By : Barbara and Sarah

How were the Continents Formed?

• Tectonic plates carried a number of land masses together to form a single continent, called Pangaea, which was surrounded by an ocean called Panthalassa. Then, beginning about 200 million years ago, Pangaea broke apart into the northern continent of Laurasia and the southern continent of Gondwanaland. The modern basins of the Pacific, Atlantic, and Indian oceans began to take shape about 120 million years ago, when Laurasia broke apart into Eurasia and North America, while Gondwanaland split into Africa, Antarctica, Australia, India, and South America.

The Earth’s crust

• Just under the earth’s crust are thick layers of hot rock, this hot rock surrounds a ball of mostly hard metal at the center of the earth. Earth has three layers of hot rock and metal. All dry land and ocean floors are a part of the earths crust too. Earth’s crust is like a hot rocky shell. The crust is about 25 miles and 40 kilometers thick.

The Troposphere and the Stratosphere

Troposphere• The troposphere helps

maintain the temperatures on the earth’s surface it allows sunlight to pass through the other layers. This layer of the atmosphere moves.

Stratosphere• The stratosphere begins

six miles above the earth’s surface. The stratosphere is nearly cloudless and really dry except there are ice clouds during the winter. This layer of the atmosphere is still.

The Mesosphere and the Thermosphere

Mesosphere• The lowest temperatures

occur in earth’s atmosphere is the mesosphere. The mesosphere gets the coldest in the summer because winds and storms cause waves of air to form in the troposphere.

Thermosphere The air is extremely thin in

the thermosphere; the thermosphere contains mostly hydrogen and helium. Daily and seasonal changes in the solar activity causes the temperatures in the thermosphere to vary.

The Exosphere• The exosphere is 341 to 434 miles above the

earth. The exosphere is made up of mostly hydrogen. Artificial satellites generally orbit in this region.

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CreditsDutch, Steven I. "Earth." World Book Student. World Book, 2012. Web. 26 Oct. 2012.

Moran, Joseph M. "Troposphere." World Book Student. World Book, 2012. Web. 26 Oct. 2012.

Ramanathan, Veerabhadran. "Stratosphere." World Book Student. World Book, 2012. Web. 26 Oct. 2012.

Hitchman, Matthew H. "Mesosphere." World Book Student. World Book, 2012. Web. 26 Oct. 2012.

Moran, Joseph M. "Thermosphere." World Book Student. World Book, 2012. Web. 26 Oct. 2012.

Crust." World Book Kids World Book, 2012. Web. 26 Oct. 2012.

http://www.reference.com/browse/Exosphere