Earth

The earth is the third (3rd) planet from the sun in the solar system, Earth is both a terrestrial and aquatic world, with more than half of it covered by ocean. It’s the only world known to harbor life, of all existing planets, it is the most habitable . Earth’s atmosphere is rich in life-sustaining nitrogen and oxygen. Earth's surface rotates about its axis at 1,532 feet per second — slightly more than 1,000 mph — at the equator. The planet zips around the sun at more than 18 miles per second.
   

  Diameter: 7,926 miles (12,760 km)
 Orbit: 365.24 days
 Day: 23 hours, 56 minutes

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

Earth is the only planet with an English name. The name derives from Old English and Germanic. although There are, of course, hundreds of other names for the planet in other languages.It was not until the time of the sixteenth century that it was understood that the Earth is just one of 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. The crust varies considerably in thickness,. The inner core and crust are solid; the outer core and mantle layers are plastic or semi-fluid.
        The core is probably composed mostly of iron  though it is possible that some lighter elements may be present, too. Temperatures at the center of the core may be as high as 7500 K, hotter than the surface of the Sun. The lower rocks are probably mostly silicon, magnesium and oxygen with some iron, calcium and aluminum. The upper mantle is mostly olivine and pyroxene (iron/magnesium silicates), calcium and aluminum.  The earth crust is primarily composed of quartz (silicon dioxide) and other silicates like feldspar. Most of the mass of the Earth is in the mantle, most of the rest in the core; the part we inhabit is a tiny fraction of the whole (values below x10^24 kilograms):

atmosphere = 0.0000051
oceans = 0.0014
crust = 0.026
mantle = 4.043
outer core = 1.835
inner core = 0.09675