(May 22, 2017 at 1:24 pm)Whateverist Wrote: But that only supports the notion that life arising on other planets may wind up on planets where life has already arisen. If the conditions are right to support the alien forms, it would probably also initiate abiogenesis here.
Not necessarily. We don't know on average how long it takes for abiogenesis to occur in environments that otherwise could have sustained life that has already arisen. It could be hundreds of millions of years. The earliest evidence of life on earth seem to postdate the earliest evidence of relatively mild conditions on earth by 300-500 million years. That's a period of time roughly equal in length to that between Cambrian explosion and now. So if abiogenesis were to be allowed to occur on all bodies in the solar system where they can occur, their timing may still differ by hundreds of billions of years or even billions of years.
I have seen estimates that says ejecta from major meteoritic impact on a large rocky body in the solar system will typically take 30 million years before accreting onto another major body. Another study say that during the 100-200 million years before first evidence of life on earth, inner solar system experienced a particularly severe period of meteror bombardment during which major impacts capable of ejecting debris at escape velocities of rocky planets and moons occur on average once every 100 years on each major inner solar system bodies.
So the upshot seems to be there is plenty of time and opportunity for the products of earlier abiogenesis in the solar system to get blasted from the body of their origin, travel through solar system, and land on another body long before native abiogenesis has occurred on the other body.
We don't know how long it takes for new life introduced to a hospitable environment to propagate through all the available niches at the destination planet and potentially forestall or severely constrain an successful independent abiogenesis event on the destination planet. But even if that takes many hundreds of millions of years, it still does not seem statistically prohibitive for such panspermia to have snuffed out many potential abiogenesis evens in our solar system.
