Last updated: August 16, 2022
Lesson Plan
Geologic Timeline
- Grade Level:
- Upper Elementary: Third Grade through Fifth Grade
- Subject:
- Science
- Lesson Duration:
- 60 Minutes
- State Standards:
- Colorado Academic Standards for Science: 4th grade: 2.2.a – Explain what fossils say, the similarities between fossil and living organisms. 2.2.b – Interpret evidence for past environments.
- Thinking Skills:
- Creating: Bring together parts (elements, compounds) of knowledge to form a whole and build relationships for NEW situations. Evaluating: Make informed judgements about the value of ideas or materials. Use standards and criteria to support opinions and views.
Essential Question
What can fossils tell us about the history of the Earth?
Objective
Students will learn the extent of Earth’s history and how life has evolved throughout the geologic timeline.
Background
Scientists have estimated that the Earth is 4.6 billion years old. During the first billion years of Earth’s history, life was completely absent. It was not until about 3.6 billion years ago that the first life form appeared on Earth. Colonies of single cell cyanobacteria are the first life forms that appeared on Earth. They formed algal mats and nodules called stromatolites. Stromatolites are therefore the first life form that appeared on Earth during the Precambrian Era.
At the beginning of the Paleozoic Era, the Cambrian Period, there was an explosion of life where many sea creatures like corals, fish and trilobites flourished. At this point in Earth’s history, life was still restricted to the oceans. Throughout the Paleozoic, life evolved immensely and the first amphibians, land plants (e.g., conifers) and reptiles began to exist.
About 250 million years ago, there was the largest extinction event the Earth has ever known, which marked the end of the Paleozoic and the beginning of the Mesozoic era. As a result of this extinction event, nearly all sea creatures went extinct and many changes took place on land. Dinosaurs took over and ruled throughout the entire Mesozoic era. During the Mesozoic, the Earth also saw the earliest mammals and birds evolve. Most of modern plant life (angiosperms –flowering plants) also originated during the Mesozoic.
Then, 65 million years ago, another massive extinction event occurred which marked the end of the Mesozoic era and the beginning of the Cenozoic era. Dinosaurs went extinct as a result of the event and mammals came to dominate the land. The Cenozoic era extends into present day. Human-like creatures have only been around on Earth the past 2 million years. However, humans have had a greater impact in Earth’s history than any other creature. Will our success lead us to our own downfall?
Preparation
You will need:
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Picture of the geologic timeline
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Pictures of prehistoric species
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Prehistoric Species Index
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String
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Paperclips or clothespins
Materials
An index of various prehistoric animals that you will use to create your geologic timeline. Follow the directions to mark interesting facts about the different organisms and what Era or Period they will represent on your timeline.
Download Prehistoric Species Index
Lesson Hook/Preview
Scientists have estimated that the Earth is about 4.6 billion (4,600,000,000) years old! Geologists and paleontologists have made a timeline of the Earth's history called the geologic timeline. This timeline is divided into chunks of time based on fossils we find from each one. These large chunks of time are called eras. Sometimes eras are further divided into periods. The Mesozoic era, when dinosaurs ruled, is divided into the Triassic, Jurassic, and Cretaceous periods. You can look at how the different eras are divided in the geologic timeline shown.
Each era is represented by a unique group of organisms that lived together during that time. Each era and period has been given a designated range of years. For example, the Triassic period lasted from 252 million years ago to 200 million years ago. Sometimes an organism only lived for part of an era or period. If a species only lived from 215 million to 200 million years ago, we would say that it lived in the Early Triassic.
Now you get to make your own geologic timeline!
Procedure
#1: Find a place to stretch out your string so it is off the floor and straight across. A good option is to tie it between two chairs and move the chairs apart from each other so the string is taut.
Your string now represents the entire length of life's history on Earth. You will be arranging the pictures of prehistoric organisms according to when they appear in geologic time. The oldest will be at the left end of the line and the youngest will be on the right.
For the first billion years of the planet's history, life wasn't yet present on Earth. It was only around 3.6 billion (3,600,000,000) years ago that the first forms of life finally appeared! Colonies of single celled cyanobacteria in the oceans were the first life forms to appear on Earth. They formed algal mats and nodules called stromatolites.
#2: Clip the picture of the stromatolites to the left end of the string with a paperclip or clothespin. This is when life first appears on your timeline.
During the Cambrian Period, at the beginning of the Paleozoic Era, there was a sudden explosion of life as new species started appearing rapidly. At this time, life was still restricted to the oceans. But sea creatures like corals, fish, and trilobites flourished. As the Paleozoic Era went on life continued to evolve and the first amphibians, land plants, and reptiles emerged.
#3: Look at the Prehistoric Species Index. Follow the instructions to mark the important information about each animal. Each species is labeled with the geologic period they lived in. Use this to put them in order of appearance on your geologic timeline.
Around 250 million years ago the largest mass extinction the Earth has ever seen wiped out most of life on the planet. Almost all of the sea creatures were killed off and things on land changed drastically. This extinction event marked the end of the Paleozoic Era and the beginning of the Mesozoic Era. The Mesozoic was marked by the long rule of the dinosaurs starting with their emergence in the Triassic Period. They then thrived until the end of the Cretaceous Period. During the Mesozoic Era, the earliest birds and mammals also evolved in the shadow of the titanic and bizarre reptiles that ruled. Most of today's modern plant life (flowering plants known as angiosperms) also appeared.
Then 65 million years ago another mass extinction wiped out the dinosaurs marking the end of the Mesozoic Era. Mammals took their new place as the dominant group on land. This marks the start of the Cenozoic Era which continues today. Human-like mammals have only been around for the past 2 million years. However, it has been known that humans have had a greater impact on Earth's history than any other species.
#4: A key for your geologic timeline is provided below. When you finish clipping all of your pictures to your string, look at the key to check where each species goes.
Vocabulary
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Geologic Timeline: noun; the billions of years since the planet Earth began developing
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Era: noun; one of the five major divisions of geologic time
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Period: noun; a division of geologic time longer than an epoch and included in an era
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Epoch: noun; a division of geologic time less than a period and greater than an age
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Precambrian: noun; the earliest era of geological history extending to the beginning of the Phanerozoic eon about 544 million years ago or the corresponding rocks
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Paleozoic: noun; an era in geological history ending about 248 million years ago in which vertebrates and land plants first appeared or the corresponding rocks
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Mesozoic: noun; the era of geological history between the Paleozoic and Cenozoic eras or the corresponding system of rocks
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Cenozoic: noun; an era of geological history that extends from the beginning of the Tertiary period to the present time and is marked by a rapid evolution of mammals and birds and of flowering plants and especially grasses; relating to the corresponding system of rocks
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Extinct: adjective; no longer existing
Assessment Materials
ReflectionWhat are some changes or patterns you notice looking at the organisms on your timeline?
Do you find it useful to see a reconstructed image of the species along with its fossil?
How do you think scientists are able to make reconstructions of extinct species?
Among the extinct species, are there any modern living organisms that look familiar?
Can you make any guesses as to what type of environment(s) some of the species lived in?
If you could go back in time to see one of the species along this trail, which would you choose? Why?
Rubric/Answer Key
ReflectionThis key starts from the first appearance of stromatolites and moves forward through time to present day.
- Stromatolites [Precambrian-Quaternary]
- Paradoxides [Cambrian]
- Orthoceras [Ordovician-Triassic]
- Cooksina [Silurian-Devonian]
- Temnospondyl [Mississippian-Pennsylvanian]
- Dimetrodon [Permian]
- Ginko [Permian-Quaternary]
- Neusticosaurus [Middle Triassic]
- Morganucodon [Late Triassic-Middle Jurassic]
- Pterodactylus [Late Jurassic-Late Cretaceous]
- Archaeopteryx [Late Jurassic]
- Triceratops [Cretaceous]
- Palaeochiropteryx [Eocene]
- Arsinoitherium [Oligocene]
- Mammuthus [Quaternary (Pliestocene-Holocene)]
- Homo sapiens [100,000 years-present]
Scientists can reconstruct what these organisms might have looked like by studying their fossils and comparing them to other living things that are similar to them.
A few of the organisms on your timeline are similar to living organisms such as the Ginko tree and modern Homo sapiens (like you).
Additional Resources
Check out our Geologic Timeline activity webpage for step by step instructions with pictures!