Driven wild by lust, the sort which might only be tasted by those who have sat in the company of the Olympian gods—masters of lubricity (as they are of all things)—an oft-tormented Poseidon saw fit to thrust his monstrous member into a volcanic crevice at the bottom of the sea whence he proceeded to thrust into the Earth Mother Gaia with a powerful and reckless enthusiasm that far from being within the author’s power to conjure up an image of, can be better understood by forgoing any nuance or explanation (save some developments within the vicinity of the action.)
At some instant of time, Poseidon completed his task whereupon he, in a state of disillusionment and shame, fled to an island where he stole himself away from the indignity of swimming in a vast ocean of his own discharge. So prodigious was this explosion of sexual energy that it filled the earth and made volcanoes and geysers and all manner of lesser vents to erupt from one end of the Earth to the other. From this unconsidered action, as well as from the labor of the Earth Mother, were made all the creatures of the sea which, over the course of eons, found their way to land and grew into all manner of sizes and shapes.
TLDR: life was created because a sexually frustrated Poseidon ejaculated into a sea-bottom crevice. Gaia (the Earth Mother) then gave birth to all life which evolved from that point.
If you think this story is ridiculous, consider the traditional accounts of the Big Three monotheisms and you might grasp that my explanation is literally less ridiculous than the absurd notion that some wizard man in the sky created us as we are this very moment!