Actually, you can. And we have discussed why at some length.
Recall that we have been using an analogy of trying to determine whether the man standing in front of you is in fact 30 years old, or whether he was miraculously created a minute ago with a mere appearance of age.
In the same way, we are discussing in this thread whether the earth we inhabit is truly 4+ billion years old, or whether it was created merely 6000 or so years ago with the apparent age of 4+ billion years.
How would we determine whether the man standing in front of us was truly 30 years old rather than created ex nihilo a minute ago? Here’s one way: Check his arms and hands for scars. If you see numerous scars, you would conclude that they point to events (wounds) that occurred months or years ago. The scars would help you decide that the man is well and truly 30 years old, and not created ex nihilo a minute ago with an apparent age.
In the same way, fossils point to events that happened millions and billions of years ago. At one point you seemed to think that fossils could not be dated by any method other than radiocarbon (maximum span of 50k years), but in your last post you grasped that the fossils point to lives lived in deep time, just as the radiometrically dated geological strata that sandwich them were formed in deep time.
To summarize:
- The radiometric dating of geological strata tells us an age of billions of years.
- The fossils (are like scars that) tell us that the age is real, not merely apparent.
Peace,
Chris