Clearly, Sedimentary Rocks A were deposited and deformed before the Volcanic Dyke intruded them.These were then eroded and Sedimentary Rocks B were deposited.But really, how do scientists figure out how old their dinosaur bones are?And, what about other findings like fossil fish, plants and insects?It is clear that the sedimentary rock was deposited and folded before the dyke was squeezed into place.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.Knowing when a dinosaur or other animal lived is important because it helps us place them on the evolutionary family tree.
His geological cross-section may look something like Figure 2.
Instead, other methods are used to work out a fossil’s age.
These include radiometric dating of volcanic layers above or below the fossils or by comparisons to similar rocks and fossils of known ages.
The work of geologists is to tell the true story of Earth's history—more precisely, a story of Earth's history that is ever more true.
A hundred years ago, we had little idea of the story's length—we had no good yardstick for time.