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.
Grade Span: K2
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
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 everybodys 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:
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 hasnt always stayed the same.
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