Almost all life on Earth is part of a web that gets its energy ultimately from the Sun. Each life form in the web usually exchanges nutrients with other life forms. But, if the environment can supply basic needs, strange singular forms can exist independently of all other life and even of the Sun.
All cells must have three things to survive:
- Energy to run the activities of their cells (such as, combining nutrients to make sugar and thereby release energy).
- Liquid water to dissolve chemicals and allow them to mix together and react. "Liquid" because liquid water is the right temperature for essential chemical reactions to occur in cells.
- Chemical building blocks.
- ----- Carbon for its ability to form long chain-like molecules (like sugars and proteins). Every living thing on Earth is made from a set of molecules built around carbon atoms.
- ----- Hydrogen and oxygen to bond with carbon and also make water. By the way, of the approximately twenty-four atoms required, 95 per cent of the human body is made up of just four atoms (carbon, hydrogen, oxygen and nitrogen)
- ----- Nitrogen likewise to bond with carbon and also to bond with hydrogen and oxygen and form stable, large molecules.
- ----- Other elements: sulphur, phosphorus, sodium, potassium, magnesium, calcium, manganese, iron, cobalt, copper and zinc.
-
These creatures, over millions of years, evolved to use energy supplied from our planet rather than our sun.
Such organisms use inorganic chemicals (usually hydrogen and hydrogen sulfide obtained from rocks and sea water) for energy instead of organic matter. They utilize carbon dioxide as their carbon source.
