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6-8 > Earth Science
Grade level: 6-8 Subject: Earth Science Duration: Two class periods
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Students will understand the following:
1. Earth is believed to be approximately 4.6 billion years old.
2. The first life, in the form of bacteria, appeared on Earth approximately 3.6 billion years ago.
3. Primitive organisms inhabited Earth long before more advanced ones, such as fish, amphibians, reptiles, and mammals.
4. Human ancestors and modern-day humans are relatively recent arrivals on planet Earth.

For this lesson, you will need:
Research materials on the history of life on Earth
Computer with Internet access
A long, narrow sheet of paper to create a wall frieze going around all four walls of the room
5" x 7" index cards

1. Inform students that they are going to work as a class to create a time line of life on Earth.
2. Assign one of the following organisms to each student, or have students work with partners and assign one organism to each pair: bacteria, cynobacteria, plants, invertebrates, fish, amphibians, reptiles, birds, first mammals, Java man, Peking woman,Australopithecus boisei, Neanderthal man, Cro-Magnon man, modern-day humans.
3. Instruct students to use the research materials you have provided or the Internet to answer the question, “How many years ago did your organism first appear on Earth?” (Ohio Wesleyan University’sGeologic Time Web sitefor elementary school students will prove an excellent source).
4. Distribute index cards to students, and have them use markers to write on the index cards the names of their organisms and the approximate number of years ago they appeared on Earth (for example, “bacteria—3.6 billion years ago,” or “birds—200 million years ago”). Instruct students to include simple line drawings of their organisms on the cards. (They may draw microscopic organisms, such as bacteria, as if seen under the lens of a microscope.)
5. Use narrow paper to create a frieze going around all four walls of your room, explaining that students will use the frieze to create their time line. Elicit from students that the time line is so long because Earth is estimated to be 4.6 billion years old.
6. Here is one way to divide the time line: use one wall to represent 4.6 billion to 3.6 billion years ago; use the second wall to represent 3.6 billion to 2 billion years ago; use the third wall to represent 2 billion to 1 billion years ago; use the fourth wall to represent the most recent billion years. Divide the fourth wall into tenths, each tenth representing one hundred million years. Explain to the students that the scale is not exactly correct, but the numbers are so large that it will give them a good idea of relative time periods.
7. Have students tape their index cards to the appropriate part of the time line.
8. Ask the students what observations they can make about the history of life on Earth based on the time line. They should note that, during Earth’s first billion years, no life existed at all. They should also recognize that most of the cards have been placed at the very end of the time line. What does this show us about the history of human beings as residents of our planet? (Students should conclude that we are relative newcomers, the earliest humans having appeared on Earth a mere 2 million years ago.) Students may also be interested to note that dinosaurs, mammals, and birds appeared on Earth around the same time (dinosaurs 240 million years ago, first mammals 225 million years ago, and first birds 200 million years ago).
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Adaptations for Older Students:
Challenge students to establish their own scale for the time line.
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Discussion Questions

1. Piece by piece, geologists put together evidence to begin to tell a story of what happened and is happening to create our dynamic Earth. Discuss how a geologist is like a detective.
2. List several ways tectonic forces have changed the face of the Earth.
3. Absolute geologic dating and relative geologic dating are two methods by which scientists try to determine the age of geologic evidence.Carbon-14 datingis an example of absolute dating, and thelaw of superpositionis an example of relative dating. Discuss the differences between absolute and relative geologic dating methods and how they can be used together.
4. The Earth has endured a great deal of weathering and erosion. Coastlines are impacted greatly by erosion. Discuss the forces of nature that cause this erosion. Now describe the methods coastal cities have instituted to reduce the erosion of their beaches.
5. How could you prove to a friend who doesn’t have a scientific background that the continents are still in motion and that they were once all joined together as the super continent Pangaea?
6. What theory explains why catastrophes occur every 30 million years?
7. During the history of the Earth there have been five mass extinctions. One of those mass extinctions eliminated the dinosaurs. Discuss what catastrophic events occurred to cause such a mass extinction.
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You can evaluate your students on their findings using the following three-point rubric:
  • Three points:accurate dating of organism, careful drawing of organism, correct placement of index card on time line
  • Two points:accurate dating of organism, no drawing of organism, correct placement on time line
  • One point:accurate dating of organism, no drawing, incorrect placement on time line
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Earth History Trivia
Present this scenario to your students: You are the writer for the game showCatastrophic Events on Earth. Your job is to create activities that will teach and review the catastrophic events that have shaped Earth. You may want to include information about the mass extinctions, the ice ages, volcanic and tectonic activity, comets, meteorites, asteroids, and anything else you can think of that has affected today’s ecology and geology. Make game cards with a question on one side and the answer on the other. Play the trivia game in pairs, or divide the students into two groups.

Mountain Creation Debate
Most mountain ranges are reflections of tectonic plate movement, but there is no single widely accepted hypothesis on mountain building. Have your students research one of the following hypotheses: the contraction hypothesis, the expansion hypothesis, the convection hypothesis, and the drift hypothesis. Next have your students pick a hypothesis to support during a class debate.

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Suggested Readings

Life: A Natural History of the First Four Billion Years of Life on Earth
Richard Fortey. Alfred A. Knopf, 1998.
A compelling book by a senior paleontologist at London’s Natural History Museum,Lifetraces the origin and history of life on Earth with unique insights. The author draws upon his own experiences as a paleontologist and writes in a very readable style that holds the readers’ interest.

Fanfare for Earth: The Origin of Our Planet and Life
Harry Y. McSween, Jr. St. Martin’s Press, 1996.
The author traces the origin of the Earth from its birthplace in the nebulae to the development of evolutionary theory.

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Discovery Online: Great Balls of Fire
Provides information about meteorites, has great graphics, plus a quiz about when different meteorites hit Earth.

1st-Order Global Tectonic Elements
Provides maps for each period of the Earth’s changing tectonic plates.

Exploring the Ocean Planet
Great graphics of Earth’s features.

Hamelin Pool Marine Nature Reserve
Features a description of the natural area and the formation of stromatolites.

U.S. Geological Survey
Lots of information on geology including, maps and image access.

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Click on any of the vocabulary words below to hear them pronounced and used in a sentence.

speaker    asteroid
Definition:One of a group of planetlike bodies whose general orbit around the sun is between Mars and Jupiter.
Context:Asteroids are found between Mars and Jupiter; these celestial bodies probably originated from meteorites.

speaker    basalt
Definition:A dark gray to black, dense to fine-grained igneous rock that consists of basic plagioclase, augite, and usually magnetite.
Context:Basalt, an igneous rock found in remnants of lava flows has been used by geologists to determine the relationships of land masses and rock formations.

speaker    lithosphere
Definition:The crust and upper part of the mantle of Earth.
Context:Our lithosphere continues to change as new landforms are created due to the movement of crustal plates.

speaker    meteorite
Definition:Matter that has fallen on the Earth from outer space.
Context:Meteorites provided the rock material necessary for the Earth to grow.

speaker    stalactites
Definition:Deposits of calcium carbonate hanging from the roof of a cave.
Context:The scientists investigated the stalactites hanging from the roof of the cave because they felt it would give them the age of the cave.

speaker    stalagmites
Definition:Deposits of calcium carbonate standing as pillars on the floors of caves.
Context:The stalagmites in the cave formed as calcium carbonate dissolved in water, permeated through the Earth’s surface, and was gradually deposited on the cave’s floor.

speaker    stromatolites
Definition:Laminated sedimentary fossils formed from layers of blue-green algae.
Context:As geologists analyze core samples, they look for stromatolites to assist them in determining the ages of different rock layers.

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This lesson plan may be used to address the academic standards listed below. These standards are drawn from Content Knowledge: A Compendium of Standards and Benchmarks for K-12 Education: 2nd Edition and have been provided courtesy of theMid-continent Research for Education and Learningin Aurora, Colorado.
Grade level:6-8, 9-12
Subject area:Earth science
Understands basic Earth processes.
(6-8)Knows that the Earth’s crust is divided into plates that move at extremely slow rates in response to movements in the mantle.

(6-8)Knows how landforms are created through a combination of constructive and destructive forces (e.g., constructive forces such as crustal deformation, volcanic eruptions, and deposition of sediment; destructive forces such as weathering and erosion).

(6-8)Knows how successive layers of sedimentary rock and the fossils contained within them can be used to confirm the age, history, and changing life forms of the Earth, and how this evidence is affected by the folding, breaking, and uplifting of layers.

(6-8)Knows that fossils provide important evidence of how life and environmental conditions have changed on the Earth over time (e.g., changes in atmospheric composition, movement of lithospheric plates, impact of an asteroid or comet).

(9-12)Knows effects of the movement of crustal plates (e.g., earthquakes occur along boundaries between colliding plates; sea floor spreading occurs where plates are moving apart; mountain building occurs where plates are moving together; volcanic eruptions release pressure created by molten rock beneath the Earth’s surface).

(9-12)Knows methods used to estimate geologic time (e.g., observing rock sequences and using fossils to correlate the sequences at various locations; using the known decay rates of radioactive isotopes present in rock to measure the time since the rock was formed).

Grade level:6-8
Subject area:science
Understands the nature of scientific inquiry.
Understands the nature of scientific explanations (e.g., emphasis on evidence; use of logically consistent arguments; use of scientific principles, models, and theories; acceptance or displacement based on new scientific evidence).

Grade level:6-8
Subject area:geography
Knows the physical processes that shape patterns on Earth’s surface.
Knows the major processes that shape patterns in the physical environment (e.g., the erosional agents such as water and ice, earthquake zones and volcanic activity, the ocean circulation system).

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Bryan Goehring, an earth science teacher at Blair Middle School in Silver Spring, Maryland.
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