All life forms (on earth) rely on carbon (chemical symbol "C") for their existence and functioning. From miniscule bacteria to giant sequoia trees, from worms to whales, no life on earth including humans would exist without "carbon" in various combinations with other elements, most notably hydrogen, oxygen, nitrogen, and phosphorus.
Recent news speculate about hypothetical types of biochemistry and extraterrestrial life forms using a "silicon" based system, possibly akin to the Caltech artist's rendering of such an envisioned life form shown nearby:
