and carbon dioxide is essential, since they are necessary for respiration and photosynthesis.
- The presence of water on Earth, in addition to being used in cellular processes, also acts as a temperature regulator.
- The abundance on the earth's surface of some chemical elements, such as carbon, nitrogen, phosphorus, etc., allows them to combine to form the biomolecules that constitute living beings.
- The existence of a magnetic field that protects living beings from harmful solar radiation.
- The Earth serves as a support for living beings. Many animals live inside or on the ground, in addition to the fact that plants take water and mineral salts from the soil.