Transcript Relative Dating

Fossils and Dating
8-2 notes
What you will learn:
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The rock cycle includes the formation of new
sediment and rocks and that rocks are often
found in layers, with the oldest generally on
the bottom.
Radiometric dating can be used to determine
how old a rock is and the how old the fossils
in the rock are.
The Principle of Superposition.
Imagine that you find this in your
back yard while digging…..
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This is not very likely,
but someone had to
be the first person to
dig up a T-rex.
How did they explain
what it was?
How could they
determine how old
the bones were?
What is relative dating?
Compares one rock layer with others in a
sequence.
 Determining if an object/event is older or
younger than another object or event.
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This method of dating does not give a # or tell
how many years old an object/event is.
Principle of Superposition
 Younger
rocks are on top of
older rocks in undisturbed
layers.
 Fossils found in younger layers
must be younger than fossils
found in older, lower layers.
Rock Layers
What that looks like in real life…
Not all rocks lay undisturbed…
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Look at the pictures on page 241.
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How did the rocks get that way?
Erosion, folding, tilting, faults, and intrusions,
are all caused by weathering, plate movement,
and magma from below the plates being forced
up.
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Disturbing the rock layers
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Folding is the bending of
rock layers from stress
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Tilting happens when the
Earth’s forces make the
rocks slanted
Gaps in the records - Unconformities
 Sometimes
rock layers are missing.
 Never formed
 Or washed away by weathering
Fossils
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A trace or remain of an organism that lived long
ago.
Fossils are mostly found in Sedimentary rock.
There are fossils of freshwater (lake) organisms
in Antarctica. What does that tell us about
Antarctica?
It used to be much warmer.
Trace Fossils are traces that organisms leave
behind – like footprints or scat.
Absolute Dating
A Method of dating rocks by using radioactive
isotopes.
Through the absolute dating of meteorites scientist
determined that the Earth is 4.6 Billion years
old.
In one half-life the amount of radioactive material
decreases by one-half.
Fossils and Dating
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Relative dating and Absolute dating of rocks can
tell you how long ago a certain fossil was alive.
What you have learned
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The layering (order) of rocks will tell you which
layers are older than other layers. (Law of
Superposition).
Relative dating compares 2 items or events to
see which one is older.
Absolute dating uses radioactive decay of certain
elements to determine how old rocks are.
What to do next:
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Write a 6 sentence summary:
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Opening or topic sentence
Detail
Detail
Detail
Detail
Closing about why the information is important.