Earth

Earth is the third planet from the Sun and the fifth largest:

    Orbit:         149,600,000 km (1.00 AU) from Sun
    Diameter: 12,756.3 km
    Mass:        5.9736e24 kg

     Earth is the only planet whose English name does not derive from Greek/Roman mythology. The name derives from Old English and Germanic. There are, of course, hundreds of other names for the planet in other languages.   In Roman Mythology, the goddess of the Earth was Tellus- the fertile soil (Greek: Gaia terra mater - Mother Earth).

    It was not until the time of  Copernicus (the sixteenth century) that it was understood that the Earth is just another planet.

    Earth, of course, can be studied without the aid of spacecraft. Nevertheless it was not until the twentieth century that we had maps of the entire planet. Pictures of the planet taken from space are of considerable importance; for example, they are an enormous help in weather prediction and especially in tracking and predicting hurricanes. And they are extraordinarily beautiful.

The Earth is divided into several layers which have distinct chemical and seismic properties (depths in km):        

0-40 Crust
40- 400  Upper mantle
400- 650  Transition region
650-2700   Lower mantle
2700-2890   D'' layer
2890-5150   Outer core
5150-6378   Inner core

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