Final answer:
Geologists can determine the same age of two rock layers using relative dating, which is based on the principle of superposition. If two rock layers have the same type of fossils and are found in the same order, they can be assumed to be the same age. Radiometric dating is another method that allows geologists to determine the exact age of rock layers.
Step-by-step explanation:
Geologists can tell that two rock layers are the same age by using a method called relative dating. This method is based on the principle of superposition, which states that in undisturbed rock layers, the oldest rocks are at the bottom and the youngest are at the top. So, if two rock layers have the same type of fossils and are found in the same order, they can be assumed to be the same age.
For example, let's say there are two rock layers, A and B. Rock layer A is found below rock layer B and contains fossils of dinosaurs. Rock layer B is found above rock layer A and also contains fossils of dinosaurs. Based on the principle of superposition, we can determine that both rock layers are the same age because they have the same type of fossils and are found in the same order.
Another method that geologists use to determine the age of rock layers is radiometric dating. This technique measures the amount of radioactive materials in each rock layer and calculates their decay rate to determine the exact age of the rocks.