Earth
From Wikipedia, the free encyclopedia
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| Designations | |
|---|---|
| Alternative names | Blue Planet, Terra, Planet Earth |
| Orbital characteristics Epoch J2000.0 |
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| Aphelion | 152,097,701 km 1.0167103335 AU |
| Perihelion | 147,098,074 km 0.9832898912 AU |
| Semi-major axis | 149,597,887.5 km 1.0000001124 AU |
| Eccentricity | 0.016710219 |
| Orbital period | 365.256366 days 1.0000175 yr |
| Average orbital speed | 29.783 km/s 107,218 km/h |
| Inclination | 1°34'43.3" to Invariable plane |
| Physical characteristics | |
Earth is the third planet from the Sun. It is one of the four terrestrial planets in our Solar System. This means most of its mass is solid. The other three are Mercury, Venus and Mars. The Earth is also called Planet Earth, Blue Planet[note 1] and Terra.[note 2]
Earth is home to millions of species of plants and animals,[1] including humans. Earth is the only place in the universe where life has been confirmed to exist.[2] Science shows that the Earth formed around 4.5 billion years ago.[3][4] The things that live on Earth have completely changed its air or atmosphere. This is called a biosphere.[5]
About 71% of Earth's surface is covered in salt water oceans. Earth is the only place in the universe where liquid water is known to exist.[6] The other 29% is made of rocky land in the shape of continents and islands. Earth interacts with other objects in the Solar System, particularly the Sun and the Moon. The Earth orbits or goes around the Sun roughly once every 365.25 days. One spin is called a day and one orbit around the Sun is called a year. This is why we have 365 days in year. Earth has only one moon, known as the Moon.
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[change] History
- See also: Creation myth
Most scientists think that the Earth and the other planets formed about 4.5 billion years ago.[3] They were made of the leftover gas from the nebula that made the Sun. Some scientists think that the Moon might have been made from part of a small planet which is sometimes called Theia. Scientists believe that it crashed into Earth a part broke off — becoming the Moon.[7]
Condensing water vapour or steam, comets and asteroids hiting the Earth made the oceans. Within a billion years (that is at about 3.8 billion years ago) the first life evolved.[8] Some life developed photosynthesis which lets plants make food from the Sun's light and water. This released a lot of oxygen into the atmosphere or air, making the Earth's surface suitable for life. This oxygen also formed the ozone layer which protects the Earth from bad ultraviolet radiation from the Sun. This protection made it possible for things to move from the deep ocean to the surface. Long ago almost all land was in one place. This is called a supercontinent. The earliest known supercontinent was called Rodina. Scientists think that soon after this there was a time when the Earth was almost entirely covered by thick ice sheets called glaciers.[9] This is called Snowball Earth theory.[9]
[change] What it is made of
Earth is a terrestrial planet. This means it is made up of solid rock unlike a gas giant such as Jupiter. It is the largest out of the four terrestrial planets in mass and diameter. Earth also has the strongest gravitational and magnetic field.
[change] Shape
The Earth's shape is an oblate spheroid. This means it is basically a sphere but it bulges around the middle. The circumference of the Earth is about 40,000 kilometers; the average width of the Earth is about 12,700 km. The highest point on Earth is the peak of Mount Everest at 8,848 m above sea level. The lowest natural point is the bottom of the Mariana Trench at 10,911 meters below sea level. Because of the bulge at the middle or the equator, the farthest point from the Earth's center is the top of Mount Chimborazo in Ecuador.[10]
[change] Internal structure
Inside, the Earth is similar to the other terrestrial planets. It has an outer, solid rock layer called the crust. Everything that lives on Earth is on top of the crust. Below that is a layer of thick, liquid rock called the mantle. Under that is a thin liquid layer called the outer core and then the solid iron inner core. The thickness of the crust changes. On land the average is between 30–50 kilometers thick. Under the oceans in some places it is only 6 kilometers thick.[11] The inside of the Earth is very hot, the temperature of the outer core may be as high as 7,000 degrees Celsius.[12]
[change] Tectonic plates
The Earth is the only terrestrial planet with active plate tectonics.[13] Due to plate tectonics the Earth's crust basically floats on the thick liquid rock of the mantle below.[14] The crust is split up into parts called plates. These plates interact as they move about causing earthquakes and creating volcanoes and mountain ranges. The place where plates meet are called plate boundaries. There are three types of plate boundary: constructive, destructive and transform.[13][15][16]
- At a constructive plate boundary two plates move away from each other, and hot magma (liquid rock) is pushed upwards through the cracks. These kinds of boundaries make ocean rifts, undersea volcanoes or ridges. An example of this kind of plate boundary is the island of Hawaii.[15]
- At a destructive plate boundary, two plates move towards each other. This forms islands, volcanoes and high mountain ranges. The Himalayas were made by this process.[15]
- At a transform plate boundary, two plates move parallel to each other. As they move the grind against each other. This kind of plate boundary causes earthquakes.[16]
[change] Surface
The Earth changes greatly from place to place. Over 70% of the Earth surface is covered by water.[17] The underwater surface has many of the same features as the above sea with volcanos, mountains and trenches or canyons. The 30% not covered by water is mostly forests, deserts, plains, mountains and plateaux. Human civilisation has led to increasing urbanisation — the growth of cities.
Many things can change the surface of the Earth. Plate tectonics is main cause of change but there are others such as erosion from wind and rain, erosion by the oceans or meteorite impacts. There are three main types of rock that make up the Earth's surface:
- Igneous rock is made when magma or lava from the mantle reaches the surface and cools. As it gets colder it turns into rock or solidifies.
- Sedimentary rock is made from sediment, like sand or small bits of other rock, that has been crushed and packed tightly together.
- Metamorphic rock which is made when either of the other two types are changed by high or low temperatures and pressures.
[change] Hydrosphere
All the water on Earth, on land or in the atmosphere, is part of the hydrosphere. No other planet, that humans know of has a hydrosphere. About 97.5% of all water is salt water. About half the fresh water is currently ice.[18] The oceans absorb or soak up carbon dioxide, a gas that adds to the greenhouse effect and global warming.
[change] Atmosphere
A planet's atmosphere is a layer of different gases surrounding it. It is kept there by gravity. The Earth's atmosphere is made of roughly 78% nitrogen, 21% oxygen and small amounts of other gases.[19] This mixture is often called air. Further up there is a layer of ozone gas called the Ozone layer. Ozone absorbs ultraviolet radiation from the Sun. Ultraviolet radiation is dangerous to people, so without the Ozone layer life would not be possible. The atmosphere also protects the earth from crashes with meteors and small asteroids. This is because they burn up due to all the friction as they fly through it. It also helps to keep Earth warm. Some gases including carbon dioxide and methane act like a blanket around the Earth, they trap heat under them, keeping the Earth warm. This is called the natural greenhouse effect.[20] When humans build factories and power plants to make electricity, combustion is involved. Combustion lets out a lot of carbon dioxide. This carbon dioxide goes up into the atmosphere and traps more heat. This is called global warming.
[change] Weather, climate, and water cycle
Hot air rises. As it rises it gets colder again and falls. This is called convection currents.[21] When hot air meets cold air different weather effects happen. Convection currents are the cause of almost all weather on Earth. When it gets hot on the surface water evaporates and becomes steam or water vapour. This hot water vapour rises. As it rises it gets colder. When gets cold enough it turns back into water again. This causes the clouds and rain. It is called the water cycle.[21]
[change] Orbit and rotation
The Earth takes about 24 hours to complete one day and 365 days to complete an year. The Earth is, on average, 150 million miles away from the Sun, and moving at a speed of 30 kilometers a second or 108,000 miles an hour.[22]
The Moon orbits the Earth at an average distance of 250,000 miles. It is tidally locked to Earth, which means it always has the same side facing the Earth. It takes roughly one month to complete one orbit.
The Earth is part of the Solar System and orbits the sun along with thousands of small objects and eight planets. The Sun and therefore the Solar System are currently traveling through the Orion Arm of the Milky Way Galaxy and will be for approximately the next 10,000 years.[23]
[change] Notes
- ↑ Blue Planet is used as the title of several films Blue Planet and The Blue Planet, in the Life issue The Incredible Year '68 featuring the Earthrise photograph with lines from poet James Dickey Behold/The blue planet steeped in its dream/Of reality [1] pp. 7–8 [2], and in the title of the European Space Agency bulletin report Exploring the water cycle of the 'Blue Planet' [3]
- ↑ Note that by International Astronomical Union convention, the term "Terra" is used for naming extensive land masses, rather than for the planet Earth. Cf. Blue, Jennifer (July 5, 2007). Descriptor Terms (Feature Types). Gazetteer of Planetary Nomenclature. USGS. Retrieved on 5 July 2007.
[change] References
- ↑ How Many Species are There on Earth. Harvard University. Retrieved on 28 July 2009.
- ↑ BBC : The Earth. BBC. Retrieved on 28 July 2009.
- ↑ 3.0 3.1 The age of the Earth in the twentieth century- a problem (mostly) solved. Geological Society, London, Special Publications. Retrieved on 28 July 2009.
- ↑ History of earth. Microsoft. Retrieved on 28 July 2009.
- ↑ Origins of life on Earth. Space.com. Retrieved on 28 July 2009.
- ↑ Rover reveals Mars was once wet enough for life. Microsoft. Retrieved on 28 July 2009.
- ↑ Origin of the Moon in a giant impact near the end of the Earth's formation. Nature.com. Retrieved on 28 July 2009.
- ↑ Earth Life Appeared on Land 1.5 billion Years Earlier Than Previously Thought. SpaceRef.com. Retrieved on 3 July 2009.
- ↑ 9.0 9.1 The Snowball Earth. Paul F. Hoffman and Daniel P. Schrag. Harvard University. Retrieved on 28 July 2009.
- ↑ Did Edmund Hillary Climb the Wrong Mountain?. Professional Surveyor Magazine. Retrieved on 6 August 2009.
- ↑ Toshiro Tanimoto. Crustal Surface of the Earth. American Geophysical Union. Retrieved on 2 August 2009.
- ↑ D. Alfé; M. J. Gillan, L. Vočadlo, J. Brodholt, G. D. Price (2002-04-25). The ab initio simulation of the Earth’s core. D. Alfé. Retrieved on 2 August 2009.
- ↑ 13.0 13.1 Tackley, Paul J. (2000-06-16). "Mantle Convection and Plate Tectonics: Toward an Integrated Physical and Chemical Theory". Science 288 (5473): 2002–2007. DOI:10.1126/science.288.5473.2002.
- ↑ The Crust. Oregon State University. Retrieved on 3 July 2009.
- ↑ 15.0 15.1 15.2 Seyfert, Carl K. (1987). The Encyclopedia of Structural Geology and Plate Tectonics. ISBN 9780442281250.
- ↑ 16.0 16.1 Oreskes (2003). Plate Tectonics : An Insider's History of the Modern Theory of the Earth. Westview Press. ISBN 9780813341329.
- ↑ CHAPTER 8: Introduction to the Hydrosphere. Physical Geography. Retrieved on 6 August 2009.
- ↑ WORLD WATER RESOURCES AND THEIR USES. UNESCO. Retrieved on 6 August 2009.
- ↑ NASA - Earth's atmosphere. NASA. Retrieved on 6 August 2009.
- ↑ Fundamentals of physical geography - the greenhouse effect. Physical Geography. Retrieved on 6 August 2009.
- ↑ 21.0 21.1 What causes weather?. NASA. Retrieved on 6 August 2009.
- ↑ NASA- an Earth fact sheet. NASA. Retrieved on 6 August 2009.
- ↑ Earth's location in the Milky Way. NASA. Retrieved on 6 August 2009.
[change] Other pages
[change] Other websites
- Solar Views. Calvin J. Hamilton. Retrieved on 6 August 2009.
- NASA – Earth. Nasa. Retrieved on 6 August 2009.
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