Earth

Earth

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Earth is the only planet whose name does not derive from Roman/Greek mythology. The name Earth arrives from Old English and Germanic. There are hundreds of other names for the planet in other languages. In roman mythology was the goddess of the Earth, Tellus, the fertile soil. Greek: Gaia, terra mater, Mother Earth.

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

Earth is the third planet from the sun and the fifth largest.
                           diameter: 12.756.3 km
                                mass: 1
                                 orbit: 149.600.000 km or 1 AU from the Sun

The earth can of course be studied without the aid of a satellites. But it was not until the twentieth century that we had maps of the entire planet. Pictures, taken from space, are of considerable importance. For example, they are almost indispensable help in weather forecasts and especially in tracking and predicting hurricanes. And they are remarkably beautiful.

The Earth is divided into seven layers which have distinct chemical and seismic properties, here below are these layers in right order. (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

The crust varies considerably in thickness, it is of course thinner in the oceans, and thicker under the continents. The crust and the inner core are solid. The mantle and the outer core layers are plastic or semi-fluid. The various layers are separated by discontinuities which are evident in seismic data. The best known is the Mohorovicic between the upper mantle and the crust.

The highest point of Earth is Mount Everest, which rises 8848 meters from sea level. The lowest point of Earth is in the pacific ocean, it is Challenger rift 11034 meters deep!!

The core is probably composed mostly of iron though it is possible that some lighter elements may be present too. The temperature at the core is probably as hot as the surface of the Sun, or about 6000°C. The lower mantle is mostly composed by silicon, magnesium, oxygen with some iron, aluminium and calcium. The upper mantle is mostly olivine and pyroxene, aluminium and calcium. Samples of these matters arrive from volcanic lava but the majority of the Earth is inaccessible. Lets look at the Earth´s chemical composition by mass.

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

The Earth is the densest major body in the solar system

Unlike the other terrestrial planets is Earth´s crust divided into several separate solid plates which float around independently on the top of the mantle. This is known as Plate Tectonics. It is characterised by two major processes: Spreading and Subduction. Subduction occurs when two plates collide and the edge of one dives beneath the other and ends up being destroyed in the mantle, we feel it as an earthquake. Spreading occurs when two plates move from each other and new crust is created by upwelling magma from below, we see it as an volcanic eruption. There are now eight major plates.

North America Plate
South America Plate
Antarctic Plate
Eurasian Plate
African Plate
Indian Australian Plate
Nazca Plate
Pacific Plate

The surface of Earth is very young. In the relatively short period of 500.000.000 years or so erosion and tectonic processes destroy and recreate most of its surface. Thus the very early history of the Earth has mostly been erased.

The Earth is about 4.6 to 4.7 billion years old. The oldest known rocks are about 4 billion years old. The oldest fossils of living organisms are less than 3.9 billion years old. There is no record of the critical period when life was getting started. (The cosmic calendar)

71% of Earth´s surface is covered with water, the rest is dry land.

The Earth is the only planet in the solar system that water exists in liquid form. Liquid water is essential for life as we know it. The heat capacity of the oceans is also very important in keeping the Earth´s temperature relatively stable. Water is also responsible for most of the erosion and weathering of the Earth´s contents. This process is very unique in the solar system today. It might have occurred on Mars in the past.

The Earth´s atmosphere is 77% nitrogen, 21% oxygen, traces of argon, carbon dioxide and water.

The presence of free oxygen is quite remarkable from a chemical point of view. Oxygen is ver reactive gas and under normal circumstances would quickly combine with other elements. The oxygen in Earth´s atmosphere is produced and maintained by biological process. Without life there would be no free oxygen.

Earth has one natural satellite the Moon, but thousands of small artificial satellites have been placed around the Earth.

The interaction of the Earth and the Moon slows the rotation of Earth down by about 2 milliseconds per century.

Earth has modest magnetic field produced by electric currents in the core. The solar winds, the Earth´s magnetic field and the Earth´s upper atmosphere causes the Auroras. Irregularities in these factors cause the magnetic poles to move relatively to the surface; the north magnetic pole is currently located in northern Canada.