A Long Time Authors: Sharon Janulaw

Overview: In this lesson, the teacher puts up a time line that shows students age relative to geologic time.

Lesson Concepts:

• Life has been on Earth for a long time.

Grade Span: K–2

Materials:

• 37 meters of adding machine tape
• Adhesive tape
• Pictures of Cenozoic, Mesozoic, Paleozoic, and Precambrian living things. The urls below should help with this:
  — www.amnh.org/exhibitions/Fossil_Halls/Timelines/index.html/
  — www.rth.org/tarpits/
  — www.humboldt.edu/~natmus/Exhibits/Life_time/Mural.web/MurIndex.htm
  — www.carnegiemuseums.org/cmag/bk_issue/1999/marapr/feat2.htm
  — www.peabody.yale.edu/mural/

Advance Preparation:

— Put up the timeline with appropriate numbers using a scale of 10 meters equals a billion years (1 centimeter equals one million years) • Cenozoic: 0 to 65 cm, Mesozoic: 65 cm to 2.5 m, Paleozoic: 2.5 m to 5.5 m, Precambrian: 5.5 m to 37 m.
— Copy and cut out appropriate pictures for eras.
— Cut out a very small picture of a girl and a boy.

Time: 20 minutes

Grouping: Whole class

Teacher Background:

The earliest fossils date to about 3.7 billion years ago (bya). This is the beginning of the Precambrian Eon. Life for most of the Precambrian consisted of unicellular bacteria, but late Precambrian fossils include jellies and wormlike life. The Paleozoic Era began about 550 mya and was marked by the rise of arthropods (e.g., crustaceans and insects) as well as fish and amphibians. The Mesozoic Era (beginning at 250 mya) featured everybody’s favorite, dinosaurs, swimming reptiles, flying reptiles and early mammals. In the Cenozoic Era (from 65 mya to present), mammals rose to dominate the large fauna and birds colonized every continent.

It is important to note that all life today descended from Precambrian life and that there are many familiar examples of present-day life that are very similar to ancient forms. Examples include jellies, corals, sea stars, crawdads, sowbugs and dragonflies. Remarkably, opossums and shrews closely resemble mammals that shared the Earth with dinosaurs.

Teacher Resources: There are many high-interest books about prehistoric life in bookstores. Examples:
Maia: A Dinosaur Grows Up by John R. Horner tells an engaging tale.
Dinosaurs: The Biggest, Baddest, Strangest, Fastest by Zimmerman and Olshevsky is an excellent picture book with interesting text.

Explore these links for additional information on the topics covered in this lesson:

• Fossils
• Geologic Time
• History of Life

Teaching Tips:

The numbers on the timeline will be impressive but meaningless to children in this age group. The points to get across are that life has been on Earth for an extremely long time and it hasn’t always stayed the same.

Vocabulary: timeline

Procedure:

1. Ask students if they notice anything different on the classroom wall. What is on it? Tell them that this is called a timeline. A timeline is a way to show when things happened in the past.
2. Tell the students that you are going to use the timeline to take an imaginary trip back in time. “We’ll put pictures of things that lived a very long time ago on our timeline.”
3. Starting with the illustration of a girl and a boy on the very edge of the timeline, go backwards in time, placing appropriate illustrations on the timeline as you tell what lived in each era and mentioning how many years ago each lived.
4. Ask students what they think the timeline tells us. “What do we know from looking at the timeline?” Ask what they notice about the sorts of living things they see on the timeline. “How are they the same? How are they different?” Talk about how long the timeline is, that people are at the end of it and that life has been on Earth for a long time.