Unit 6 Content

By STEPHEN Tressel

Unit 6 History of Earth 1-5-22

Earth's History & Fossils

8th Grade Science

Spring 2021

Multiple Choice

What are reasons for gaps in the fossil record?

• Many organisms do not have structures that can be fossilized. (There bodies are made of soft tissues instead of shells or bones)

• Some environments do not provide conditions favorable to fossil formation. (If the environment is not made from sedimentary rock we will not have fossils.)

• There are lots of fossils that we haven't found yet. (Because you need to either dig or look in mountains we are still searching for many fossils/ index fossils to help us fill the gaps of the fossil record.)

• Some geological events destroyed fossils that were in the rock layers. (Things like earthquakes and volcanic eruptions may have destroyed important fossils).

• All of the above.

Multiple Choice

Subdivision of a period; shortest division of geologic time. 

• Eon 
• Era 
• Period 
• Epoch 

Multiple Choice

Subdivision of an eon (Paleozoic, Mesozoic, Cenozoic)

• Era 
• Period
• Epoch 
• Eon 

Multiple Choice

Very large division of geologic time; usually referred to as the longest division of time. 

• Era
• Epoch 
• Eon 
• Period

Multiple Choice

The system of time measurement involving the formation of and changes of the Earth. 

• Index Fossil 
• Geologic Time Scale 
• Law of Superposition 
• Preserved Fossil 

Multiple Choice

The age of the Earth is measured in _______ of years.

• millions

• billions

Multiple Choice

When an unstable element like uranium turns into a more stable element like thorium, it is called:

• plate drifting.

• transformation.

• a chemical reaction.

• radioactive decay.

Multiple Choice

The amount of time it takes for 50% of a sample of a radioactive element to decay is called its:

• decay rate.

• half-life.

• half-blood.

• lifespan.

Multiple Choice

The geological time scale is divided into units of time scale. Which is the correct order in descending duration?

• period, era, epoch, eon

• eon, era, period, epoch

• eon, epoch, era, period

• epoch, period, era, eon

First life on Earth

Stromatolites

layered rocks, lithified remnants of microbial communities with or without active microbes

Multiple Choice

What type of fossil is this?

• Mold

• Cast

• Trace

• Preserved

Multiple Choice

What type of fossil is this?

• Mold

• Cast

• Trace

• Preserved

Multiple Choice

Where would paleontologists more likely to find fossils?

• Igneous rocks

• Sedimentary rocks

• Metamorphic rocks

Used along with

• radioisotope dating

• stratigraphy

How do we learn about ancient life?

• Paleontologist look for clues to understand what happened in the past.

• A paleontologist is a scientist who studies the fossilized remains of all kinds of organisms.

• Fossils of single-celled organisms date as far back as 3.8 billion years.

• A fossil is a trace or imprint of a living thing that is preserved by geological processes.

• When an organism is trapped in mud or sediment, the resulting fossil becomes part of that sedimentary layer of rock.

What can we learn from fossils?

• How life forms have changed over time

• when extinction occurred

Fossil Record

• All the fossils that have been discovered worldwide make up the fossil record. The fossil record gives evidence of many of the different organisms that have lived during Earth's long history.

• Each fossil gives information about a single organism.

• But overall, it helps us to understand larger patterns of change.

Ways to describe the age of fossils

• Relative dating - determines whether a fossil was formed before or after another fossil

• Absolute dating - estimate the age of a fossil in years

How Life Forms Have Changed Over Time

• Over many generations, populations change.

• Fossils show the gradual change in limb structure.

• Other species have survived for a long time without much change.

When Extinction Occurs

• An extinction happens when every individual of a species dies.

• A mass extinction happens when a large number of species go extinct during a relatively short amount of time.

• Gradual environmental changes and catastrophic events can cause mass extinctions.

What is the geologic time scale?

• To keep track of Earth's long history, scientists have developed the geologic time scale.

• The geologic time scale is the standard method used to divide Earth's long 4.6-billion-year natural history into manageable parts.

• A tool to Earth's history.

A tool to Organize Earth's History

• Time intervals correspond to significant changes in Earth's history.

• Some are defined by mass extinctions or significant changes in the number of species

• Others are defined by major changes in the Earth's surface or climate.

• The largest divisions of the geologic time scale are eons.

Geologic Time

What can we learn from the past?

Multiple Choice

The Geologic Time Scale is a record of what?

• Old Geologists

• The known history of rocks and fossils.

• Sweet geology music

• A list of every living thing ever

Multiple Choice

What are fossils?

• Is the change over time in populations of related organisms.

• Are the remains or evidence of once living organisms.

• A chart that divides Earth history into different time units.

• Occurs when the last individual organism of a species dies.

Multiple Choice

What is a fossil record?

• The change over time in populations of related organisms.

• Occurs when the last individuals species dies.

• Is made up of all the fossils ever discovered on Earth.

• Remains or evidence of a once living organism.

Multiple Choice

Look at the picture... What is circled?

• A Mold

• A Cast

Multiple Choice

What is a MOLD?

• The IMPRESSION of an organism

• A fossil COPY of an organism in a rock.

• The preserved evidence of the ACTIVITY of an organism.

Multiple Choice

What is a TRACE?

• The IMPRESSION of an organism

• A fossil COPY of an organism in a rock.

• The preserved evidence of the ACTIVITY of an organism.

Multiple Choice

A bug stuck in amber is an example of what type of fossil?

• Cast

• Trace

• Mold

• Preserved Remains

Multiple Choice

Scientists study the width of tree rings to learn about past climate conditions.

• True

• False

Poll

Trace fossils give information about animal activity and movement.

• True

• False

Multiple Choice

Sedimentary rocks provide information about Earth geologic history.

• True

• False

​As ancient  plants and animals evolved over millions of years, they adapted to Earth’s changing environment. When landmasses split or climate changed, animals evolved in response. The fossils tell the story of this evolution. Because of this cause and effect, changes in the fossil record can tell us about changes in Earth’s environment.

​Fossils help scientists to discover previously unknown chapters in Earth’s history. For example, when scientists find tropical plant fossils in today’s Arctic, it means these regions were once much warmer. Clues such as this help scientists to understand the positions of ancient continents and how Earth’s climate has changed in the past. Fossils also provide evidence of how sea levels have changed or how the composition of the atmosphere has changed.

​Scientists can reconstruct ancient ecosystems and habitats using fossil records. By studying fossils in a particular rock layer, a scientist can describe what the animal and plant communities in that area were. They can compare these fossil communities with communities found today. This helps them build a picture of the environment the fossils came from and how it changed over time. From fossil information, they can even determine the ecological relationships between now-extinct organisms. If they found evidence of mass extinction, it would be possible to pinpoint a significant moment in Earth’s environmental history.

Multiple Select

Scientists learn about Earth’s environmental history by comparing the rock layers and fossils of different sites around the world. The diagram to the left shows the rock layers of two sites with slightly different histories. Examine them carefully. Which statements could best explain the difference between these two sites? Select all that apply.

•  Site 1 and Site 2 experienced rising sea levels.

• Site 1 experienced an environmental change that Site 2 did not.

• Site 1 and Site 2 experienced continental drift.

• Site 2 experienced an environmental change that Site 1 did not.

• Site 2 experienced an extinction event.

Fossil Review​

Multiple Choice

What are "trace fossils"?

• fossilized footprints or root tracks

• the preserved remains of dead plants and animals

• man-made fossil replicas

Multiple Choice

Fossilized bone is heavier than regular bone

• true

• false

Open Ended

How Can We Tell How Old a Fossil Is?

​Dating Fossils

​An important aspect to studying fossils is determining how old they are. Scientists can determine the age of a fossil in various ways. Some methods provide “absolute” ages. This means that we can say approximately how old the fossil is in years. Other methods provide “relative” ages. This is simply whether the fossil is older or younger than other fossils or rocks. Absolute dates are considered more precise than relative dates. However, with either type, the older the fossil is, the more difficult it is to date with precision.

​Radiometric Dating

​A common method for finding the absolute age of a fossil is radiometric dating. Radiocarbon dating is an example of this type of dating. Carbon is in the air we breathe, and all living things contain much of this chemical element. However, carbon occurs in two forms, C-13 and C-14. Plants and animals take up C-14 from the air while they are alive. After a plant or animal dies the C-14 in its body begins to break down into C-13, which is the more stable form of carbon. This process happens at a known rate. Therefore, by measuring how much C-14 is left in a fossil, scientists can determine how old the fossil is.

Multiple Choice

Scientists use radiometric dating to determine the relative age of fossils.

• true

• false

Multiple Choice

Scientists use radiometric dating to determine the absolute age of fossils.

• true

• false

​Radiometric Dating-Continued

​This technique is often used for dating human remains and artifacts from archaeological sites. If an object is older than 60,000 years or so, all of the C-14 will be gone and this dating method will not work. Most fossils are older than 60,000 years, so other types of radiometric dating are used instead, but the basic process is the same.

Fill in the Blanks

Radiometric dating is also know as

dating.