what is essential for the life to exists.
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Answer:
It is useful to categorize the requirements for life on Earth as four items: energy, carbon, liquid water, and various other elements.09-Jun-2014
Liquid water: Rare, only on Earth for certain
Energy: Common
N,P, S, Na, and other elements: Likely to be common
Our understanding of life on exoplanets and exomoons must be based on what we know about life on Earth. Liquid water is the common ecological requirement for Earth life. Temperature on an exoplanet is the first parameter to consider both because of its influence on liquid water and because it can be directly estimated from orbital and climate models of exoplanetary systems. Life needs some water, but deserts show that even a little can be enough. Only a small amount of light from the central star is required to provide for photosynthesis. Some nitrogen must be present for life and the presence of oxygen would be a good indicator of photosynthesis and possibly complex life.