"repeatable science that is observable, not that which is not observable"

we are getting closer to the crux of the issue...

the study of life on earth had two important componants:
1)natural history as observed today and 2)as inferred, based upon historic evidence.

a simple example... pete lives in England and his monarch is currently Queen Elizabeth II. he could go to London & see her ride by or whatever... directly observable, after a fashion. It could be her doppleganger, but probably not.

now we go to historic evidence not observable... the first Queen named Elizabeth lived some 4 centuries ago... nobody alive today ever saw her... BUT... there are public records, paintings and various first hand written accounts that support the historic fact of her existence. In fact, we can use scientific means to determine if a document is actually authentic and not a fake based on the age of the paper and ink used and if it is consistent with what was available back then.

The same kind of scientific methodlogy is used when working on the geologic record that supports the theory of evolution. It is not a complete record... but then again, do we actually know every detail of Elizabeth I's life? No, but we do know enough to accept the reality of her existence and how long she was around.

There will never be a complete picture of the past, but that in and of itself does not negate what we do know. The fact of earlier life forms is as valid as the existence of the Tudor family line... while it lasted.