Aight, so life has to start as tiny ass microbes. And in controlled situations (that\'s what makes it not so for sure), they were able to start life almost immediatley after getting all of the right conditions, which earth has.
So right when earth got all of its right ingrediants, life should form as tiny microbes very quickly. However, large asteroids still hit earth, big enough to wipe off any microbe life that existed. Then everything settles down (im oversimplifing it) and the conditions are still right for life so it should sprout up again very quickly. Rinse and repeat
these microbes arent evolving, and turning into fish. Theyre just the most basic forms of life getting wiped out as asteroids hit, but coming back when everything settles down