But what about before that?

There's no such thing as a "law of biogenesis". The solar system did not originate from the Big Bang. The two are not closely related in time at all. The Big Bang was about 13.7 billion years ago, the origin of the solar system eons later about 4.6 billion years ago. The solar system condensed from nebular material sitting around in space, at least some significant portion of it having been scattered into space from earlier generation stars that went supernova.Both Uranus and Venus rotate in the opposite direction from other planets, but you're probably thinking of Uranus since you mention a collision. It isn't Uranus's direction of rotation, but it's unusual tilt (about 98^o), that caused scientists to propose a collision early in it's history as one possible explanation. The collision would not cause a permanent dent. Objects of planetary scale are very plastic and will always quickly return to a substantially spherical shape. The moon is thought to possibly be the result of a collision of a large object with the earth very early in our history, and there is no dent on earth, either. The first life would have been very simple, a single-celled organism perhaps something like blue-green algae. It would have been the product of a long series of small, incremental stages over many millions of years. This is a fairly speculative area as there is much we don't know about the early earth, but there is no requirement that the first life evolved on the planet's surface. If radiation was a problem then the first life probably came about either underground or beneath the surface of water.--Percy