"I Was So Much Older Then . . . "


Objectives: After completing the lesson, students will be able to:


Key Question: "What is the history of Earth?"



There are two key aspects for this lesson. First, the lesson provides the teacher with an opportunity to examine the students' knowledge base of the history of our solar system, Earth, and life on Earth. The teacher can also explore their prior understanding of how the key geologic features of Earth developed over time.

The second part of the lesson is designed to give students a basic outline of the geologic time scale, and how the creation and evolution of Earth fits into this time scale. If desired, the teacher can introduce some of the mechanisms that led to the development of Earth's geologic features and life forms.

Caveat: The time scale outlined in this lesson has changed dramatically in the last decade, as scientists extend our knowledge of "what happened when." It is important, therefore, to make sure that students understand the speculative nature of the history that is presented to them, no matter how sound the evidence seems for that history. Additionally, can be a valuable teaching strategy to lead students in a discussion about what future explorations of our solar system might teach us (e.g., the exploration of Mars; the recent launching of a satellite designed to collect solar particles).


Time required: anywhere from 1 to 3 days. There is a great deal of flexibility with this lesson (much of the flexibility depends on the teacher's knowledge base on this topic). 2-3 days (at 45-50 minutes each) is a reasonable time frame for a fairly thorough presentation of the lesson.



for the Class

    2 rolls of butcher paper, each at least 6 meters in length.



for each group of 3-4 students:

      Post-it notes

      crayons, markers, or colored pencils

      meter sticks


            The night before: draw a line the length of each roll of butcher paper. Measure and mark each line at one-meter intervals. Tape one of the lines to a wall of the room visible by all students.

   Day One:

Explain to the students that the line on the paper represents a timeline of the history of our solar system. Their first task is to determine a scale for the line. Discussion should lead to agreement on a scale in which 1 meter represents 1 billion years (if necessary, let the students know our Sun formed about 6 billion years ago). Have each group examine the meter sticks at their tables. Demonstrate how the different scales of the metric system represent varying amounts of time: 1 mm = a million years; 1 cm = 10 million years; 1 dm = 100 years; and, 1 m = 1 billion years.

Have the resource monitors distribute post-it notes and colored pencils (crayons or markers will also work) to their groups. Through class discussion, develop a list of the key events that have taken place in our solar system. The teacher can add items as they see fit (see below for a list of events and when they occurred). Working in groups, the students come to consensus about the time frame in which each event occurred. Then, each group writes a symbol for an event on a post-it, and their group number, and places the post-it on the timeline, in the proper location. Demonstrate again how the meter sticks can be used to locate time points on the timeline. This process continues until all the events on the list are placed on the timeline. The following discussion should focus on observed patterns in the students' guesses, incongruities in the sequence of events, and rationales for why students made the guesses they did.  Through this discussion, the teacher is able to determine the prior understanding students have about geologic time and the evolution of Earth.


   Day Two:

            Place the second, blank, timeline under the first (or simply remove the post-its from the first). Provide each group with a set of events and the correct timeframe for each. Have them create a symbol for each event on post-its, and place their events at the correct time points on the line. A brief narrative by the teacher should focus on the concept of geologic time, the various categories of geologic time (see the attached chart), and the processes that formed the key geologic and meteorological features of Earth. This process can be accomplished in a single day (for a brief overview) or can last as long as a week (for a very thorough treatment).

            Two articles that follow below present similar treatments of this topic that would be appropriate for a follow-up to the activities of the first day. While each takes a slightly different approach, the general sense of development of Earth over a great time span is key. These two lessons have the advantage of being student-centered, and group oriented. They also produce a product and process that is directly assessable. The first uses the same timeline device, but over a much larger distance (the timeline produced was more than 80 meters in length). The second replaces the timeline with a calendar, in which each day equals 12.6 million years.



            Groups can be assessed on the various tasks they have been asked to perform. These would vary, according to which approach was chosen for the second half of the lesson. Groups could be given a set of questions based on the lesson and homework readings. Each group would then prepare a presentation that answers their question using the graphic prepared during the lesson as a visual aid.

            Students could be given a list of events, and a diagram of a clock face. Working individually or in groups, students would be required to place the events on the clock in the proper location.

            A standard test assessment on the lessons and homework can also be given.



Read: "An Outline of Earth History" (best done as an assignment after the first day and before the second). No information on permission to use available.

            Students could complete the " Geological Clock" activity as homework. This assignment could be worked into a Math lesson on measuring angles with a protractor. This would enable students to achieve a greater degree of accuracy in the location of key events in geologic time onto the clock.



OUSD Science Content Standards (State of California Science Content Standards):  An understanding of geologic time is necessary if students are to grasp the full meaning contained in OUSD Standards #2 (Astronomy) and #3 (Plate Tectonics and Earth's Structure). Without the large time scale, students will not be able to understand fully how geologic and stellar processes have unfolded. (This lesson also sets the stage for an understanding of State Standard #1: "Plate tectonics explains important features of the Earth's surface and major geologic events").



"Earth" in, The DK Science Encyclopedia. New York: DK Publishing, Inc., 1998, pp. 209-240.


Farndon, John. How the Earth Works: 100 ways parents and kids can share the secrets of the Earth. New York: Reader's Digest Association, Inc., 1996, p. 93.


Lindman, Arnold D., and Mark McCarthy. "The Dinosaurs Came in December: Putting Geologic Time Into Perspective" in, Earth at Hand: a collection of articles from NSTA's journals, collected by Sharon M. Stroud and Jeffrey C. Callister. Washington, D.C.: National Science Teachers' Association, 1993, pp. 4-5. (Permission is granted in advance for reproduction for classroom or workshop instruction.)


Palmer, Douglas. "Earth History: The Geological Timescale" in, Atlas of the Prehistoric World. New York: Marshall Editions, Ltd., 1999, pp. 162-169.


Villas, Janet. "Giant Geologic Timeline" in, Earth at Hand: a collection of articles from NSTA's journals, collected by Sharon M. Stroud and Jeffrey C. Callister. Washington, D.C.: National Science Teachers' Association, 1993, pp. 2-3. (Permission is granted in advance for reproduction for classroom or workshop instruction.)


Zihlman, Adrienne, et. al.  "An Outline of Earth History" in, The Human Evolution Coloring Book., 1982, pp. 2-12. A new edition of this book was published in February, 2001. It is not known if this article appears in the new edition.



The most important point for students to take from this lesson is the immense difference in scale between geologic and human time. The processes they study require vast expanses of time, a concept most students do not tend to appreciate.



Key Vocabulary:

            Geological time: comparative and absolute dating of pre-historic events have led to the development of a time scale stretching over 4.6 billion years, in which key periods of time-depending on the kinds of life that existed at given times- are grouped into eras.


Timeline of the History of Earth




(years ago)

Position on a Timeline

(1 meter = 1 billion years)

The Sun Forms

6 billion

6 meters

The Earth Forms

4.6 billion

4.6 m

The Moon Forms

4.5 billion

4.5 m

Age of Meteor Bombardment Begins

4.5 billion

4.5 m

Life Begins on Earth (bacteria)

3.5 billion

3.5 m

Age of Meteor Bombardment Ends

3 billion

3 m

Earth's Oceans Forms

3 billion

3 m

First Single Cell Organisms With a Nucleus Appear

2 billion

2 m

Oxygen Appears in Earth's Atmosphere

1 billion

1 meter

First Jellyfish Appear

600 million

60 cm

First Fish Appear

480 million

48 cm

First Trees

300 million

30 cm

First Dinosaurs Appear

300 million

30 cm

First Mammals Appear

200 million

20 cm

First Birds Appear

160 million

16 cm

First Flowers Appear

120 million

12 cm

Dinosaurs Become Extinct

65 million

6.5 cm

First Primates Appear

30 million

3 cm

First Humans Appear

1 million

1 mm





   A much more detailed "Timeline of the Earth" can be found in the book by L. Margulis and D. Sagan, titled What is Life.