Relative age dating of rocks

Your goal is to study the smooth, parallel layers of rock to learn how the land built up over geologic time.

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Geologists find the cross-cutting principle especially useful for establishing the relative ages of faults and igneous intrusions in sedimentary rocks.Sometimes, geologists find strange things inside the strata, like chunks of metamorphic or igneous rock.Discover how geologists study the layers in sedimentary rock to establish relative age.Learn how inclusions and unconformities can tell us stories about the geologic past.Let's say we find out, through numerical dating, that the rock layer shown above is 70 million years old.

We're not so sure about the next layer down, but the one below it is 100 million years old. Not exactly, but we do know that it's somewhere between 70 and 100 million years old.Relative dating cannot establish absolute age, but it can establish whether one rock is older or younger than another.Relative dating requires an extensive knowledge of stratigraphic succession, a fancy term for the way rock strata are built up and changed by geologic processes.These items are called inclusions - foreign bodies of rock or mineral enclosed within another rock.Because the sedimentary rock had to have formed around the object for it to be encased within the layers, geologists can establish relative dates between the inclusions and the surrounding rock.Let's say, in this set of rock strata, that we found a single intrusion of igneous rock punching through the sedimentary layers.