In order to do your best on this activity, you must understand a few of the basic principles that are applicable to relative age relationships between rocks. Help us work out the relative ages of the layers of sedimentary rocks.Numerical dating determines the actual ages of rocks through the study of radioactive decay.Relative dating cannot establish absolute age, but it can establish whether one rock is older or younger than another.
It looks as though one group of layers was tilted and eroded away before new rocks were formed on top.It sounds like common sense to you and me, but geologists have to define the Principle of Original Horizontality in order to make assumptions about the relative ages of sedimentary rocks. Say you have a layer of mud accumulating at the bottom of a lake. More sediment accumulates from the leaf litter and waste of the forest, until you have a second layer.Once we assume that all rock layers were originally horizontal, we can make another assumption: that the oldest rock layers are furthest toward the bottom, and the youngest rock layers are closest to the top. The forest layer is younger than the mud layer, right? When scientists look at sedimentary rock strata, they essentially see a timeline stretching backwards through history.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.Geologists use this type of method all the time to establish relative ages of rocks. What are two ways we can determine the age of rocks? An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Before absolute dating of rocks was developed in the 20th century, geologists had to rely on relative age dating, which places geologic events in their order of occurrence.In order to establish relative dates, geologists must make an initial assumption about the way rock strata are formed. sediments, which are deposited and compacted in one place over time.It's called the Principle of Original Horizontality, and it just means what it sounds like: that all rock layers were originally horizontal. As you can imagine, regular sediments, like sand, silt, and clay, tend to accumulate over a wide area with a generally consistent thickness.Learn how inclusions and unconformities can tell us stories about the geologic past.We'll even visit the Grand Canyon to solve the mystery of the Great Unconformity!