More on Law of Superposition

Science Starter

• What type of equation is the following?

2C₈H₁₈ + 25O₂ —> 16CO₂ + 18H₂O

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2.) Is this equation balanced? Show your work (count the atoms)

EQ: How do scientists determine the age of rock layers?

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8.E.2 Understand the history of Earth and its life forms based on evidence of change recorded in fossil records and landforms.

8.E.2.1 Infer the age of Earth and relative age of rocks and fossils from index fossils and ordering of rocks layers (relative dating and radioactive dating)

8.E.2.2 Explain the use of fossils, ice cores, composition of sedimentary rocks, faults, and igneous rock formations found in rock layers as evidence of the history of the Earth and its changing life forms

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Learning Objectives

• SWBAT correlate rock layers.
• SWBAT apply the law of superposition to determine relative age.
• SWBAT name the forces that affect layering of rocks.

Review: Law of Superposition

• So, the relative age of the rock is older if farther down in the rock layer
• It is younger if it is closer to the top
• This is called the Law of Superposition, which states “each rock layer is older than the one above it”

Scientists can use index fossils to show that rocks or geologic events occurring at different locations are the same age. This process is known as Correlation

Law Of Superposition

and Correlation activity

1.) Cut out the FOUR rock layer strips A-D.

• MAKE SURE TO KEEP THE NUMBERS and letters!

2.) Correlate the layers and put the strips side by

side.

a.) Look for similar patterns and index fossils!

3.) Once done, wait for further instructions!

Law Of Superposition

and Correlation activity

• What number is the oldest?
• What number is the youngest?
• What number(s) have NO index fossils?
• Which numbers are in the layer that has the most abundant index fossil?

6

1

1, 5, 6, 9,11

3, 8, 10

Original Horizontality

• Sediment goes down in horizontal layers.
• The Law of Superposition is true only if the rock layers stay in order
• If layers are turned

sideways then there

has been an earth-

quake.

Cross-Cutting Principle:

• When something cuts across a body of rock, that “something” is younger than the rock it cuts across.

Lava/Magma Earthquake

(intrusion) (fault)

Intrusion

Lava cuts/melts through rock layers in Earth’s crust.

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Which is older

C or B?

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What are the

characteristics of

an intrusion in

a rock layer?

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C

Laws of Geologic History

• Superposition—Oldest rocks on the bottom of an undisturbed sequence of rock
• Original Horizontality—Sedimentary are initially deposited in flat (horizontal) layers
• Cross-cutting Relationships—Objects which cross-cut rocks are younger than the rocks themselves (ex: fault or intrusion)

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• Faults are cracks caused by plate movement
• Intrusions are lava that melted through rock and then hardened

Which is older:

F or S

How do you know?

Superposition Challenge Practice

Exit Ticket

• Name the YOUNGEST layer.
• Name the OLDEST layer.
• Name the FAULT.
• What is D called?
• T/F: Intrusions from magma are younger than than the surrounding rock.