EARTH
CLASSIFIED INFORMATION
The third planet from the Sun is our Earth. It is a member of the terrestial planets. Earth is the only planet in our solar system capable of supporting life. It is the only planet that we can survive on with ease. It contains the elements and components that are neccessary for our survival. Earth is perfect for us. It should be, for we came from it.
Earth is a unique planet in our solar system for one reason: it can support life. Earth can support life because of its compostition. It is at a perfect distance from the Sun; not too hot, not too cold. A temperate climate. Earth is 94 million miles (150 million km) from the Sun. Earth's size allows it to have the perfect condition for life. It has normal gravity which makes moving about easy without the difficulty of heavy gravity and low gravity. Earth's diameter is 7,926 miles (12,756 km). Earth is a small world compared to the large gas giants but it size is just right. In all, there would be great difficulty finding another planet like Earth.
Earth orbits the Sun in 365.25 days. This explains why every four years we have 366 days, or a leap year. Earth orbits the Sun at a speed of 18 miles a second (30 km a second). Earth orbits the Sun on an axis of 23 degrees . That angle is why the northern hemisphere experiences summer while the southern hemisphere experiences winter and vice versa. When it is summer in the northern hemisphere, more direct rays from the Sun are hitting because it is closer than the southern hemisphere, where less direct rays are hitting. Earth rotates on its axis every 23 hours 56 minites.
The Earth was formed 4,600 million years ago. At this point the lighter materials of its composition moved outward as the heavier materials sank inward to its core. As you go deeper into the Earth, both temperature and density increase. The innermost layer of Earth is the core. The core is composed of solid iron with a outer core of liquid iron and nickel and sulfur surrounding it. At the core, the temperature is 5,400 degrees F (3,000 degrees C). This heat is caused by the radioactivity of some of the rocks. Surrounding the core is a mantle of fluid that is composed of rocks that are plastic and can be five times as dense as water. Above this mantle is the rocky crust. This is the surface of Earth. It is a few miles deep but is thinner under the oceans.
The magnetic poles are caused by the rotation of iron and nickel inside the core. These materials act like an enormous magnet with its poles near the geographic poles. A compass needle does not point North to the north geographic pole but North to the north magnetic pole. But because they are so close to each other there is not much difference.
The Earth is constantly in motion. The crust is made up of plates of all differnt sizes and shapes. These plates are constantly moving and interacting with each other. The interaction of plates is what creates mountain ranges, ocean trenches, and other landforms. The plates move so much that at one time there was only one continent, a supercontinent called Pangaea. Pangaea began to split apart to form the present day continents about the time of the dinosaurs.
Earth is capable of supporting life because it contains water. In fact, Earth is the only planet that contains water in all three forms; liquid, solid, and gas. The surface of Earth is covered in water. Oceans cover two-thirds of the planet.
The atmosphere of Earth is composed mainly of carbon dioxide, oxygen and nitrogen. The lower atmosphere has mainly oxyegen and nitrogen. This is the air we breath. There are small amounts of helium, carbon dioxide, argon and water vapor. The region in the atmosphere called the troposphere is where all weather takes place. In the troposhere, the temperature decreases with height. The troposphere is about 7 miles (12 km) high. Above the troposphere is a layer very vital to our survival, the stratosphere. Here, there is a thin layer of ozone 21 miles (35 km) above the surface, that shields the surface from harmfull ultraviolet radiation from the Sun. Ultraviolet sunlight that breaks oxygen atoms that collide forms the ozone which absorbs all the harmful radiation before it reaches the troposphere.
Earth's atmosphere extends 300 miles (500 km) above the surface of Earth. There are a few atmosphereic particles found even higher. The magnetosphere, or Earth's magnetic field, extends 60,000 miles (100,000 km) on the day side of the planet and farther on the night side. This field protects us from the solar wind from the Sun.
The formation of an atmosphere fit for us was caused by the algae, or microscopic plants, in the oceans thousands of millions of years ago. The algae breathed the carbon dioxide, and exhaled oxygen. Over time this allowed organisms to begin to habitat the land and eventually create the planet full of life that we know today.
Earth
is the innermost planet to have a moon. Once active, the moon is now dull
and barren. Covered with craters, the moon is lifeless. There is recent evidence
that there is water on the moon which gives us reason to visit it again and
maybe begin its colonization. The moon is of average size and is large enough
to be sphereical. The moon orbits the Earth about every 29 days, or every
month. Its orbit creates the rise and fall of the tides. From Earth, only
one face of the moon is seen. The other face was not seen untill our voyages
there began.
Diameter . . . . . . . . . . . . . . . .7,926 miles (12,756 km)
Atmosphere. . . . . . . . . . . . . . 78% nitrogen, 21% oxygen
Mass . . . . . . . . . . . . . . . . . . 5,975,000,000,000,000,000,000,000 tons
Temperature (average) . . . . . . .72 degrees F (22 degrees C)
Distance from the Sun . . . . . . .94 million miles (150 million km)
Degree of Axis . . . . . . . . . . . .23.44š
Length of Day . . . . . . . . . . . . 23 hours 56 minutes
Length of Year . . . . . . . . . . . .365.25 days
Credits: Photographs; "Courtesy Jet Propulsion Laboratory. Copyright (c) California Institute of Technology, Pasadena, CA. All rights reserved. Based on government-sponsored research under contract NAS7-1260."
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