Earth's Early Atmosphere

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					Name: ________________________________                                                 Class: ________

Teacher: ______________________________                                                 Date: ________

                                               HW #: ___
                                  Earth's Early Atmosphere
Directions: Read the following two paragraphs and answer the questions that follow in
   complete sentences!

         Earth's atmosphere is a mixture of gases, solids,
and liquids that surrounds the planet. It extends from
Earth's surface to outer space. The atmosphere is much
different today from what it was when Earth was young.
         Earth's early atmosphere, was produced by
erupting volcanoes, and contained nitrogen and carbon
dioxide, but little oxygen. Then, more than 2 billion years
ago, Earth's early organisms released oxygen into the
atmosphere as they made food with the aid of sunlight.
These early organisms, however, were limited to layers of
ocean water deep enough to be shielded from the Sun’s
harmful rays, yet close enough to the surface to receive
sunlight. Eventually, a layer rich in ozone (O 3) that
protects Earth from the Sun’s harmful rays formed in the
upper atmosphere. This protective layer eventually
allowed green plants to flourish all over Earth, releasing even more oxygen. Today, a variety of life forms,
including you, depends on a certain amount of oxygen in Earth’s atmosphere.

1. How many years ago did oxygen enter Earth’s atmosphere? ___________________

2. Why did early organisms have to live in certain layers of the ocean?

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3. What was Earth’s early atmosphere produced by? What gases did the atmosphere
   contain?

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4. What protects the Earth?

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5. Describe what you think the Earth looked like with the early Atmosphere.

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                            Class Work

Color the Earth and label each part of the Earth. Define each sphere.
        Lithosphere, Biosphere, Hydrosphere, & Atmosphere

				
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posted:9/25/2012
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