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| Quick Facts
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Mass (kg) : 5.98 x 10^24
Diameter (km) : 12756
Mean density (kg/m^3) : 5520
Escape velocity (m/sec) : 11200
Equatorial surface gravity (m/sec^2) : 9.78
Average distance from Sun (AU) : 1 (149,600,000 km)
Rotation period (length of day in Earth hours) : 23.93
Revolution period (length of year in Earth days) : 365.26
Mean orbital velocity (km/sec) : 29.79
Obliquity (tilt of axis in degrees) : 23.4
Orbit eccentricity (deviation from circular) : 0.017
Mean surface temperature (K) : 281 (15 degree Celsius)
Maximum surface temperature (K) : 310
Minimum surface temperature (K) : 260
Visual geometric albedo (reflectivity) : 0.39
Highest point on surface : Mount Everest (8+ km above sea-level)
Atmospheric components : 78% nitrogen, 21% oxygen, 1% argon
Surface materials : basaltic and granitic rock and altered materials
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| The Living Planet
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Earth is the only known planet in the solar system that supports life. Adequate supply of water and oxygen encouraged the growth of organism on this blue planet. From space, Earth is often identified by its distinct dark blue oceans, its brown and green landmasses and its snow white clouds.
Earth is the third planet from the Sun and lies at distance of 149,600,000 kilometers away from it (1 Astronomical Unit) and is ranked as the fifth largest planet in the Solar System with an average diameter of 12,756.3 km and a mass of 5.98 x 10^24 kg.
The earth and its satellite, the moon, also move together in an elliptical orbit about the sun. The eccentricity of the orbit is slight, so that the orbit is virtually a circle. The approximate length of the earth's orbit is 938,900,000 km (583,400,000 mi), and the earth travels along it at a velocity of about 106,000 km/hr (about 66,000 mph). Earth takes about 23 hours 56 minutes 4.1 seconds to complete a single rotation on its own axis and approximately 365.26 earthdays to finish its revolution around the sun. As the period of the earthıs revolution isnıt accurate in complete days, therefore we had a leap year every four years to count in the extra day.
Earthıs sphere is imperfect. It is slightly flatten at the poles and equatorial regions bulge out. Its shape somehow looked like a squashed orange. Accurate readings shown that the equatorial regions bulge out by 21 km; the North Pole bulge by 10 km; and the South Pole is depressed by 31 km.
In common with the entire solar system, the earth is moving through space at the rate of approximately 20.1 km/sec or 72,360 km/hr (approximately 12.5 mi/sec or 45,000 mph) toward the constellation of Hercules. The Milky Way galaxy as a whole, however, is moving toward the constellation Leo at about 600 km/sec (about 375 mi/sec).
Earthıs atmosphere composed mainly of nitrogen, which is harmless to the organisms living on Earth. This is one of the main reasons why Earth could harbour life. Venusıs atmosphere consisted mainly of carbon dioxide and while Uranusı atmosphere is dominated by ethane gas. Both gases are fatal to organisms if inhaled at great amounts. Furthermore, Earthıs atmosphere has a fair proportion of oxygen gas that organisms depended on for life.
71 percent of the Earthıs surface is covered by liquid water. Earthıs distance from the sun is such that water would not evaporate due to high heat like in Venus or freeze due to low temperatures like in Mars. Earthıs average global temperature is 20 degree Celsius, just right for water to exist in liquid state. Favourable conditions, like presence of water and oxygen, greatly accelerated the growth of organisms on Earth.
| Composition of Earth
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Earth is the densest planet in the solar system.
Earth is mainly divided in 5 distinct layers, each with individual seismic and chemical properties, mainly (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 Earthıs crust varies in thickness at different places. It is usually thinner under the oceans then under the continents. Only the inner core and the crust are solid, whereas all the other layers like mantle, outer core are in semi-molten state. Most of the mass of the Earth is contributed by the mantle and most of the rest by the core. The landmasses that we inhabited on contributed only a negligible mass towards the total mass.
The core is probably composed mostly of iron (or nickel/iron). Temperatures at the center of the core may be as high as 7500 K, hotter than the surface of the Sun. The lower mantle is probably mostly silicon, magnesium and oxygen with some iron, calcium and aluminum. The upper mantle is mostly olivene and pyroxene (iron/magnesium silicates), calcium and aluminum. We know most of this only from seismic techniques; samples from the upper mantle arrive at the surface, as lava from volcanoes but the majority of the Earth is inaccessible. The crust is primarily quartz (silicon dioxide) and other silicates like feldspar. Taken 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% Sulphur
0.05% Titanium
There are (at present) eight major plates:
North American Plate - North America, western North Atlantic and Greenland
South American Plate - South America and western South Atlantic
Antarctic Plate - Antarctica and the "Southern Ocean"
Eurasian Plate - eastern North Atlantic, Europe and Asia except for India
African Plate - Africa, eastern South Atlantic and western Indian Ocean
Indian-Australian Plate - India, Australia, New Zealand and most of Indian Ocean
Nazca Plate - eastern Pacific Ocean adjacent to South America
Pacific Plate - most of the Pacific Ocean (and the southern coast of California!)
There are also twenty or more small plates such as the Arabian, Cocos, and Philippine Plates. Earthquakes are much more common at the plate boundaries due to plate tectonics.
The Earth's surface is very young by astronomical standards. In the relatively short period of 500,000,000 years or so, erosion and tectonic processes destroyed and recreated most of the Earth's surface and thereby 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 that are older than 4 billion years old are rare. The oldest fossils of living organisms are less than 3.9 billion years old. Unfortunately, there is also no record of the critical period when life first appeared on the face of Earth.
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