I agree that evolution describes how life advances, but given that DNA...

Pan DNA is more likely about 94% that of Homo DNA and not 98% no matter how you measure it.

It's pretty clear RNA was first although I don't know if DNA evolved from it or evolved separately.

 

There is a BIG reason why most scientists don't accept panspermia, and that's because there is no proof that life even exists beyond our planet. This is the same problem with Creationism/ID, until one can prove that an Intelligent Designer exists, it is not a valid theory. Now, if we ever find life somewhere else in the universe, I have no doubt the panspermia will become more accepted, even though it still has other issues it needs to address.

 

The OP assumes life began on this planet, when we see vast clouds of organic molecules out in space.

http://www.bbc.co.uk/news/science-environment-29368984