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Fossil Dating
HOW DO WE
KNOW THE
AGE OF
FOSSILS?
-Scientists use 2
methods to
determine the age of
fossils:
1. Relative Dating
2. Absolute Dating
Relative Dating
Shows the order in which fossils
occurred- does not give exact ages.
 Shows what organisms lived together.
 Scientists look at where fossils are
located within the rock column.
 Use the Law of Superposition

Law of Superposition
Sedimentary layers are deposited in a
time sequence
 Oldest rock on the bottom, youngest at
the top

Youngest
Oldest
Absolute Dating
Determines the specific age of a fossil
 Looks at chemical properties
 2 types:

◦ Carbon-14 (radiocarbon)
◦ Potassium-Argon
Carbon-14 Dating
Also known as Radiocarbon dating
 Used to date organic substances
 Scientists measure the radiocarbon in the
fossil to determine its age
 Can only date specimens up to about
60,000 years old

Potassium-Argon Dating
Scientists determine the age of the rock
surrounding the fossil to determine the
fossil’s age.
 Used only for inorganic substances (rocks
and minerals)
 Scientists measure the amount of argon in
the rock to determine its age
 Dates rock 60,000 years old and older

QUIZ
Which rock layer is the
oldest? Youngest?
Youngest
Oldest
If you wanted to figure out the exact
age of a rock, what technique would
you use?
a.Relative Dating
b.Carbon-14 Dating
c.Law of Superposition
d.Potassium-Argon Dating
If you were looking to find the
exact age of a fossil that is at least 1
million years old, what technique
would you use?
a. Carbon-14 Dating
b. Potassium-Argon Dating
c. Relative Dating
d.You can’t; it is impossible
If you wanted to figure out the
exact age of a fossil that is less than
40,000 years old, what technique
would you use?
a. Carbon-14 Dating
b. Potassium-Argon Dating
c. Relative Dating
d.You can’t; it is impossible