1. Do Now:
Absolute Age Radioactive Dating
Relative Age Index Fossil
1. _______________________ organism that lived for only a short time
which can be used to tell the age of the rock layer it exists in
2. _______________________ a technique used by scientists to
determine the absolute age of objects
3. _____________________________ the age of an object or event
described in comparison to other objects or events
4. _________________________ Example: The Earth is younger than the
5. _______________________ Test used by scientists to find the exact
age of rocks and fossils
6. _______________________ Found in rock layers and allow scientists to
determine the relative age of the rocks
3. Rock Layers
Sedimentary rocks are formed when
sediments are cemented together by heat and
pressure to form rocks
This conversion of sediments into rock
happens after the sediments are buried by
new sediments. Sedimentary rocks form in
6. Rock Layers
When the sedimentary rock buried deep enough
they undergo more heat and pressure to
become different kinds of rock.
Quick Review: if sedimentary rocks undergo heat
and pressure to become a new type of rock, what
type of rock is it now??
8. Law of Superposition
The Law of Superposition states
that each undisturbed layer of
sedimentary rock is older than a
layer above it.
9. Law of Superposition
The bottom layer of rock forms first, which means that
it is the oldest
Each layer above that is younger than the one below
and the top layer is the youngest of all.
This ordering is a type of relative dating because you
can’t be sure when each layer was formed, so you
know the layer’s age in relation to the other layers
15. Igneous Intrusion
Here molten rock forces its way up through
sedimentary layers. Because the sedimentary rock
have to be present before the molten rock can cut
through, the igneous rock must be younger than the
layers it cuts through.
The molten rock can erupt and flow to the surface of
the earth and form its own layer of igneous rock on
top of the sedimentary rock
If there is an unconformity, then the
youngest layer may not be on top.
Scientists can determine the original order
by comparing the disturbed rock layers with
a similar stack of undisturbed rock layers.
28. Exit Ticket
1. Which statement is true?
A. The oldest layers of rock and soil are closest to the surface of
B. The youngest layers of rock and soil are farther away from
the surface of the earth.
C. Carbon-14 dating is an example of relative dating, and the
law of superposition is an example of absolute dating.
D. Absolute geologic dating and relative geologic dating are two
methods used by scientists to determine the age of geologic
2. Which is a process that allows scientists to compare rock
layers with others in a sequence to determine their age?
A. radiometric dating
B. absolute dating
C. relative dating