Fossils Provide Evidence of Environmental Changes

Fossils Provide Evidence of Environmental Changes

by Michaela Leys

Open Ended

How Do Fossils Provide Evidence of Environmental Changes That Occurred in the Past? (make your best guess)

​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.

Multiple Choice

Plants and animals evolve in response to 

• tractors

• climate change and continents splitting 

• fossilization 

• marine life

​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.

Fill in the Blank

Fossils provide evidence of how sea levels have changed or how the composition of the  ________ 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 Blank

Radiometric dating is also know as ________ dating.