No more than evidence of life forming on earth which is zero. I've thought about it semi professionally for long, and my bet would be on panspermia. Heck, my be

No more than evidence of life forming on earth which is zero. I've thought about it semi professionally for long, and my bet would be on panspermia. Heck, my bet would be that all life in our galaxy is probably from the same origin; it seems fairly easy for at least some microbes to survive on rocks for really long periods of time, and my guess would be that once one form of life takes hold in a place other competing forms would probably get fully eliminated. Thus it stands to reason that panspermia is more probable. This is supported further by how quickly life seems to have appeared on earth the moment it was habitable (followed by how it took billions of years after that to evolve in any meaningful way).