Ageing Fossils

Ageing Fossils

Mr. Reece

8th Grade Science

Speight Middle School

The Fossil Record

• Millions of fossils have been collected and studied

• Gives important information about past life and environments on Earth

• Is considered incomplete because fossilization is very rare

Fossil Record Evidence

• Certain fossilized organisms could only live in specific environments or climate conditions

• Extinction of lifeforms as well as how and when new life-forms appeared

• Shows how organisms have evolved

Multiple Choice

The millions of fossils that scientists have collected are called...

• The Geologic Time Scale

• The Fossil Record

• The Origin of Species

• A really neat fossil collection

Multiple Choice

Which of the following can be learned by using the fossil record?

• When organisms changed or evolved

• When organisms appeared on Earth

• When organisms became extinct

• All the above

Multiple Choice

The formation of any fossil is a common event.

• True

• False

Relative Age

• Means the age of one object compared to the age of another object

• Does not tell the exact age of an object

• Can be determined using two basic methods: the ordering of rock layers and index fossils

Law of Superposition

• Used to read rock layers

• States that each rock layer is older than the one above it

• Using this, scientists infer that the relative age of the rock or fossil in the rock is older if farther down in the rock layers

• Best used when the rock layers have been preserved in their original sequence

Law of Superposition

• Over millions of years, tectonic plate motion can distort these layers

• As a result of this, the youngest layers of rock are not always found on top, because of the folding, breaking, and uplift of layers

Multiple Choice

In layers of sedimentary rock, the _________ layer is usually at the bottom. Each higher layer is _________ than the layers below it.

• oldest, younger

• youngest, older

• youngest, younger

• oldest, older

Multiple Choice

Which of the following orders the rock layers accurately from youngest to oldest?

• 1, 2, 3, 4, 5

• 2, 3, 4, 5, 1

• 5, 4, 3, 2, 1

• 1, 2, 3, 5, 4

Multiple Choice

Which fossil is relatively the oldest?

• Trilobite

• Crinoid

• Ammonite

• Gastropod

Multiple Choice

Which of the following correctly lists the layers in order from oldest to youngest?

• A, B, C, D, E

• E, D, C, B, A

• C, B, A, D, E

• E, B, C, D, A

Index Fossils

• Certain fossils used to help find the relative age of rock layers

• Characteristics:

• 1. Widespread in rock layers

• 2. Short-lived

• 3. Abundant

• 4. Be unique

Index Fossil Example

• The shorter time period a species lived, the better an index it is

• Trilobites: Group of hard-shelled animals whose body had 3 sections, lived in shallow seas, and became extinct about 245 mya

• If a trilobite is found in a certain rock layer, it can be compared with trilobites from other layers to estimate the age of the layer it was found in

Multiple Choice

What is the best reason that fossil #4 is NOT a good index fossil?

• It is not widespread

• it is not short-lived (in numerous layers)

• It is in half of the outcrops

Multiple Choice

The best index fossils have which two traits?

• widespread geographically, long lifespan

• specific place, long lifespan

• widespread geographically, short lifespan

• specific place, short lifespan

Radiometric Dating

• Used to estimate how long ago rocks formed and to infer the ages of fossils contained within those rocks

• Also known as absolute dating

• Over time, radioactive “parent atoms” decay into stable “daughter atoms”

Radiometric Dating Process

• When molten rock cools (igneous rock), radioactive atoms are trapped inside and decay at a predictable rate

• Scientists can estimate the amount of time that has passed since that rock formed by measuring the number of unstable atoms left in the rock

• Example: Carbon-14 Dating

Multiple Choice

Scientists use radioactive decay to measure...

• relative time

• half-lives

• absolute time

• time of day

Multiple Choice

How does absolute age differ from relative age?

• only absolute dating indicates which rock is older than another

• only absolute dating finds the age in years

• only relative dating finds the age in years

Use of Artifacts

• A variety of artifacts are used to determine the Earth and how its life forms have changed over time

• Two Important Artifact Pieces:

• Sedimentary Rock

• Ice Cores

Ice Cores

• Cylinders of ice that are drilled out of glaciers and polar ice sheets

• Play an important role in helping scientists to gain knowledge of how Earth’s climate has changed over time

• Snow carries with it the compounds that are in the air at the same time

Ice Core Importance

• Air compounds build up layer upon layer of compacted snow which becomes ice

• Within these ice layers, there is a record of the atmosphere at the time that the snow creating the ice layers fell

Sedimentary Rocks

• Makes up about 75% of the rocks on the Earth’s surface

• Form on the surface of the Earth, anywhere that sand, mud, or other types of sediment collect

• Gain knowledge of Earth’s climate, life, and geologic history

Rock Disturbances

• Can be disturbed by igneous rock

• Happens when molten rock forces its way up through layers above it

• Sedimentary rock layers must be there first

• Sometimes molten rock will force its way to the surface and erupt, creating a younger igneous layer at the surface