Unit A Chapter 2

Views of the Earth’s Past

Fossils

• Fossils– Traces or remains of living things

They can give us clues into the following

Climate: weather conditions

Habitat: where they lived

Food: what they ate

Appearance: what they looked like

Original Remains

• Ice-whole organisms have been found in ice

• Tar-thick oily liquid that preserves whole organisms

• Amber-Tree Sap-traps insects on trees– Think the movie Jurassic Park

T-Rex in Ice

Woolly Mammoth found in ice

Tar Pits

Tar Pit in Downtown LA

Amber-Tree Sap

Fossil Formation

• Molds and Casts– Casts

• Shape of organisms remainsMolds-shape was filled in with liquid rock and took shape

• Petrified Wood– Stone trees-sediments pour into holes in wood and

harden

• Carbon Films– Imprints on rocks of entire animals

• Trace Fossils-leave evidence – Footprints, trails, holes, and even feces left behind

Casts of Fossils

Let’s Make a Cast

• Using your play doh! and the shell. We are going to make an example of a cast

• Watch as I demonstrate.

Molds of Fossils-the casts have been filled in

Let’s Make a Mold

• Using your play doh! and the shell. We are going to make an example of a mold

• Watch as I demonstrate.

Petrified Wood

Carbon Prints-Living things leaving behind the carbon in their bodies

Let’s Make an Imprint

• Using your play doh! and the shell. We are going to make an example of an imprint

• Watch as I demonstrate.

Trace Fossils-evidence of something that was alive

Let’s Make a model of a trace fossil

• Using your play doh! and the shell. We are going to make an example of a cast

• Watch as I demonstrate.

Ice Cores

• Ice Core-Tubular sample that shows the layers of snow and ice– Vertical timeline– Ice traps air

• Contents of air like dust and ash from volcanoes• Radiation trapped• Thicker layers mean ice ages• Thin layers mean warmer temps

Ice Core Samples

Dating of Fossils

Relative Age Dating

• Age of something in relation to something else

• Get an age of one student in the 8th grade, we then guess the age of the rest of the students

• Find older brother and younger sister, guess ages based on your age

Practice Relative Age Dating

• Place all pennies without looking at the years tails side up.

• Pick one penny and flip it heads up. Using the Absolute age of that penny. Take a guess as to the Relative age of the rest.

Results: Add to your notes

• How accurate were you in guessing the relative age of the penny?

• Rearrange your pennies to get the correct order based on the age.

• What kind of things threw you off of getting your relative age?

Relative Age Dating

Relative Age of rock layers

• By studying layers of rocks we can determine the age of the layers, or least figure out which came first

Absolute Age Dating

• Absolute Age Dating-actual age of a rock or fossil

• Can help to figure out relative age of other rocks or fossils

• We find this out using half-life

Half-Life

• Half-Life-length of time it takes for atoms of a sample to decay away

• Uranium-235 can be used to determine igneous rock layers– Half-life-704 million years

• Carbon-14 can be used on fossils, carbon found in all living things– Half-life-5730 years

Half-Life Problems

• Take your pennies. They are the decaying atoms of a fossil.

• Shake them up in the bag and dump them on the desk. Take away the decayed pennies (the heads). Do this until your only have 1 penny left.

• How many half-life's did your fossil have?

Carbon-14

• Carbon-14 has a half-life of 5730 years

• Using your fossil, how old is your fossil?

• Number of half-life's times 5730.

• How old was your sample?

Law of Superposition of rock layers

• The layers on top of a rock layer are younger.

• The layers on the bottom of a rock layer are always older

• Usually!

Answer all questions on your whiteboards.

Which rock layer is the oldest? How can you tell?

A

B

Undisturbed Layers of Rock

• Normal Layers of rock that follow the law of superposition

Undisturbed Rock Layers

Angular Unconformities

• Rock layers that have been moved by a geological event

Angular Unconformities

What might have moved these layers?

Put the letters in order from youngest to oldest?

Which rock layers are the youngest? Oldest?

How did the rock layers on the bottom get turned?

A

B

C

Angular Unconformity

Which rock layer is the youngest? Which is the oldest?

A

B

C

Put the letters in order from youngest to oldest.

A

B

C

D

E

Igneous Intrusion Layers

• Rock layers that have igneous rock from the mantle push their way in

A

B

C

A

B

C

D

Index Fossils

• Fossil with the layers that can give us clues to the age of the rock layers

• If I know for certain the age of the fossil, then I can find the relative age of fossils and rock layers around them

Uniformitarianism

• Uniformitarianism– Earth is always changing– Same things changing them in the past are

changing them today

Geologic Time Scale

• Divides the earths history into sections

• Just like in Soc. Studies, the earth itself has a timeline

• Turn to pg. 237 in books on desk