Carbon-based lifeform

Carbon-based lifeforms are forms of life, flora or fauna, which are composed majoritively of carbon. Class M planets are typically only capable of supporting carbon-based life.

In 2154 the starship ENTERPRISE NX-01 visited a class M planet which unusual harboured a silicon-based virus. As Trip Tucker was well aware, thanks to Exobiology 101, the fact the virus was silicon-based was also a problem for the carbon-based crew of the Enterprise as their immune systems could not fight off such an alien attack. Fortunately for Trip, who had been infected, a cure was found. 

In 2364, when the USS Enterprise (NCC-1701-D) was en route to planet T-B 13, some of the first information about the planet the Enterprise could detect was that it was carbon-based and class M.

In 2369, a Horta-Human mining operation on Lythos Prime was attacked by a Borg cube when its sensors, confused by kelbonite deposits, mistakenly detected what it thought was a carbon-based/silicon-based hybrid species on the planet. 

As of 2370 Starfleet tricorders were typically programmed to detect carbon-based life. They could also be set to detect silicon-based life, or both types working duel-function, but required specific recalibration to do so.