Mini_Dikta,
Do we know that dating is accurate because we always find the same fossils in the same layers?
No. We can have confidence in dating methods because different labs & methods arrive at similar conclusions.
You are getting confused with the concept of index fossils I think. Index fossils are numerous & widespread fossil species that are found in a narrow age range. The range is determined via radiometric dating. If the species actually does turn out to have a narrow age range after many tests, then we can with some confidence assert that any rocks we find them in are of that age.
For example, if the age of the surrounding sediment and/or rock in the area of a T-Rex find approximately matches that of the vast majority of other T-Rex finds (hopefully in disparate locations) it would seem to me that we now know with good certainty the approximate age of the T-Rex fossils. Is this a decent layman's explanation of how this dating works?
Yes, a reasonable explanation, but T-Rex would make a bad index fossil. Too few examples of this species.
Mark
There are 10 kinds of people in this world; those that understand binary, & those that don't
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