GEOLOGIC TIME

Geologic TimeGeologic Time

FOSSILS CAN ONLY BE FOUND IN

ROCKS. sedimentary

WHY IS THIS STATEMENT FALSE: “THE CAVEMAN HAD

DINOSAUR FOR BREAKFAST.”?

Man and Dinosaur never lived at the same time

FAULTS ARE ALWAYS (OLDER, YOUNGER) THAN THE ROCKS THEY CUT THROUGH.

Which is older:

F or S

How do you know?

IF A GEOLOGIST FINDS AN IGNEOUS LAYER, HOW CAN SHE DETERMINE IF THE LAYER IS AN INTRUSION OR AN EXTRUSION?

INTRUSIONS

contact metamorphism on all sides

contact metamorphism on all sides

CONTACT METAMORPHISM

Contact metamorphism: occurs at the border where magma touches solid rock- at this boundary, the rock is turned into metamorphic rock through contact with the heat of the magma.

Use the ESRT to determine the type of sedimentary rock, then the metamorphic rock table to determine what the sedimentary rock turns in to at this contact boundary

EXTRUSIONS

no contact metamorphism on top

no contact metamorphism on top

Is “H” an intrusion or extrusion?

How can you tell?

Is “H” an intrusion or extrusion?

How can you tell?

H is an intrusion.Contact

metamorphism on top

H is an intrusion.Contact

metamorphism on top

What is an unconformity? What is an unconformity? a buried erosional surface

a part of the rock record

is missing

a part of the rock record

is missing

How does it complicate the relative dating of rock layers?

How does it complicate the relative dating of rock layers?

A RECORD OF UPLIFT, EROSION, AND DEPOSITION

What processes could lead to an unconformity? What processes could lead to an unconformity?

weathering and erosion

Using the diagram to the left, identify where the unconformity is located by drawing an arrow and writing the word “unconformity” next to it.

EvolutionEvolution Explain the theory of

evolution. organisms adapt to their environment

in order to survive

organisms adapt to their environment

in order to survive

EvolutionEvolutionExplain how the fossil record supports this theoryExplain how the fossil record supports this theory

can see that different organisms have

changed over time

can see that different organisms have

changed over time

Half-Life

ABSOLUTE DATING WITH RADIOACTIVE ISOTOPES

A half-life is the amount of time necessary for one-half of a radioactive, unstable substance to become not radioactive, stable.

Half life depends on the element that is unstable- some radioactive isotopes stabilize quickly, some take much longer

RADIOACTIVE ISOTOPES FREQUENTLY USED IN RADIOMETRIC DATING

EXAMPLERADIOACTIVE ISOTOPE = URANIUM, STABLE ISOTOPE= LEAD (IN OTHER WORDS, URANIUM TURNS INTO LEAD)

HALF-LIFE TIPS

Radioactive Isotope Circumstance to Use

Carbon-14 Anything organic or of relatively recent origin- Use if a fossil of any kind is mentioned in a question!

Potassium For rocks more than 70,000 years in age

Uranium-238 Relatively middle-aged rocks

Rubidium-87 A rock of ancient origin

Dating with Carbon-14

DATING WITH RADIOACTIVITY

When an organism dies, the amount of carbon-14 it contains decreases at a predictable rate

By comparing the ratio of carbon-14 to Nitrogen-14 in a sample, absolute age can be determined.

What can be done to change the half-life of a radioactive isotope?

Why is this important?

NOTHING!it is reliable to calculate age

If there is a 100g sample of C14, how many grams of C14 would remain after three half-lives?

How long would this take? Show all work.

100g 50g 25g 12.5g

3 half-lives x (5.7 x 103) =1.71 x 104 = 17,100 years