<P> Carbon is a key component of all known life on Earth, representing approximately 45 - 50% of all dry biomass . Complex molecules are made up of carbon bonded with other elements, especially oxygen and hydrogen and frequently also with nitrogen, phosphorus and sulfur . 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 frequently 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 . </P> <Table> <Tr> <Td> </Td> <Td> This section needs expansion . You can help by adding to it . (August 2015) </Td> </Tr> </Table>

Why is life on earth considered carbon based
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