*I'm liking this cocktail-napkin apocalypse math, but I doubt that the oceans boiling would actually kill everything on Earth. A lot of stuff thrives in volcanic vents where the ocean is already boiling.
*The Earth being consumed by a red giant Sun in a billion years or so, that oughta do it.
*That's assuming, though, that the Earth hasn't already left a reeking trail of biological contagion, maybe magnetized or ionized spores that get lofted out of the atmosphere and blown into the galaxy by the solar wind.
*Or, imagine the Earth was coming apart in chunks as the Sun finally ate it. Wouldn't there be the likes of chemosynthetic tardigrades, kinda stuck safe in the deep subterranean rock pores? Wouldn't chunks of contaminated rock get flung out as unstable orbit debris? I don't wanna get all vitalistically mystical about the continuance of life, but the thought of absolutely wiping out all traces of Earthly life, it seems implausible, too antiseptic.
A supernova, a gamma ray burst, a stray asteroid runs into us, etc
