The field relationships are generally broad, and a wide range of ‘dates’ can be interpreted as the time when the lava solidified.What would our geologist have thought if the date from the lab had been greater than 200 million years, say 350.5 ± 4.3 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.
For example, a geologist may examine a cutting where the rocks appear as shown in Figure 1.
Here he can see that some curved sedimentary rocks have been cut vertically by a sheet of volcanic rock called a dyke.
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.by Tas Walker A geologist works out the relative age of a rock by carefully studying where the rock is found in the field.The field relationships, as they are called, are of primary importance and all radiometric dates are evaluated against them.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.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.