Earth is the third planet from the Sun. It is the largest terrestrial planet and also the fifth largest planet. It also has the highest density out of the planets.


Earth is special due to its life-sustaining conditions. It has water (in three (solid, liquid, gas) of the four (solid, liquid, gas, plasma) states of matter) for living things to drink, an atmosphere so we can breathe and not have serious cancer. It actually has three moons: The Moon (aka Luna), 2016 HO3,[1] and Cruithne.[2] 2016 HO3 and Cruithne are «Quasi-satellites», which were found to technically orbit both the Sun and the Earth.


The structure of the Earth is divided into 5 layers: The lithosphere, which contains the crust and a small portion of the next layer, the asthenosphere, the rest of the mantle, the outer core, which generates the Earth's magnetic field that protects us from deadly solar rays, and the inner core.

Layer Name Depth (km) Temperature (oC)
Lithosphere (crust + upper asthenosphere) >8 (ocean)

>40 (crust)

35 to -14
Asthenosphere 200 1,300
Mantle 2,886 500 - 4,000
Outer Core 2,250 4,230
Inner Core 1,220 5,430


The Earth has an atmosphere that extends to 100 kilometers above the Earth's surface. Air referrers to any part of the atmosphere. 78% of the atmosphere is made out of Nitrogen, while 21% is made out of breathable oxygen. The remaining 1% is made out of other gases like hydrogen, helium, and argon. The layers of the atmosphere are:

  • Troposphere (6 - 20 km)
  • Stratosphere (50 km)
  • Mesosphere (85 km)
  • Thermosphere (690 km)
  • Exosphere (10,000 km)

Even though the thermosphere goes up to an altitude of 690 kilometers, the defined boundary between the atmosphere and space, called the Kármán line, is placed at an altitude of 100 kilometers.[3]

Magnetic Field


The Earth has a magnetic field to protect us from harmful solar rays. All magnets have a north pole and a south pole.[lower-alpha 1] The Earth's magnetic poles are slightly off-target, since the magnetic north pole is 2,000 km away from the geographical north pole and the south pole is located off the coast of Antarctica. Since opposite sides attract and like charges repel each other, the forces made by a pole would point toward the opposite pole! The inner core of the Earth is what generates the magnetic field, in other words, the inner core is a giant magnet.


  3. The 100 km Boundary for Astronautics by Dr. S. Sanz Fernández de Córdoba. Published by Fédération Aéronautique Internationale on 2004-06-24.


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