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Earth

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Earth

 

Diameter: 12,742 km
Age: 4.54 billion years
Distance from Sun: 149,600,000 km
Surface area: 510,072,000 k/m²
Length of day: 24 hours
Gravity: 9.78 m/s²
Circumference: 40,030 km
Mass: 5.972E24 kg
Length of year: 365 days
Surface temp: -88 to 58 C

Earth is the third planet from the Sun and the fifth largest.

Earth is the only planet whose English name doesn’t derive from  Greek/Roman mythology. The name comes from Old English and Germanic. There are also hundreds of other names for the planet in many languages.  In Roman Mythology, the goddess of the Earth was called Tellus – the fertile soil (Greek: Gaia,  terra mater – Mother Earth).

It was not until the time of Copernicus in the sixteenth century, that it was understood that the Earth is  just another planet.

Even thought Earth can be studied without the aid of spacecraft, it wasn’t until the twentieth century that we had maps of the entire planet.  Pictures of the planet taken from space were of considerable importance; they can help in weather prediction and especially in tracking and predicting hurricanes.

The Earth’s surface is very young, by astronomical standards, a period of 500,000,000 years of erosion and tectonic processes destroy and recreate most of  the Earth’s  surface. Which eliminate almost all traces of earlier geologic surface history such as impact craters.  Hence the very early  history of the Earth has mostly been erased.  The Earth is 4.5 to 4.6 billion years old,  but the oldest known rocks  are about  4 billion years old and rocks older than 3 billion years are very rare.  The oldest fossils of living organisms that have been found are less than 3.9 billion  years old. There is no record of the period when life was first beginning on the planet.

An estimated 71% of the Earth’s surface is covered with water.  Earth is the only planet in our solar system on which water can exist in liquid form on the surface. Liquid water is essential for life as we know it.  The heat capacity of the oceans is also help the Earth’s temperature remain relatively stable.  Liquid water is what causes for most of the erosion and weathering of  the Earth’s land masses, a process unique in the solar  system today.

Earth's atmosphere seen here at the limb

Earth’s atmosphere seen at the limb

The Earth’s atmosphere consists of 77%  nitrogen, 21% oxygen, with traces of argon, carbon dioxide  and H2O. Scientists believe a much larger amount of carbon dioxide existed in the Earth’s atmosphere when began but it has since been absorbed into the carbonate rocks and some dissolved into the oceans and also consumed by living plants. Plate tectonics plus biological processes now keep a continual flow of carbon  dioxide from the atmosphere to the various “sinks” and back again in an endless cycle. The very small amount of carbon  dioxide resident in the atmosphere at any time is very important to the stability of the Earth’s surface temperature by the greenhouse effect. The greenhouse effect raises the average surface temperature an estimated 35 degrees C above what it would otherwise be (eg: from a frigid -21 C to a comfortable  +14 C); without this effect the oceans would freeze and life as we know it would be impossible.

Earth from Apollo 11

View from Apollo 11

The existence of free oxygen is quite unique from a chemical point of view point. Oxygen is a very reactive gas and under normal circumstances it quickly combines with other elements.  The oxygen on Earth is produced by  biological processes’.

The gravitational forces of the Earth and Moon have slowed the Earth’s rotation by about 2 milliseconds per century. Currently researchers believe that in about 900 million years ago there will be 481 18-hour days  in a year.

Earth’s magnetic field is produced by electric currents in the outer core. The interaction of the solar wind combined with the Earth’s magnetic field causes the auroras in Earth’s upper atmosphere. Irregularities in these forces cause the magnetic poles to shift, and can even reverse relative to the surface. The corrent geomagnetic north  pole is currently located in northern Canada.

Earth’s magnetic field interacts with the solar wind which produce the Van Allen radiation belts, two doughnut shaped rings of ionized gas or plasma, are trapped in orbit around the Earth. The outer belt  stretches from 19,000 km in altitude to 41,000 km; the inner belt is between  13,000 km and 7,600 km in altitude.

Earth’s Satellite

Earth has only one natural satellite, the Moon.

 

 

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