Language Rant: When to Capitalize the Initial Letter in 'Earth'

I found the following sentence in David Benatar's The Human Predicament, p. 36:

Nothing we do on earth has any effect beyond it. (36)

This sentence slipped past the Oxford editors. The initial letter of 'earth' ought to be capitalized since the word is being used as the proper name of a planet.  A while back, Cher threatened to leave for Jupiter, not jupiter, should Trump win the election.  Men are from Mars, not mars, and women from Venus, not venus. 

Mons veneris, however, is from the proper name of the goddess of love, not the planet. You know what it means and you know that it does not refer to an extraterrestrial  geological formation.

But if you are talking about dirt or soil or the mythical Aristotelian element, then write 'earth.' The lower case is also employed in such expressions as 'What on earth are you saying.'

The same goes for such expressions as 'She's not long for this earth.' When a person on Earth dies, his body does not leave Earth. But he leaves the world in one sense of 'world.' Sic transit gloria mundi.

Watch it, ragazzi, else I'll sic my cat Heinrich on you.