To establish the age of a rock or a fossil, researchers use some type of clock to determine the date it was formed. Geologists commonly use radiometric dating methods, based on the natural radioactive decay of certain elements such as potassium and carbon, as reliable clocks to date ancient events.

How can you tell the age of layers?

To date rock layers, geologists first give a relative age to a layer of rock at one location and then give the same age to matching layers at other locations. Certain fossils, called index fossils, help geologists match rock layers.

What are the 2 different ways to determine the age of a rock?

​There are two main ways to determine the age of a rock, these are Relative dating and Absolute dating. Relative dating is used to determine the relative order of past events by comparing the age of one object to another.

How do you determine rock layers from youngest to oldest?

The principle of superposition states that the oldest sedimentary rock units are at the bottom, and the youngest are at the top. Based on this, layer C is oldest, followed by B and A.

How can we tell which layers of fossils are older than others?

To get an age in years, we use radiometric dating of the rocks. Not every rock can be dated this way, but volcanic ash deposits are among those that can be dated. The position of the fossils above or below a dated ash layer allows us to work out their ages. The volcanic ash layer is dated as 507 million years old.

What are the 3 types of intrusive rock?

Igneous intrusions form when magma cools and solidifies before it reaches the surface. Three common types of intrusion are sills, dykes, and batholiths (see image below).