Carbon forms the key component for all known
life on
Earth. Complex
molecules are made up of carbon
bonded with other
elements, especially
oxygen,
hydrogen and
nitrogen, and carbon is able to bond with all of these because of its four
valence electrons. Carbon is abundant on earth. It is also lightweight and relatively small in size, making it easier for enzymes to manipulate carbon molecules. It is often assumed in
astrobiology that if life exists somewhere else in the
universe, it will also be carbon based. Critics refer to this assumption as
carbon chauvinism.