So, often layers of volcanic rocks above and below the layers containing fossils can be dated to provide a date range for the fossil containing rocks. The atoms in some chemical elements have different forms, called isotopes. These isotopes break down at a constant rate over time through radioactive decay.

How can fossils be dated?

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.

Why are igneous rocks best for dating?

Scientists date igneous rock using elements that are slow to decay, such as uranium and potassium. By dating these surrounding layers, they can figure out the youngest and oldest that the fossil might be; this is known as bracketing the age of the sedimentary layer in which the fossils occur.

Is igneous intrusion is older or younger than layers A and B?

There, the magma cools and hardens into a mass of igneous rock called an intrusion. An intrusion is always younger than the rock layers around and beneath it.

Is fault l older or younger than rock layer D?

The principle of cross-cutting relationships states that a fault or intrusion is younger than the rocks that it cuts through. The fault cuts through all three sedimentary rock layers (A, B, and C) and also the intrusion (D). So the fault must be the youngest feature.

Is rock layer 1 older or younger than layer H?

First, we know from the principle of superposition that rock layer F is older than E, E is older than D, D is older than C, and C is older than B. Second, we observe that rock layer H (which is an igneous intrusion) cuts into rock layers B-F. It is therefore younger than B-F.

Which rock layer is older than layer H?

*The Law of Superposition is that an undeformed sedimentary rock layer is older than the layers about it and younger than the layers below it. According to the Law of Superposition, layer 1 was the first layer deposited, and thus the oldest layer.