Time Line

One of the more difficult ideas for people of all ages to comprehend is the immensity of time over which the Earth has formed and evolved. While most people have some sense that Biology has an evolving history, the physical Earth has one too, and they are inextricably linked together. In this activity, the History of the Earth will be visualized, and significant events in the physical history and the history of life will be put in proper temporal relationship.

A. Teacher introduction

The Earth that we live on today is the result of many, many years of geological activities, some big and exciting, like earthquakes and volcanic eruptions, and some which, day to day, seem small and almost insignificant, like streams moving sand or animals being born or dying, or plates moving a few centimeters per year. Some of the significant events which have happened in Earth History include:

History of Life: (MY = million years before present)

  • First bacteria - 3500 MY
  • Abundant soft-bodied animals - 700 MY
  • abundant fossil invertebrates - 570 MY
  • First fish - 505 MY
  • Early land plants - 438 MY
  • First amphibians - 370 MY
  • First reptiles - 310 MY
  • Dinosaurs appear - 240 MY
  • First mammals - 225 MY
  • First birds - 200 MY
  • Flowering plants appear - 140 MY
  • Age of Mammals begins - 66 MY
  • Early horses and other familiar animals - 37 MY
  • Earliest humans - 2 MY
  • Modern Humans - 0 MY (now)

Physical Geology: (MY = million years before present)

  • Formation of Earth - 4600 MY
  • Oldest rocks yet discovered - 3950 MY
  • Significant oxygen in atmosphere - 1500 MY
  • Start of formation of Appalachian Mts. - 450 MY
  • Start of supercontinent Pangaea (all continents pushed together) - 360 MY
  • Abundant coal-forming swamps - 320 MY
  • Break-up of Pangaea begins - 225 MY
  • Massive volcanic activity marking opening of north Atlantic Ocean - 60 MY
  • Formation of Rocky Mts. - 60 MY
  • Major deformation of Alps and Himalayas - 50 MY
  • Ice Age which covered much of Ohio - 1.6 MY to 10,000 yrs
  • Hawaii (big island) eruptions start - 0.7 MY
  • Eruption of Mount St. Helens - 0 MY (May 1980)
  • Loma Prieta earthquake (“world series” quake) - 0 MY (1989)

Note to teacher: You can of course pick and choose and add events which fit in with what you have been doing in class. Ohio Geology, a publication of the Division of Geological Survey, for Fall 1996, presents a time-line for geological events for the part of the Earth’s surface now known as Ohio.

B. Student activity


  • Drawing paper - one sheet per student
  • Crayons, colored pencils, or markers
  • Measuring tape
  • Yarn or string
  • Masking tape


  1. Assign/choose one event per student. Each student draws a picture representing the event. (You may wish to have library books available which illustrate various fossil animals and plants, as well as mountains, volcanoes, and whatever you have chosen for representation on the time line.)
  2. Decide how long the full line will be, i.e. what distance will the age of Earth, 4.6 billion years, be represented by? Note: You will need a long space! This can be done down a long hallway or around the perimeter of the classroom.


    • 1" = 1 million years (383' = 4600 million years)
    • 0.5" = 1 million years (191.5' = 4600 million years)
    • 0.1" = 1 million years (38.3' = 4600 million years)
  3. Measure out the full distance of yarn/string, and tape to wall, at about average height of students, if possible.
  4. Depending on student ages/abilities, the next step can be a math exercise, or you can tell them the distance which corresponds to each event. For example, for scale 0.1" = 1 million years, the student who drew the abundant soft-bodied animals would calculate a distance of 0.1" x 700 MY = 70". Each student, after calculating or being given the distance, then measures that distance from the end (“now”) of the time line and marks it with a labeled masking tape tab, and tapes the drawing above or below the tab. When all events are placed, have students stand next to their events. Starting at the beginning of Earth, have students in turn call out their events, ending with some modern occurrence such as the eruption of Mount St. Helens, May, 1980, or a recent earthquake the students know about, e.g. the Loma Prieta (“world series”) Quake, October 17, 1989.
  5. Alternatively, as class, mark off every 100 million years on the yarn, using masking tape tabs, and have students place their pictures between the appropriate tabs. (For more recent events, you may wish to do an expanded time line, in order to fit in more events.)

The Record of Life on Earth: Fossils

This activity may be more appropriate than the Time Line to the abilities of younger children.

A. Teacher introduction

Start with a discussion of animals (and other life forms) to get the students thinking about what living organisms are and what they do. Ask what are the normal activities that animals engage in: eating, breathing, sleeping, etc. What activities are necessary to life? What body parts are necessary for each of these activities? What different methods can be used by animals to achieve these activities? What demands do these make on body part types? For example, compare animals which graze on grass to grazers of tree tops, to those which hunt meat; compare animals which breath air to fish getting oxygen from water through gills, etc.

Discuss what a fossil is - a record of past life. Have children imagine an animal and how that animal could be preserved as a fossil. Would hair or skin likely become a fossil? No - more likely to decay or be consumed by another organism. Would bones, teeth, shells be likely to become fossils? Yes, more likely because they are hard, and do not undergo as rapid decay, and are less appealing as food for other organisms.

B. Student activity


  • Variety of small fossils (they may be whole, or even better, a part or parts of organisms, or trace fossils such as foot prints or molds of other body parts)
  • Drawing paper
  • Crayons, colored pencils, or marker


  • Picture books on paleontology and on living animals
  • Display samples of fossiliferous limestone for students to see that fossils are preserved as parts of rocks


  1. Give each student a fossil, a piece of drawing paper, and access to crayons/markers.
  2. Assignment: Draw the fossil. Imagine what kind of creature this fossil was a part of - was this fossil the whole creature, or was it just a part of the life form. Draw the entire organism that you imagine from this fossil, showing the place of this fossil in the organism. If students need some prompting to get their creative ideas flowing, let them peruse picture books. Then draw the living environment you imagine for this organism. Did it live in the water or on land? If water, was it near a beach, or at the bottom of the ocean, or floating in the water? If land, was it forest, or Savannah, mountains, streams? When finished drawing the organism and its environment, suggest a living creature that might be a modern relative of the creature, possibly extinct, you just created. Students can then take turns telling the class about their imaginary creature and how they think it could have lived.
  3. Additional option: This activity could follow a field trip for students to collect their own fossils. Or, teacher could provide chunks of fossiliferous limestone for students to choose a fossil from.