Tellurian can be used as an adjective to mean ‘of, inhabiting or relating to the earth’. Readers, writers and watchers of science fiction will probably be familiar with the noun meaning ‘an inhabitant of the planet earth’.
Tellus (or tellur) is the Latin word for earth or ground. Tellus is also the name of the goddess of the earth in Roman mythology or a personified version of the earth (usually female).
Tellurian was used to refer to the earth in the late 18th century, as shown here:
"It will show the heliocentric position of the telurian orb." A Short Account of the Solar System, Bartholomew Burges. 1789.
Its use to mean ‘a person from the planet earth’ was established and flourishing in fiction by the mid 19th century. The text the following example is taken from is available to read on Google Books:
[Spoken by the Man in the Moon] "What monster have we here?—Away, Tellurian!" Blackwood's Magazine, May p555. 1828.
Source: The Oxford English Dictionary (online)