The Earth

Did u know that our planet, Earth wasn't always thought of as a planet? Until the sixteenth century when Capernicus figured out that the Earth was another planet, which revolved around the sun, Greek astronomers thought the Earth was the center of the solar system. Also Earth is the only planet that its name didn't come from Greek/Roman mythology.

When earth was first discovered, astronomers were only able to study it with out spacecraft. It was not until the twentieth century that we had maps of the entire planet. Pictures taken of the planet are very important, not only because they aid in weather predictions, but they are also very beautiful.

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.

Most of the core is made of iron, but there may be lighter elements in it too. Temperatures at the center of the core can be as high as 7500K, which is hotter than the surface of the sun.

"Unlike the other rocky planets, Earth's crust is divided into several separate plates, which float around independently on top of the hot mantle below". (Arnett1) This is called the plate tectonics theory. This is created by two processes. The first is spreading which occurs when two plates move away form each other and magma gets in, creating a new crust. The second is subduction, which is the opposite. When this happens two plates collide and one ends up being destroyed in the mantle. There are eight major plates: The North American Plate, South American Plate, Antarctic Plate, Eurasian Plate, African Plate, Indian-Australian Plate, Nazca Plate, and Pacific Plate. Other than these plates are about twenty small plates.

The surface of the Earth is about 4.5 ~ 4.6 billion years old, although the oldest rocks are about 4 billion years old. This is said to be rare because they are older then 3 billion years old.

Water makes up 71 percent of the Earth's surface. Earth is also the only planet that can have water as a liquid on its surface. Water is very important on Earth because we need it to live, and without it we would be non-existent.

The Earth's atmosphere is made up mostly of