Basically, it's the cesspit where we all come from. Millions of years old, it gets occasionally disinfected by an ice age or a KT-event, though some might prefer that to happen a bit more regularly. We like to think that we're floating about somewhere at the deep end of it, though that's probably just our human egotism speaking -- the selfish gene, again.

Generally speaking, it smells and is in dire need of a chlorine treatment.