Earth and Moon     EARTH     Earth and Moon

Located 149 600 000 kilometres (or 1.00 AU) from the sun is Earth. Being the fifth largest planet in the solar system it has a diameter of 12 756.3 kilometres. Weighing 5.972e24 kilograms, it is also the fifth heaviest planet- only being outweighed by Uranus, Neptune, Saturn and Jupiter.

More is known about Earth than any other planet (for obvious reasons!). Below is some information about Earth.

The Earth is divided into several layers which have distinct chemical and seismic properties.


Depth (km)Layer
0-40Crust
40-400Upper mantle
400-650Transition mantle
650-2700Lower mantle
2700-2890D'' layer
2890-5150Outer core
5150-6378Inner core


The crust will vary in thickness depending on it's position. The crust under the oceans tends to be thinner and that under the continents tends to be thicker. The inner core and crust are the two solid layers, while the outer core and mantle layers are plastic or semi-fluid. As a whole, the Earth's chemical composition (by mass) is:

34.6%Iron
29.5%Oxygen
15.2%Silicon
12.7%Magnesium
2.4%Nickel
1.9%Sulfur
0.05%Titanium


Water is a major element on Earth, as it covers 71% of the Earth. At the moment, Earth is the only planet on which water can exist in liquid form (though there may be liquid ethane or methane on Titan's surface and liquid water below the surface of Europa). The heat capacity of our oceans is also very important, as it keeps the Earth's temperature stable.

Currently, the Earth's atmosphere is 77% nitrogen, 21% oxygen. Signs of argon, carbon dioxide and water are also present. It is believed that there was a greater amount of carbon dioxide in the atmosphere when Earth was formed, but it has since been absorbed and incorporated into rocks, oceans and living planets. But the amount of carbon dioxide present in the atmosphere is also a major concern in maintaining the Earth's surface temperature. The greenhouse effect is what keeps the average surface temperature at about 35 degrees, otherwise life would not be present on earth, as the temperature would range from approximately -21C and +14C. But too large an amount of greenhouse gases could also mean that the surface temperature of Earth, resulting in the melting on the polar ice caps which could also have detrimental effects to life (flooding etc).

Earth has only one natural satellite, although there are many artificial satellites orbiting Earth providing us with telecommunication services- such as the Internet, overseas/long distance telephone calls, satellite television etc. This natural satellite is called the Moon. The Moon and the Earth have very interesting interactions and it is known now that the Moon slows the Earth's rotation by 2 milliseconds per century. Research has shown that about 900 million years ago, there were 18 hours in a day, and 481 days in a year.