Dating relative rock
In other words, the age should lie between 197.2 million years and 203.6 million years.
However, this error is not the real error on the date.
The field relationships, as they are called, are of primary importance and all radiometric dates are evaluated against them.
Clearly, Sedimentary Rocks A were deposited and deformed before the Volcanic Dyke intruded them.
These were then eroded and Sedimentary Rocks B were deposited.
The geologist may have found some fossils in Sedimentary Rocks A and discovered that they are similar to fossils found in some other rocks in the region.
He assumes therefore that Sedimentary Rocks A are the same age as the other rocks in the region, which have already been dated by other geologists.He would say that the date represents the time when the volcanic lava solidified.