Scientists also use direct evidence from observations of the rock layers themselves to help determine the relative age of rock layers.
Specific rock formations are indicative of a particular type of environment existing when the rock was being formed.
*Life Science: Fossils indicate that many organisms that lived long ago are extinct.
Extinction of species is common; most of the species that have lived on the earth no longer exist.
INTRODUCTION Scientists have good evidence that the earth is very old, approximately four and one-half billion years old.
Scientific measurements such as radiometric dating use the natural radioactivity of certain elements found in rocks to help determine their age.
If certain fossils are typically found only in a particular rock unit and are found in many places worldwide, they may be useful as index or guide fossils in determining the age of undated strata.
By using this information from rock formations in various parts of the world and correlating the studies, scientists have been able to establish the geologic time scale.
On a larger scale, even between continents, fossil evidence can help in correlating rock layers.Sequencing the rock layers will show students how paleontologists use fossils to give relative dates to rock strata.Once students begin to grasp "relative" dating, they can extend their knowledge of geologic time by exploring radiometric dating and developing a timeline of Earth's history.Time factors of millions and billions of years is difficult even for adults to comprehend.However, "relative" dating or time can be an easy concept for students to learn.The fossils represented by the letters on this card are "younger" than the "T" or "C" fossils on the "TC" card which represents fossils in the oldest rock layer.