RELATIVE DATING

WHAT IS IT?

Determining whether an object is younger or older than the objects around it

DEPOSITION OF SEDIMENTARY ROCK

• Deposited in horizontal layers
• Younger layers on top of older layers

LAW OF SUPERPOSITION

Younger rocks are above older rocks if left undisturbed

UNCONFORMITIES

• When sediment is eroded
• Sediment is not deposited for a long time

CROSSCUTTING RELATIONSHIPS

A fault or a body of rock is younger than the rock that it cuts through.

FOSSILS

• Traces or remains of an organism that lived long ago
• Organisms evolved over time.
• Lived in a specific time zone.
• Can be used to find the relative date of rocks around it.

GEOLOGIC COLUMN

An ordered arrangement of rock layers based on the relative ages of rocks, with the oldest at the bottom.

HOW THEY ARE USED

• Scientists can piece together layers to their relative location

ABSOLUTE DATING

WHAT IS IT?

• Finding the actual age of an object

RADIOACTIVE DECAY

The breakdown of a radioactive isotope to a stable one.

HALF LIVES

They decay at a constant rate. It decays in units of time.

RADIOMETRIC DATING

Finding the absolute age of a sample by comparing the parent isotopes to the daughter isotopes

RADIOCARBON DATING

• Measures carbon-14 to carbon-12
• Only used for organic matter
• Lived in the last 45,000 years

POTASSIUM-ARGON DATING

• Measures potassium-40 to argon
• Used to date igneous rocks
• Used to date rocks between 100,000 to a few billion years old

URANIUM-LEAD DATING

• Radioactive isotope that decays to lead-206
• Determine the age of igneous rocks between 100 million
• and billions of years old.
• Used to find the age of Earth.

EARTH'S AGE

• 4.6 billion years old
• Scientists did radiometric dating on meteorites.

INDEX FOSSILS

• Had to live in a short definite period of time
• Relatively common
• Found over a large area
• Features that makes them different from other fossils

HOW INDEX FOSSILS WORK

• Can be used to estimate the age of rock layers
• Gives a range of ages
• Can be used to date other rock layers.