Watch this video to find out how we use index fossils to establish the relative ages of rocks.
In previous lessons, we talked about the Geologic Time Scale and how scientists use it to piece together the history of the earth.
Despite seeming like a relatively stable place, the Earth's surface has changed dramatically over the past 4.6 billion years.
Mountains have been built and eroded, continents and oceans have moved great distances, and the Earth has fluctuated from being extremely cold and almost completely covered with ice to being very warm and ice-free.
(a) Relative Dating This technique uses principles of stratigraphy (rock strata) and the study of fossils (palaeontology) to determine the relative ages of rocks and sediments. Field geologists' rely on a number of simple techniques for dating rocks and constructing geological successions. The Law of Strata Identified by Fossils is a little bit more complex.
One outcrop shows layers from one geologic time period, while the other outcrop represents a different time. Can he put the pieces together to make the story more complete? Let's find out how scientists deal with this common problem by using the fossils inside the rocks.
Back in 1793, there lived a land surveyor named William Smith.
The diagram right shows two distinct faunal assemblages.
What can be deduced from our two distinct faunas in terms of their usefulness in the relative dating of rocks?
We talked about relative dating of rocks and how scientists use stratigraphic succession to compare the ages of different rock layers.