Earth

The knowledge of Earth plays a crucial role in our lives. Earth is a minute dot in a vast universe of stars, galaxies, and empty space. Satellites can circle right round it in just a few hours. | | | | | | | | | | | | | | | | | | | | | | |
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Yet it is still large enough for our understanding of it to be barely elementary. But early in the 19th century, scientists discovered that the age of Earth was immense-now estimated at more than four and a half billion years-and that it has undergone immense changes during its history. | | | | | | | | | | | | |
Earth appears to be flat, but in reality it is almost spherical. It is a little flattened at the poles and bulges out a little at the equator. | | | | | | | | | | | | | | | | | | | | | | | | | | | |
  The Earth is divided into seven layers: the crust, upper mantle, transition region, lower mantle, D” layer, outer core, and inner core. “The crust varies considerably in thickness; it is thinner under the oceans, and thicker under the continents”. (Arnett1) The inner core and crust are solid, and the outer core and mantel layers are plastic or semi-fluid. Most of Earth’s mass is in its mantle and the rest is in its core. |
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The Earth is the third planet from the Sun and it is the only planet known to have life on it. The Earth formed around 4.5 billion years ago.[5] It is one of four rocky planets on the inside of the Solar System. The other three are Mercury, Venus, and Mars.
The large mass of the Sun makes the Earth move around it, just as the mass of the Earth makes the Moon move around it. The Earth also turns round in space, so different parts face the Sun at different times. The Earth goes around the Sun once...