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Earth is the third planet from the Sun. It is the largest of the solar system's terrestrial planets, and the only planetary body that modern science confirms as harboring life. Scientific evidence indicates that the planet formed around 4.57 billion (4.57×109) years ago, and shortly thereafter (4.533 billion years ago) acquired its single natural satellite, the Moon.
Structure of the Earth
The Earth consists of several atmospheric, hydrologic, and mainly geologic layers. Its components are the crust, the mantle, and its core.
Earth's atmosphere
Earth's atmosphere is a layer of gases surrounding the planet Earth and retained by the Earth's gravity. It contains roughly 78% nitrogen and 21% oxygen, with trace amounts of other gases. This mixture of gases is commonly known as air. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation and reducing temperature extremes between day and night.
Tectonic Plates
Plate Tectonics, theory that the outer shell of the earth is made up of thin, rigid plates that move relative to each other. The theory of plate tectonics was formulated during the early 1960s, and it revolutionized the field of geology.
Rock Types
A knowledge of rock types is fundamental to many aspects of geography and especially physical geography. Both physical features and various human activities can be heavily influenced by the type of rock found in a particular area.
Definition: Weathering involves the breaking down of rocks due to their exposure to the earths atmosphere (i.e. to the weather).
Erosion operates closely with weathering.

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