Re: [asa] geological dating

Moorad asked:

 I have often heard that geological dating is based on the supposition of
> evolution. Therefore, the fossil is dated by the age of the geological
> strata and conversely. Is that so?
>

No, absolutely not. The construction of the geological time scale was a
consequence of a number of developments over several centuries. The first
important step was the recognition by Steno (1638-1686) who, in trying to
explain the organic origin of fossils, developed the stratigraphic
principles of original horizontality and superposition that turned the
stratigraphic rock record into a timeline. Those layers that lie deeper
were deposited earlier. These principles enabled geologic events to be
placed in chronological order. Later Cuvier (1769-1832) demonstrated the
reality of extinction and showed that the further in the past one goes
(lower in the geologic column) the more different fossil species are from
those living. In other words, a directional history of life was now
superimposed on the history of the Earth. That history also extended back
in time well before the existence of humans. Cuvier along with others in
the early 1800's also recognized the fossil succession -- that the temporal
order of fossils in the fossil record is consistent from place-to-place.
Thus the types of fossils present in a stratum indicate the relative
position of that stratum in the geological column. This recognition allowed
geological strata to be correlated and mapped for the first time. Within a
very short time after this realization, the general outline of the
geological periods was established. This was largely completed by 1840. It
is very important to note that the individuals involved in the construction
of this relative geological time scale accepted the fixity of species and
were opposed to evolutionary ideas. Sedgewick and Murchison were two of the
primary individuals involved in this work. By this time there was also very
widespread recognition that the Earth's history of very long indeed.
However, no reliable method was available for assigning actual dates. What
existed was a relative time scale without dates. A reliable method for
dating did not exist until the discovery of radioactive decay at the turn of
the century. When that method was applied, it confirmed the order of events
as established by the relative dating techniques long in use.

The major point here is that evolutionary theory is absent from the entire
account above. Evolution provided an explanation for the order of fossils
in the geological strata and their geographic distribution already
determined by other methods.

The best, most concise, discussion of this history of which I am aware is
the book "The Meaning of Fossils" by Martin J.S. Rudwick (Univ. of Chicago
Press,1985).

Keith

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Received on Mon Oct 12 12:43:53 2009