# Sept.10, 2011 LEQ 4 Law of Superposition

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Sept.10, 2011 LEQ 4 Law of Superposition
Homework Due tomorrow! Words to know: relative age, absolute age, law of superposition, index fossil, intrusion Do now: Do you have brothers/sisters? If so, how old are they? Are they older or younger than you? If not, how old is your closest friend? Are they older or younger than you?

LEQ #4: What information do humans get from rock layers, index fossils, and ice cores in order to paint a picture of Earth’s History? By the end of today, SWBAT… Compare and contrast absolute and relative age Understand and apply the law of superposition to diagrams and descriptions Explain how index fossils are used to date rocks

Activating Strategy Put the following events in order:
Nuclear Bomb dropped on Hiroshima, Japan (1945) George Bush became President (2000) Pluto was no longer considered a plant (2006) The Internet was “invented” (1994) The U.S. launched the first space shuttle (1981) How did you decide to put them in order?

Look back at your words to know… relative age absolute age
What does relative mean? Think about how things relate What does absolute mean? Think about math What do you think these words mean when describing age?

T-Chart Relative Age Absolute Age
-Tells age compared to something else -Uses words like “older,” “younger,” and “same age as” -Ex: I am younger than my brother. -Tells the exact age -Uses numbers -Ex: My brother is 16.

Pair and Write! With your partner:
1.) Tell each other your absolute age 2.) Write a sentence about how old YOU are RELATIVE to your partner 3.) Discuss  What is the difference between absolute and relative age?

Scientists use rocks to figure out Earth’s History!
Ask students which rock layer is older, the one at the bottom (point) or the one at the top (point)? They should say the one at the bottom. We can see 2 BILLION years worth of Earth's geologic history in the Grand Canyon!

You just figured out the… Law of Superposition!!!

Law of Superposition The Grand Canyon
Define It In undisturbed sedimentary rock layers, -Oldest rock layers are at the bottom -Youngest rock layers are at the top Draw it Example The Grand Canyon Sentence The Law of Superposition tells us the relative age of rocks. Law of Superposition

So what is THIS???

INTRUSION!!! Magma that pushes through rock layers. Is younger than the layers it cuts across because the layers had to be there before it could cut across them!. Science says… intrusion! Science says is a hand motion game. When science says intrusion, take your hand and push it up into the air like you were magma pushing through rock.

Hot Question! If you found this fossil in your backyard, what could you infer about how your backyard looked in the past?

Absolute Dating Techniques
Index Fossils: fossils of a species that only existed during a limited time The fossil is the same age as the layer of rock it is in If there is a fossil in a rock layer, and we know what time period the animal lived, we can conclude that the rock was formed during that period. After introducing index fossils, ask students which fossils could be index fossils in this diagram (2, 5, 3). Say, well if we know that fossil 2 is 50 million years old, what do we know about the layer it is in? If we know that fossil 5 is 25 million years old, what do we know about the age of the layer it is in?

Index fossils help scientists figure out how old rock layers are!

How to find the absolute age of an index fossil…
Radioactive dating… more to come on this, but take a look at this chart… Think.Pair.Share.

Use the diagrams on your desk
Use the diagrams on your desk. With your partner, answer the question on your dry erase board. When I say “3-2-1, Boards Up,” you should hold your board in the air. If your board does not go up immediately, you will be DQ’ed for that question.

Real Life Practice  Look at the cup on Ms. K’s desk
What is the oldest rock layer? How do you know?

Real Life Practice  Look at the cup on Ms. K’s desk
What is the youngest rock layer? How do you know?

Real Life Practice  Look at the cup on Ms. K’s desk
Imagine that there is a layer of magma pushing up through all 4 “rock” layers. What is this called?

Real Life Practice  Look at the cup on Ms. K’s desk
List all rock layers in order from oldest to youngest.

Real Life Practice  Look at the cup on Ms. K’s desk
What is the name of the law that tells us this is true?

Hot Question The law of superposition states that in horizontal layers of sedimentary rock, each rock layer is ___________. a. Younger than the layer above it and older than the layer below it b. Neither older nor younger than other layers c. Older than the layer above it and younger than the layer below it d. Always older than any vertical layers