Chapter 9, Section 1: Relative Dating
Ahhh! I’m not
dating HER ! She’s
my cousin!
Eewww!
No way!
9.1 The beginnings of geology
• In 1666, Nicholas
Steno, a Danish
anatomist, studied a
shark’s head and
noticed that the
shark’s teeth
resembled mysterious
stones called
“tonguestones”.
9.1 Evidence from Rock
• Steno theorized that
tonguestones
looked like shark’s
teeth because they
actually were
shark’s teeth that
had been buried
and became fossils.
What is 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.
Use relative dating to determine which event – the foot step,
the tire track, or the snow fall - happened first.
The Present Explains the Past
• James Hutton (1726–
1797) showed how
processes today might
explain what happened
a long time ago.
• For example, when it
rains really hard you
might see flowing water
washing away
sediment. When the
rain stops, you might
see grooves left behind
by the flowing water.
Superposition
• Steno’s ideas for
relative dating include
superposition, original
horizontality, and
lateral continuity.
• Superposition states
that the bottom layer
of sedimentary rock is
older than the layer
on top because the
bottom layer formed
first.
A stack of newspapers illustrates
superposition. The oldest
newspaper is on the bottom of
the stack and the more recent
newspapers are piled on, with
the most recent on top.
The Fossil Record
The fossil record is the ordering of fossils
throughout geological time in layers of rock
that accumulate and form.
Faunal Succession
• Faunal succession uses
fossils to identify the
relative age of the
layers of a rock
formation.
• The organisms found in
the top layers appeared
after the organisms
found in the layers
below them.
Use the illustration (above) to answer the
following questions: Did human beings
live at the same time as the dinosaurs?
Did dinosaurs roam the earth at the
same time as trilobites?
Fossils and Earth’s changing surface
• Most of the land
on Earth was part
of a large
landmass, called
Pangaea, about
250 million years
ago.
● Fossils provide evidence for how
Earth’s surface has changed over time.
● Scientists map fossil locations.
● Understanding Earth’s past helps
explain how similar plants and animals
ended up in different locations.
Huh?
Did you know….
that shark teeth are common fossils in Georgia and are
the official state fossil? From the Cretaceous to the
Miocene periods (approximately 10 to 70 million years
ago) sharks hunted and stalked the coastal areas of
Georgia. It is very rare to find a fossil of an actual
carcass of these prehistoric sharks, but their teeth are
found in sizable numbers due to the fact that sharks
constantly lose and replace their teeth.