Fossil DatingFossil Dating

HOW DO WE HOW DO WE KNOW THE KNOW THE AGE OF AGE OF FOSSILS?FOSSILS?

-Scientists use 2 methods to determine the age of fossils:

1. Relative Dating 2. Absolute Dating

Relative DatingRelative DatingShows 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 SuperpositionLaw of SuperpositionSedimentary layers are deposited

in a time sequenceOldest rock on the bottom,

youngest at the topYoungest

Oldest

Absolute DatingAbsolute DatingDetermines the specific age of a

fossilLooks at chemical properties2 types:

◦Carbon-14 (radiocarbon)◦Potassium-Argon

Carbon-14 DatingCarbon-14 DatingAlso known as Radiocarbon

datingUsed to date organic substancesScientists measure the

radiocarbon in the fossil to determine its age

Can only date specimens up to about 60,000 years old

Potassium-Argon DatingPotassium-Argon DatingScientists 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

QUIZQUIZ

Which rock layer is the oldest? Youngest?

Oldest

Youngest

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