Rocks Provide a Timeline
for Earth
Notes for section 4.2
First Let’s Review!
Make sure your Clickers
are on!
Index fossils are unique because
they are only found during a
specific span of time.
1. True
2. False
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Fossils can only be found in
sedimentary rock.
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2. False
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When looking at a core sample, the
oldest layer is
1.
2.
3.
4.
On the top
At the bottom
In the middle
All of the above
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Why are fossils only found in
sedimentary rock?
1.
Because heat destroys
fossils evidence
Animals only live in
areas that have
sedimentary rocks
Sedimentary rocks do
not use heat when
formed
Both 1 and 3
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3.
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What can scientists learn from core
samples?
1. Climate and other
geologic activity
2. Changes that
occurred over time
3. Life that lived during
different spans of
time
4. All of the above
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Time for Notes!!!!!
The Big Idea!
Rocks and fossils
provide a timeline for
the Earth
Watch this short video to learn
more!
Layers of sedimentary rocks show
relative age
Geologists reconstruct the past using the
relative ages of objects or events based on
clues
For example-magazine activity
Relative age is the age of an event or
object in relation to other events or objects.
Let’s take a look at this link to learn more!
http://www.ucmp.berkeley.edu/education/expl
orations/tours/geotime/gtpage3.html
Do you remember how
sedimentary rocks are
formed?
Sedimentary rocks form from things that
have been eroded and carried away to
another area (deposition)
Minerals act as glue to cement the layers
together
Over time, the sediments pile up to form
horizontal layers of sedimentary rocks
This is called the Law of Superposition
Bottom layer forms first which means it is
the oldest
So what does that tell us about the top
layer?
Index Fossils
Index fossils are:
fossils of organisms that were common
lived in many areas
existed only during specific spans of
time
This information is used to determine its
relative age and therefore the relative
age of the rock.
Radioactive Dating can show
absolute age
When we know the exact age of an object
or event, we know its absolute age
To determine the absolute age of an object
scientists must examine the elements and
see the rate at which they break down.
This is called radioactive dating or
radiometric dating
http://www.ucmp.berkeley.edu/education/ex
plorations/tours/geotime/gtpage8a.html
Did you know????
Scientists used
radiometric dating
to estimate that the
Earth is 4.6 billion
years old!
Using Absolute and Relative Age
Scientists must use all methods to
determine the age of objects and
events in order to figure out the
Earth’s past!
Radioactive dating determines the
relative age of an object.
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2. False
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Which one is NOT a characteristic
of an index fossil?
1. They are common
2. They are found in
several layers
3. Only exist during
one span of time 0% 0%
4. Can be found in
many areas
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If you tell someone that you are 12
years old, are you giving your….
1.
2.
3.
4.
Index age
Half-life
Relative age
Absolute age
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Scientists use the absolute or
relative age of a fossil to
determine the age of the rock.
1. True
2. False
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