Everything about Carbon-based Life totally explained
Carbon forms the backbone of
biology for all
life on
Earth. Complex
molecules are made up of carbon
bonded with other
elements, especially
oxygen,
hydrogen and
nitrogen. It is these elements that living organisms need, among others, and carbon is able to bond with all of these because of its four
valence electrons. Since no life has been observed that isn't carbon-based, it's sometimes assumed in
astrobiology that life elsewhere in the
universe will also be carbon-based. This assumption is referred to by critics as
carbon chauvinism, as it may be possible for life to form that isn't based on carbon, even though it has never been observed.
In cinematic and literary
science fiction, a moment when man-made machines cross from nonliving to living is often posited, this new form being the first example of non-carbon-based life. Since the advent of the
microprocessor in the late 1960s, these machines are often classed as
computers (or computer-guided
robots) and filed under "
silicon-based life", even though the silicon backing matrix of these processors isn't nearly as fundamental to their operation as carbon is for "wet life".
Characteristics of carbon as a basis for life
The two most important characteristics of carbon as a basis for the
chemistry of life are that it has four valence bonds and that the energy required to make or break a bond is just at an appropriate level for building molecules which are not only stable but also reactive.
The fact that carbon atoms bond readily to other carbon atoms allows for the building of arbitrarily long and
complex molecules.
There are not many other elements which appear to be even promising candidates for supporting life-like behavior, but the most frequent alternative suggested is
silicon. This is in the same group in the
Periodic Table of
elements and therefore also has four
valence bonds. It also bonds to itself, but generally in the form of
crystal lattices rather than long chains. However, its compounds are generally highly stable and don't support the ability to readily re-combine in different permutations in a manner that would plausibly support life-like processes.
This speculation of a life based on the chemistry of
silicon is clearly distinct from "
silicon-based life" in the above sense of
artificial intelligence based on electronic processes utilizing
silicon integrated circuits.
Key carbon-based molecules in the life processes
The most notable groups of chemicals used in the processes of living organisms include:
- Proteins, which are the building blocks from which the structures of living organisms are constructed
- Nucleic acids, which carry genetic information
- Enzymes, which catalyse organic chemical reactions
- Carbohydrates, which store energy in a form that can be used by living cells
- Fats, which also store energy, but in a more concentrated form, and which may be stored for extended periods in the bodies of animals.
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