Unit 2 Lesson 1 Age of Earth's Rocks

Unit 2 Lesson 1 Age of Earth's Rocks

Target: I will be able to explain how scientists determine the ages of Earth's rocks and fossils.

Relative Dating - Rock Layers

Mudstone, shale, and limestone are examples of sedimentary rock likely to contain fossils. As the layers of sediment build up on top of one another, they create a physical timeline.

Why Are Fossils Only Found in Sedimentary Rock?

Sedimentary rocks are the one type which can contain fossils because these rocks are formed on the Earth surface, under the water, at very low temperatures and pressures. In other words, the biosphere can only interact with the sediments.

Multiple Choice

Which rock layer is older? The rock layer that contains the ammonites or the trilobites?

• ammonites

• trilobites

Watch Brain Pop - Relative Dating

Then come back and we will answer some questions.

Multiple Choice

Strata are mostly found:

• underground

• on Earth's surface

• in oceans

• in the atmosphere

Multiple Choice

According to the principle of superposition, younger strata form _____ older strata.

• below

• above

• around

• next o

Multiple Choice

Scientists currently estimate that Earth is approximately ____ years old.

• 600 years old

• 4.5 million years

• 4.5 billion years

• 53 million years

Multiple Choice

What is most likely true of all the strata from the Jurassic Period?

• They contain rock from the Jura Mountains

• it is more than 1 billion years old

• they contain similar fossils

• they do not contain sedimentary rock

What is Relative Dating?

Relative Dating - 

 A method of determining the age of a fossil by comparing its placement with that of fossils in other layers of rock.

Law of Superposition

in horizontal sedimentary rock layers, the oldest layer is at the bottom. Each higher layer is younger than the layers below it. Notice these rock layers are not disturbed, meaning they were not interrupted by magma or other rock deformity.

Multiple Choice

In the stack of pancakes, where are the newest pancakes?

• on the bottom

• in the middle

• on the top

Rock Layers with Unconformities

Unconformities occur when either erosion wears away rocks, or rock deposits never form. Therefore, a time gap exists between when the rocks below the unconformity formed and when those above it formed. ... Common to all three, erosion causes them to form, and younger rocks sit on older rocks.

Multiple Choice

An unconformity can happen because deposition has been stopped which causes a gap in the rock layers.

• true

• false

Crosscutting Law

If a fault or other body of rock cuts through another body of rock then it must be younger in age than the rock through which it cuts and displaces.

Multiple Choice

What letter represents the most recent even?

• A

• B

• C

• D

Law of Inclusion

The magma that has risen up into the surrounding rock layers will be younger than the rock layers.

Intrusion of Rock Layers

 An intrusion is always younger than the rock layers around and beneath it.

Multiple Choice

Which letter represents the most recent event?

• A

• B

• C

• D

Multiple Choice

Which letter represents the most recent event in the rock layer puzzle?

• 1

• 2

• 3

• 4

Index Fossils

Are fossils used to define and identify geologic periods. The best index fossils are common, easy-to-identify at species level, and have a broad distribution

Multiple Choice

Ammonites and trilobites are good examples of Index fossils.

• true

• false