Geologic Dating - Red Hook Central School District

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Geologic

Time

GEOLOGIC

TIME

FOSSILS CAN ONLY BE

FOUND IN sedimentary

ROCKS.

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

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

Is “H” an intrusion or extrusion?

How can you tell?

H is an intrusion.

Contact metamorphism on top

What is an unconformity?

a buried erosional surface

How does it complicate the relative dating of rock layers?

a part of the rock record is missing

A RECORD OF UPLIFT, EROSION,

AND DEPOSITION

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.

Evolution

Explain the theory of evolution.

organisms adapt to their environment in order to survive

Evolution

Explain how the fossil record supports this theory can see that different organisms have changed over time

ABSOLUTE DATING WITH RADIOACTIVE ISOTOPES

Half-Life

 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

EXAMPLE

RADIOACTIVE ISOTOPE = URANIUM,

STABLE ISOTOPE= LEAD

(IN OTHER WORDS, URANIUM TURNS INTO LEAD)

HALF-LIFE TIPS

Radioactive Isotope

Carbon-14

Potassium

Uranium-238

Rubidium-87

Circumstance to Use

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

For rocks more than 70,000 years in age

Relatively middle-aged rocks

A rock of ancient origin

DATING WITH RADIOACTIVITY

Dating with Carbon-14

 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 C 14 , how many grams of

C 14 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 10 3 ) =1.71 x 10 4

= 17,100 years

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