Isotope dating method
Let us imagine that the date reported by the lab was 150.7 ± 2.8 million years.
Our geologist would be very happy with this result.
On his return, he sends his sample to the laboratory for dating, and after a few weeks receives the lab report.From his research, our evolutionary geologist may have discovered that other geologists believe that Sedimentary Rocks A are 200 million years old and Sedimentary Rocks B are 30 million years old.Thus, he already ‘knows’ that the igneous dyke must be younger than 200 million years and older than 30 million years.He may suggest that some other very old material had contaminated the lava as it passed through the earth.Or he may suggest that the result was due to a characteristic of the lava—that the dyke had inherited an old ‘age’. 200.4 ± 3.2 million years) implies that the calculated date of 200.4 million years is accurate to plus or minus 3.2 million years.
In fact, he would have been equally happy with any date a bit less than 200 million years or a bit more than 30 million years.