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.It relates only to the accuracy of the measuring equipment in the laboratory.Even different samples of rock collected from the same outcrop would give a larger scatter of results. He would again say that the calculated age did not represent the time when the rock solidified.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.
By looking at other outcrops in the area, our geologist is able to draw a geological map which records how the rocks are related to each other in the field.
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.
They would all have fitted nicely into the field relationships that he had observed and his interpretation of them.
He would say that the date represents the time when the volcanic lava solidified.
Such an interpretation fits nicely into the range of what he already believes the age to be.