Life could never have existed on Earth without the proper conditions in the air, land, and water. For example, if the air became very cold all over the Earth, the water in the hydrosphere would freeze.

Frozen water is useless to living organisms because they cannot drink it, swim in it or search for food in it.

From this example, it is clear that temperature is an important factor in the environment. Temperature can be changed by changes in the atmosphere. For example, if there are many clouds during the day, the temperature will tend to be low. Therefore, the amount of sunlight is another important factor in the environment. 

If there is too much sunlight and the air is very dry, as in the case of a hot desert, very few organisms can survive. If a particular region receives an adequate amount of rainfall, however, it will maintain a good level of humidity. Humidity is the amount of water vapor in the air.