Earth 

http://en.wikipedia.org/wiki/Earth

     The Earth is the most unique planet in the whole solar system. It is the only planet to have life on it so far. It is home to millions of species including us. The Earth was made 4.54 billion years ago. It is said that life appeared within a billion years after it was made. The Earth's magnetic field and ozone layer protect us from solar radiation which allows life to exist. The Earth is one AU away from the Sun. Sunlight takes about 8.3 minutes to reach the Earth. It is the largest and densest inner planet and the only planet known to have current geological activity. It is also the only planet with a liquid hydrosphere and plate tectonics. The moon is our only natural satellite that orbits us. The moon is what makes us have ocean tides. The Earth climate varies from hot, dry desserts to freezing cold ice caps.

Structure:

http://www.planetsalive.com/image/earxsec.jpg

     The Earth's core has two parts the outer core and the inner core. The inner core is solid iron and has a radius of 758 miles. The temperature here is thought to be close to the temperature on the surface of the sun. About 5500°C. The outer core is made of liquid iron and nickel. It has a radius of 5150 km. The outer core is thought to influence the Earth's magnetic field. The temperature of the outer core is around 4400°C.

      The Earth's mantle is relatively solid. It's is 1,800mi thick. It is a highly viscous layer that lies beneath the crust. The mantle makes up 84% of the Earth's volume.

     The Earth's crust is what we, and all the other plants and animals live on. It lies right above the mantle. It occupies less than 1% of the earth's volume. It is made of a assortment of igneous, metamorphic, and sedimentary rocks. 71% of the surface is covered in water. The crust is about 30 miles thick on land and about 5 miles thick underwater.

     The atmosphere of the Earth is divided into 5 main parts. The troposphere of the Earth contains 21% free oxygen. It also contains 78% nitrogen, 0.9% argon, and 1% of carbon dioxide, water vapor, methane, and other gaseous molecules. The green house gasses in the atmosphere are mainly ozone, methane, water vapor, and carbon dioxide.   Above the troposphere is the stratosphere. The ozone layer is located here. It is important for life on Earth because it protects the surface from ultraviolet light. The mesosphere and thermosphere follow. Beyond these is the exosphere which leads into the magnetosphere. This is where the Earth's magnetic fields interact with the solar wind.