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Lesson Plans: Exploring Geologic Time and The Burgess Shale Fossils


Students gain an understanding of Geologic Time in this hands-on activity, by building a physical model of the Geologic Time Scale. Some important developments in the evolution of life on Earth are illustrated and highlighted on the timeline, including the famous Burgess Shale fossil site, an UNESCO World Heritage Site located in Yoho National Park . Some mathematical calculations are required.

Learning Expectations:

  • to make a correct scale model of the Geologic Time Scale, showing its basic divisions of time
  • to summarize, and place in order some of the major developments in the history of life on Earth
  • to appreciate the great age of the Burgess Shale fossils, and why they are designated a UNESCO World Heritage Site

Duration of the lesson:

Approximately one hour to actually build and label the timeline, assuming that all materials are previously collected. In and out of class research time (ranging from 1-3 hours), if desired.

Required Materials/Preparation:

  • 4 different colours of thick yarn (you will need about 4 metres of one colour, and small amounts of the other colours)
  • metric ruler or measuring tape
  • scissors
  • colour markers
  • masking tape or flagging tape, copies of Tables 1 & 2 (included here)
  • calculator
  • *computer, with Internet access (optional)
  • *construction paper and pictures corresponding to the major events, string (optional)

Teacher Background:

  • Students should know how to use a mathematical ratio to create a scale model, as well as be able to do basic metric conversions.
  • The Background Information section gives more details about each of the events listed in Table 2. Answers to the Discussion Questions are located within the text of the Background Information section.
  • Small groups may work together to build their own version of the timeline, then present theirs to the rest of the class. Illustrations representing each of the events (in random order) could be handed out to another group, and they could be asked to arrange the events on the timeline. The teacher can facilitate this exercise by encouraging participants to think about what had to happen first, in order for higher life forms to evolve (e.g. plants had to be present on land as a food source, before animals could move to land).
  • Answers to Tables 1 and 2, and to the Discussion Questions are included.


  • Refer to Table 1: Major Divisions of Geologic Time. Complete the table, using a calculator, to calculate the length of yarn that should be used to represent each major division of the geologic time scale (use the scale 1 cm = 10 million years).
  • Use a different colour of yarn to represent each of the 4 divisions of time, and cut the lengths of yarn according to your calculations in Table 1. (You may need to add an extra 10 cm or so to each piece, to allow you to tie the pieces of yarn together.) Now you will have a colourful representation of the geologic time scale! (Make sure that when your lengths of yarn are tied together, the time periods remain approximately the correct length according to your calculations.)
  • Place a large knot at the beginning of Precambrian time on your timeline to represent the Formation of the Earth, 4.5 billion years ago. This will be your datum or starting place from which to measure to the next event. Label this event using colourful tape (or a suitable picture glued onto construction paper and hung on a string).
  • Complete Table 2: Major Events in Earth’s History, using the scale 1 cm = 10 million years (or 1 m = 1 billion years).
  • Starting from the first knot, tie a 2 nd knot the correct distance away (to represent the appearance of Simple Cellular Life, 3.5 billion years ago, or 1 billion years after the Earth had formed). Label this important event with tape, or a picture.
  • Continue to tie knots along the string at the correct distances from the previous knot to represent each important event in Earth’s history listed in Table 2. Label what you think are the most important events. Your timeline is now finished and ready to present to the rest of the class!

Table 1: Major Divisions of Geologic Time (10 million years = 1 cm)

 Time range
(millions of years)
Length of period (millions of years)Length in cm (1 cm = 10 million years) *round to the nearest cm
Precambrian Eon 4,500 – 543 3,957 396
Palaeozoic Era
(“ancient life”)
543 - 248    
Mesozoic Era
(“middle life”)
248 - 65   18
Cenozoic Era
(“recent life”)
65 – 0 (present day) 65  


Table 2: Some major events in Earth’s history (10 million years = 1 cm)

KnotEvent Millions of years agoDistance from previous knot (cm)
1 Formation of the Earth (Datum) 4,500 0
2 Simple Cellular Life appears 3,500 100 cm
(4500-3500 =1 b.y. = 1m)
3 Cambrian Explosion (abundant fossils) 543 (3500-543) =2957 m.y. = ?cm
4 Burgess Shale fossils 505  
5 First Plants on Land (Cooksonia) 410  
6 Insects appear 320  
7 Age of the Dinosaurs 175  
8 Flowering plants appear 140  
9 Cretaceous Extinction 65  
10 Early humans appear 4  


Discussion Questions:

  • What can be observed about the history of life on Earth from the timeline?
  • About what percentage of Earth’s history is represented by Precambrian time?
  • What chemical process allowed for the build-up of oxygen in the Earth’s atmosphere over time? What life forms were responsible for this?
  • What important event marks the beginning of the Palaeozoic era? What is the significance of this event?
  • Where were the Burgess Shale fossils first discovered? When were they found? By whom? Why are they important enough to be designated an UNESCO World Heritage Site?
  • What other major geologic event (that has shaped our landscape in western Canada) occurred during the Age of the Dinosaurs?
  • What major event marks the close of the Mesozoic era?
  • How significant is the time in which humans have lived on Earth relative to the great age of the Earth?


The teacher could assess students using any or all of the following criteria:

  • Tables 1 and 2 correctly completed
  • timeline is correctly built to scale, major divisions of time are apparent with colour-scheme used
  • timeline is neat and is labelled correctly
  • appropriate illustrations are used to represent the major events, and are correctly positioned
  • Discussion Questions are answered correctly
  • student demonstrates understanding by an ability to tell others about the timeline

Extension of the lesson:

  • If time allows, students could find illustrations representing each of the major events, and label the timeline with these.
  • Rather than providing the students with the Background Information given here, the teacher may wish to have the students research themselves to find out more about the major events in the history of life on Earth listed in Table 2.
  • Only some of the major events in Earth’s history are listed in Table 2. The teacher could build on this activity by asking students to create their own version of Table 2.
  • Only the largest divisions of the Geologic Time Scale are given in Table 1. The teacher may ask students to show more divisions of the Geologic Time Scale on their timeline than are given in Table 1.

Suggested Related Resources :

These are only some of the additional resources you may wish to use in order to expand the scope/research for this lesson.


Main reference:

This web-lesson was created by teacher Lisa Holmstrom, 2005.

Background Information:

The first evidence for life on Earth comes from fossils of simple bacteria and cyanobacteria in rocks that are 3.5 billion years old. However, it wasn’t until the dawn of the Palaeozoic era (start of the Cambrian period) when life on Earth suddenly became abundant. Complex life has only existed on Earth for about the last 12% of Earth’s long history!

The main divisions of geologic time are defined by major events in the Earth’s history that are recorded in the fossil and/or rock record.

Some Significant Events in the History of the Earth:

Formation of the Earth

The estimated age of the Earth is 4.5 billion years old. At this time, Earth was a nasty place with a poisonous atmosphere and no signs of life anywhere. Gradually, an atmosphere of carbon dioxide, hydrogen, helium, nitrogen, methane and water vapour built up from volcanic eruptions and meteors crashing into Earth. From this primitive beginning, the first life developed, and the atmosphere gradually changed to contain more and more oxygen, capable of supporting higher life forms.

Simple Cellular Life

A billion years after the planet formed, the first lifeforms, bacteria and cyanobacteria, were present. They formed mats in shallow tidal environments, and these mats trapped small particles of sand and other sediment to build structures called stromatolites. They had the ability to photosynthesise, i.e. use sunlight and CO 2 to make food, and in the process they gave off oxygen. As a result of their life processes, oxygen gradually built up in the Earth’s atmosphere and in the oceans.

Cambrian Explosion

It was the Big Bang of evolution! In a very short time period, an abundance of fossils suddenly appeared in the fossil record showing that a large diversity of complex, multicellular animals were living in Earth’s oceans at this time. This important event marks the beginning of the Palaeozoic eon. For the first time, many different animals acquired the ability to produce hard shells for protection. Trilobites, ancient marine arthropods, were present in great numbers in the Cambrian oceans, and were the first animals to develop eyes and the ability to see.

Burgess Shale fossils

These world-famous fossils are found in Yoho National Park in British Columbia. They were first discovered by Charles Walcott in 1909. They represent a tremendous variety of plants and animals that lived in a warm, tropical, shallow sea. Some of these animals are ancient ancestors of animals alive today, but others are long extinct, and are nothing like creatures alive today! They lived a short time after the Cambrian Explosion, and are important to science because they are so old and so well preserved (even the soft tissues and membranes of the animals are preserved 505 million years after they died)! Today, the fossils rest in what is known as Walcott’s quarry, high up on a mountain ridge near the village of Field.

First Land Plants

The earliest known fossil land plants are from the Devonian period, and have been found mainly in Australia. These plants were quite small, and are called Cooksonia. Their stems were usually only a few centimetres high, and they lacked leaves and true roots. They were the first lifeforms to colonise the land!


Hundreds of fossil insect species date back to the Pennsylvanian Period, 320 million years ago. Early insects were wingless, and related to living silverfish. When wings finally evolved, they initially projected out to both sides, but later, could be folded back along the body. Certain advanced groups such as those that interact with flowering plants (like bees, wasps, flies, and ants) do not appear in the fossil record until flowering plants evolved.

Age of the Dinosaurs

The Jurassic period (208 – 146 million years ago) was the age of the dinosaurs! The two main groups of dinosaurs were the Saurishians and the Ornithischians. The first group evolved from early reptiles, and had a pelvis like that of many other reptiles. The second group evolved from the Saurishians. This group had a birdlike pelvis. Dinosaurs would rule the land for over one hundred million years! At the time that dinosaurs were roaming the coastal plains of Alberta, the Rocky Mountains began to rise to the west.

Flowering Plants

Flowering plants appeared on land during the Mesozoic, about 40 million years ago. Much of their evolution was based on the symbiotic relationship that developed between insects and plants.

Cretaceous Extinction

A major environmental crisis occurred within a short period of time, at the close of the Cretaceous period at the end of the Mesozoic era. Dinosaurs, large clams, ammonites, and other animal groups vanished in less than a million years. A large asteroid struck the Earth just offshore of the Yucatan peninsula in Mexico at this time, creating a tremendous explosion and firestorms that sent huge amounts of dust and debris up into the Earth’s atmosphere that blocked out the sun. Evidence for such an impact is found in unusually high concentrations of the rare element iridium, found in clay layers in many places around the world dating from this time period. The iridium is believed to come from the asteroid. Convincing evidence of this theory was provided when an oil company discovered the asteroid’s crater beneath the bottom of the sea. However, there is evidence that an environmental crisis was already in progress and was causing extinctions before the asteroid impact, but the asteroid was the final blow to the dinosaurs. There were at least 4 other periods of mass extinctions on Earth prior to this one.

Early Humans

The first early humans (hominids), from the family Hominidae, appeared on Earth about 4 million years ago. The hominids were characterised by upright posture, and their forelimbs were not used for locomotion and so were usually shorter and not as strong as the hind limbs. In addition, the teeth were small and were about the same size, in contrast to the larger teeth of apes and monkeys.

Answers :

Table 1: Major Divisions of Geologic Time
 Time range
(millions of years)
Length of period (millions of years)Length in cm (1 cm = 10 million years) *round to the nearest cm
Precambrian Eon 4,500 – 543 3,957 396
Palaeozoic Era
(“ancient life”)
543 - 248 295 30
Mesozoic Era
(“middle life”)
248 - 65 183 18
Cenozoic Era
(“recent life”)
65 – 0 (present day) 65 7

Table 2: Some major events in Earth’s history
KnotEvent Millions of years agoDistance from previous knot (cm)
1 Formation of the Earth (Datum) 4,500 0
2 Simple Cellular Life appears 3,500 100
3 Cambrian Explosion (abundant fossils) 543 296
4 Burgess Shale fossils 505 4
5 First Plants on Land (Cooksonia) 410 9.5
6 Insects appear 320 9
7 Age of the Dinosaurs 175 14.5
8 Flowering plants appear 140 3.5
9 Cretaceous Extinction 65 7.5
10 Early humans appear 4 6

Answers to Discussion Questions:

  1. For most of Earth’s history (the Precambrian), only the simplest lifeforms existed. Life became complex and much more diverse after the Cambrian Explosion.
  2. About 88% of Earth’s history is represented by Precambrian time ((4500-543)/4500 x 100%). Complex life has existed on Earth for only about 12% of the total time.
  3. Oxygen gradually built-up from the process of photosynthesis by cyanobacteria.
  4. The Cambrian Explosion. The Cambrian Explosion represents the sudden appearance of a great diversity of complex life in the fossil record.
  5. American Charles Walcott first discovered the Burgess Shale fossils in Yoho National Park in 1909. This site, known today as Walcott’s Quarry, remains the richest site, although there are other Burgess Shale sites found elsewhere in the world. The Burgess Shale animals lived shortly after the Cambrian Explosion, so are some of the oldest ancestors of modern animals. They are extremely well preserved, with even soft tissues and internal organs visible.
  6. The Rocky Mountains began to form, about 175 million years ago.
  7. Cretaceous mass extinction, when the last of the dinosaurs perished.
  8. Not very significant at all, less than 0.1% in terms of geologic time!

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