7th Grade Science Student ebook

12.1 Evidence from Rocks.

CHAPTER 12: EARTH AND LIFE HISTORY

Relative dating

Relative dating Steno’s principles are used by geologists to determine the age of

fossils and rocks in a process called relative dating. Relative dating

is a method of sequencing events in the order they happened.

What is relative

dating?

Figure 12.5 shows an example of relative dating. When you use

relative dating, you are not trying to determine the exact age of an

object. Instead, you use clues to sequence the order of events that

occurred around it. Then you determine the age of the object

relative to the other objects or events in the sequence. Can you list

the three events shown in Figure12.5 in order of occurrence?

Using relative

dating to

sequence fossils

Paleontologists use relative dating to determine the sequence of

fossils in the order that each species existed. A paleontologist is

a scientist who studies fossils. A cross section of sedimentary rock

has many different layers. The oldest layers are found at the

bottom and the newest at the top. Suppose fossils were found in the

layers shown below. A paleontologist could sequence the organisms

found according to their location in the layers. The organisms found

in the top layers appeared after the organisms found in the layers

below them.

Figure 12.5: This graphic illustrates

three events: a footstep, a tire track, and

snowfall. Which event happened first?

Sequencing these events in the correct

order is a form of relative dating.

relative dating - a method of

sequencing events in the order in

which they happened.

paleontologist - a scientist who

studies fossils.