Earth is the planet we live on. It is the third planet from the Sun. It is the only planet known to have life on it. The Earth formed around 4.5 billion years ago. It is one of four rocky planets on the inside of the Solar System. The other three are Mercury, Venus, and Mars.
(94500000 mi; 1.017 AU)
(91401000 mi; 0.98327 AU)
(92955902 mi; 1.00000102 AU)
Average orbital speed
(107200 km/h; 66600 mph)
|−11.26064° to J2000 ecliptic|
|6371.0 km (3958.8 mi)|
|6378.1 km (3963.2 mi)|
|6356.8 km (3949.9 mi)|
|Volume||1.08321×1012 km3 (2.59876×1011 cu mi)|
|Mass||5.97237×1024 kg (1.31668×1025 lb) |
|5.514 g/cm3 (0.1992 lb/cu in)|
|9.807 m/s2 (1 g; 32.18 ft/s2)|
|11.186 km/s |
(40270 km/h; 25020 mph)
Sidereal rotation period
(23h 56m 4.100s)
Equatorial rotation velocity
|0.4651 km/s |
(1674.4 km/h; 1040.4 mph)
|101.325 kPa (at MSL)|
|Composition by volume|
The large mass of the Sun makes Earth move around it, just as the mass of Earth makes the moon move around it. Earth also turns around in space, so that different parts face the Sun at different times. Earth goes around the Sun once (one year) for every 3651⁄4 times it turns around (one day).
Earth is the only planet in our solar system that has a large amount of liquid water. About 74% of the surface of Earth is covered by liquid or frozen water. Because of this, people sometimes call it the blue planet.
Because of its water, Earth is home to millions of species of plants and animals. The things that live on Earth have changed its surface greatly. For example, early cyanobacteria changed the air and gave it oxygen. The living part of Earth's surface is called the "biosphere".
Orbit and turningEdit
Earth is part of the eight planets and many thousands of small bodies that move around the Sun as its solar system. The Solar System is moving through the Orion Arm of the Milky Way galaxy now, and will be for about the next 10,000 years.
Earth is about 150,000,000 kilometres or 93,000,000 miles away from the Sun (this distance is called an "Astronomical Unit"). It moves on its orbit at an average speed of about 30 km/s (19 mi/s). Earth turns all the way around about 3651⁄4 times in the time it takes for Earth to go all the way around the Sun. To make up this extra bit of a day every year, an additional day is used every four years. This is named a "leap year".
The Moon goes around Earth at an average distance of 400,000 kilometres or 250,000 miles. It is locked to Earth, so that it always has the same half facing Earth; the other half is called the "dark side of the moon". It takes about 271⁄3 days for the Moon to go all the way around Earth, but because Earth is moving around the Sun at the same time, it takes about 291⁄2 days for the Moon to go from dark to bright to dark again. This is where the word "month" came from, even though most months now have 30 or 31 days.
History of EarthEdit
- See also: Historical geology, Age of the Earth, Giant impact hypothesis, and Great Oxygenation Event
Earth and the other planets formed about 4.6 billion years ago. They were made of the leftover gas from the nebula that made the Sun. The Moon may have been formed after a collision between the early Earth and a smaller planet (sometimes called Theia). Scientists believe that parts of both planets broke off — becoming (by gravity) the Moon.
Earth's water came from different places. Condensing water vapour, and comets and asteroids hitting Earth, made the oceans. Within a billion years (that is at about 3.6 billion years ago) the first life evolved, in the Archaean era. Some bacteria developed photosynthesis, which lets plants make food from the Sun's light and water. This released a lot of oxygen, which was first taken up by iron in solution. Eventually, free oxygen got into the atmosphere or air, making Earth's surface suitable for aerobic life (see Great Oxygenation Event). This oxygen also formed the ozone layer which protects Earth's surface from bad ultraviolet radiation from the Sun. Complex life on the surface of the land did not exist before the ozone layer.
Earth's land and climate has been very different in the past. About 3 to 3.5 million years ago almost all land was in one place. This is called a supercontinent. The earliest known supercontinent was called Vaalbara. Much later, there was a time (the Cryogenian) when Earth was almost entirely covered by thick ice sheets (glaciers). This is discussed as the Snowball Earth theory.
What it is made ofEdit
Overall, Earth is made of iron (32.1%), oxygen (30.1%), silicon (15.1%), magnesium (13.9%), sulfur (2.9%), nickel (1.8%), calcium (1.5%), and aluminium (1.4%). The 1.2% left over is made of many different kinds of other chemicals. Chemicals that are very uncommon (such as gold and platinum) can be very valuable.
The structure of Earth changes from the inside to the outside. The center of earth (Earth's core) is mostly iron (88.8%), nickel (5.8%), sulfur (4.5%), and less than 1% other things. The Earth's crust is largely oxygen (47%). Oxygen is normally a gas but it can join with other chemicals to make compounds like water and rocks. 99.22% of rocks have oxygen in them. The most common oxygen-having rocks are silica (made with silicon), alumina (made with aluminium), rust (made with iron), lime (made with calcium), magnesia (made with magnesium), potash (made with potassium), and sodium oxide, and there are others as well.
Earth's shape is a spheroid: not quite a sphere because it is slightly squashed on the top and bottom. The shape is called an oblate spheroid. As Earth spins around itself, the centrifugal force forces the equator out a little and pulls the poles in a little. The equator, around the middle of Earth's surface, is about 40,075 kilometers or 24,900 miles long.
The highest mountain above sea level—the well-known Mount Everest (which is 8,848 metres or 29,029 feet above sea level)—is not actually the one that is the farthest away from the center of the Earth. Instead, the sleeping volcano Mount Chimborazo in Ecuador is; it is only 6,263 metres or 20,548 feet above sea level but it is almost at the equator. Because of this, Mount Chimborazo is 6,384 kilometres or 3,967 miles from the center of the Earth, while Mount Everest is 2 kilometres or 1.2 miles closer to it. Similarly, the lowest point below sea level that we are conscious of is the Challenger Deep in the Mariana Trench in the Pacific Ocean. It is about 10,971 metres or 35,994 feet below sea level, but, again, there are probably places at the bottom of the Arctic Ocean that are nearer to the center of the Earth.
What it is like insideEdit
The deepest hole ever dug is only about 12.3 kilometers or 7.6 miles. We know something about the inside of the Earth, though, because we can learn things from earthquakes and the times when volcanoes erupt. We are able to see how quickly the shock waves move through Earth in different places.
The inside of Earth is very different from the outside. Almost all of Earth's liquid water is in the seas or close to the surface. The surface also has a lot of oxygen, which comes from plants. Small and simple kinds of life can live far under the surface, but animals and plants only live on the surface or in the seas. The rocks on the surface of Earth (Earth's crust) are well known. They are thicker where there is land, between 30 to 50 km or 19 to 31 mi thick. Under the seas they are sometimes only 6 km or 3.7 mi thick. There are three groups of rocks that make up most of the Earth's crust. Some rock is made when the hot liquid rock comes from inside the earth (igneous rocks); another type of rock is made when sediment is laid down, usually under the sea (sedimentary rocks); and a third kind of rock is made when the other two are changed by very high temperature or pressure (metamorphic rocks). A very few rocks also fall out of the sky (meteorites).
Below the crust is warm and almost-liquid rock that is always moving around (the Earth's mantle). Then, there is a thin liquid layer of heated rock (the outer core). This is very hot: 7,000 °C or 13,000 °F or 7,300 K. The middle of the inside of the Earth would be liquid as well but all the weight of the rock above it pushes it back into being solid. This solid middle part (the inner core) is almost all iron. This is what makes the Earth magnetic.
Pieces of the crust form platesEdit
The Earth's crust is solid but made of parts which move very slowly. The thin level of hard rock on the outside of the Earth rests on hot liquid material below it in the deeper mantle. This liquid material moves because it gets heat from the hot center of the earth. The slow movement of the plates is what causes earthquakes, volcanoes and large groups of mountains on the Earth.
There are three ways plates can come together. Two plates can move towards each other ("convergent" plate edges). This can form islands (such as Japan), volcanoes, and high mountain ranges (such as the Andes and Himalayas). Two plates can move away from each other ("divergent" plate edges). This gives the warm liquid rock inside the earth a place to come out. This makes special mountain ranges below the sea or large low lands like Africa's Great Rift Valley. Plates are able to move beside each other as well ("transform" plate edges, such as the San Andreas Fault). This makes their edges crush against each other and makes many shocks as they move.
The outside of the Earth is not even. There are high places called mountains, and high flat places called plateaus. There are low places called valleys and canyons. For the most part, moving air and water from the sky and seas damages rocks in high places and breaks them into small pieces. The air and water then move these pieces to lower places. Because of this, the Earth would have been very flat a long time before now. The fundamental cause of the differences in the Earth's surface is plate tectonics. The shape of the entire planet itself is not even a ball. Because of its velocity, Earth has a slight bulge at the Equator. Other than that, Earth is shaped more like a pear than an actual sphere.
All places on Earth are made of, or are on top of, rocks. The outside of the Earth is usually not uncovered rock. Over 70% of the Earth is covered by seas full of salty water. This salty water makes up about 971⁄2% of all Earth's water. The fresh water people can drink is mostly ice. Only a very small amount is in rivers and under the Earth for people to drink and use. The air above the Earth stops the water from going away into outer space. Also, much of the land on Earth is covered with plants, or with what is left from earlier living things. Places with very little rain are dry wastes called deserts. Deserts usually have few living things, but life is able to grow very quickly when these wastes have rainfall. Places with large amounts of rain may be large woods. Lately, people have changed the environment of the Earth a great deal.
All around the Earth is a large amount of air (the atmosphere). The mass of the Earth pulls the gasses in the air down and does not let them go into outer space. The air is mostly made of nitrogen (about 78%) and oxygen (about 21%) but there are a few other gasses as well. Most living things need the air (or parts of the air gripped in the water) to breathe and live. They use the gasses—especially oxygen and carbon dioxide—to make and use sugar and to give themselves power.
The air animals and plants use to live is only the first level of the air around the Earth (the troposphere). The day to day changes in this level of air are named weather; the changes between places far away from each other and from year to year are named the climate. Rain and storms are both in this level. Both come about because this part of the air gets colder as it goes up. Cold air becomes thicker and falls, and warm air becomes thinner and goes up. The turning Earth moves the air as well and air moves north and south because the middle of the Earth generally gets more power from the Sun and is warmer than the north and south points. At the same time, air over water (specially very warm water) gets water in it but, because cold air is not able to take in as much water, it starts to make clouds and rain as it gets colder. The way water moves around in a circle like this is called the water cycle.
Above this first level, there are four other levels. The air gets colder as it goes up in the first level; in the second level (the stratosphere), the air gets warmer as it goes up. This level has a special kind of oxygen called ozone. The ozone in this air keeps living things safe from damaging rays from the Sun. The power from these rays is what makes this level warmer and warmer. The middle level (the mesosphere) gets colder and colder with height; the fourth level (the thermosphere) gets warmer and warmer; and the last level (the exosphere) is almost outer space and has very little air at all. It reaches about half the way to the Moon. The three outer levels have a lot of electric power moving through them; this is called the ionosphere and is important for radio and other electric waves in the air. It is also where the Northern Lights are.
Even though air seems very light, the weight of all of the air above the outside of the Earth (air pressure) is important. Generally, from sea level to the top of the outer level of the air, a space of air one cm2 across has a mass of about 1.03 kg and a space of air one sq in across has a weight of about 14.7 lb. The mass of the air also keeps the Earth safe when rocks (meteorites) hit it from outer space. Without the air, the damage meteorites do would be much greater. Because of the air, meteorites generally burn up long before they get to the earth.
The air also keeps the Earth warm, specially the half turned away from the Sun. Some gasses – especially methane and carbon dioxide – work like a blanket to keep things warm. In the past, the Earth has been much warmer and much colder than it is now. Since people have grown used to the heat we have now, though, we do not want the Earth to be too much warmer or colder. Most of the ways people create electric power use burning kinds of carbon—especially coal, oil, and natural gas. Burning these creates new carbon dioxide and can cause more warming. A large discussion is going on now about what people should do about the Earth's latest warming, which has gone on for about 150 years. So far, this warming has been good for people: plants have grown better and the weather has been better than when it was colder before. Some people who learn about science, though, say that many bad things will possibly come about if the warming goes on.
About seven billion people live on Earth. They live in about 200 different lands called countries. Some, for example, Russia, are large with many large cities. Others, for example, Vatican City, are small. The five countries with the most people are China, India, the United States, Indonesia, and Brazil. About 90% of people live in the north half of the world, which has most of the land. Scientists think that people originally came from Africa. Now, 70% of all people do not live in Africa but in Europe and Asia.
People change the Earth in many ways. They have been able to grow plants for food and clothes for about ten thousand years. When there was enough food, they were able to build towns and cities. Near these places, men and women were able to change rivers, bring water to farms, and stop floods (rising water) from coming over their land. People found useful animals and bred them so they were easier to keep.
- All astronomical quantities vary, both secularly and periodically. The quantities given are the values at the instant J2000.0 of the secular variation, ignoring all periodic variations.
- aphelion = a × (1 + e); perihelion = a × (1 – e), where a is the semi-major axis and e is the eccentricity. The difference between Earth's perihelion and aphelion is 5 million kilometers.
- Simon, J.L.; Bretagnon, P.; Chapront, J.; Chapront-Touzé, M.; Francou, G.; Laskar, J. (February 1994). "Numerical expressions for precession formulae and mean elements for the Moon and planets". Astronomy and Astrophysics 282 (2): 663–83.
- Staff (7 August 2007). "Useful Constants". International Earth Rotation and Reference Systems Service. Retrieved 23 September 2008.
- Williams, David R. (16 March 2017). "Earth Fact Sheet". NASA/Goddard Space Flight Center. Retrieved 26 July 2018.
- Allen, Clabon Walter; Cox, Arthur N. (2000). Allen's Astrophysical Quantities. Springer. p. 294. ISBN 978-0-387-98746-0. Retrieved 13 March 2011.
- "UCS Satellite Database". Nuclear Weapons & Global Security. Union of Concerned Scientists. 10 August 2018. Retrieved 27 September 2018.
- As of 4 January 2018, the United States Strategic Command tracked a total of 18,835 artificial objects, mostly debris. See: Anz-Meador, Phillip; Shoots, Debi, eds. (February 2018). "Satellite Box Score". Orbital Debris Quarterly News 22 (1): 12. https://orbitaldebris.jsc.nasa.gov/quarterly-news/pdfs/odqnv22i1.pdf. Retrieved 18 April 2018.
- Lide, David R. (2000). David R. Lide (ed.). Handbook of Chemistry and Physics (81st ed.). CRC. ISBN 978-0-8493-0481-1.
- "Selected Astronomical Constants, 2011". The Astronomical Almanac. Archived from the original on 26 August 2013. Retrieved 25 February 2011.
- World Geodetic System (WGS-84). Available online from National Geospatial-Intelligence Agency.
- International Earth Rotation and Reference Systems Service (IERS) Working Group (2004). "General Definitions and Numerical Standards" (PDF). In McCarthy, Dennis D.; Petit, Gérard (eds.). IERS Conventions (2003 (PDF). IERS Technical Note No. 32. Dennis D. McCarthy, Gérard Petit, IERS Convertions Centre. Frankfurt am Main: Verlag des Bundesamts für Kartographie und Geodäsie. p. 12. ISBN 978-3-89888-884-4. Retrieved 29 April 2016.
- Humerfelt, Sigurd (26 October 2010). "How WGS 84 defines Earth". Archived from the original on 24 April 2011. Retrieved 29 April 2011.
- Earth's circumference is almost exactly 40,000 km because the metre was calibrated on this measurement—more specifically, 1/10-millionth of the distance between the poles and the equator.
- Pidwirny, Michael (2 February 2006). Surface area of our planet covered by oceans and continents.(Table 8o-1). University of British Columbia, Okanagan. http://www.physicalgeography.net/fundamentals/8o.html. Retrieved 26 November 2007.
- Staff (24 July 2008). "World". The World Factbook. Central Intelligence Agency. Retrieved 5 August 2008.
- Due to natural fluctuations, ambiguities surrounding ice shelves, and mapping conventions for vertical datums, exact values for land and ocean coverage are not meaningful. Based on data from the Vector Map and Global Landcover datasets, extreme values for coverage of lakes and streams are 0.6% and 1.0% of Earth's surface. The ice shields of Antarctica and Greenland are counted as land, even though much of the rock that supports them lies below sea level.
- Luzum, Brian; Capitaine, Nicole; Fienga, Agnès; Folkner, William; Fukushima, Toshio et al. (August 2011). "The IAU 2009 system of astronomical constants: The report of the IAU working group on numerical standards for Fundamental Astronomy". Celestial Mechanics and Dynamical Astronomy 110 (4): 293–304. doi:10.1007/s10569-011-9352-4.
- The international system of units (SI) (PDF) (2008 ed.). United States Department of Commerce, National Institute of Standards and Technology Special Publication 330. p. 52.
- Williams, James G. (1994). "Contributions to the Earth's obliquity rate, precession, and nutation". The Astronomical Journal 108: 711. doi:10.1086/117108. ISSN 0004-6256.
- Allen, Clabon Walter; Cox, Arthur N. (2000). Allen's Astrophysical Quantities. Springer. p. 296. ISBN 978-0-387-98746-0. Retrieved 17 August 2010.
- Allen, Clabon Walter; Cox, Arthur N. (2000). Arthur N. Cox (ed.). Allen's Astrophysical Quantities (4th ed.). New York: AIP Press. p. 244. ISBN 978-0-387-98746-0. Retrieved 17 August 2010.
- "World: Lowest Temperature". WMO Weather and Climate Extremes Archive. Arizona State University. Archived from the original on 16 June 2010. Retrieved 7 August 2010.
- Kinver, Mark (10 December 2009). "Global average temperature may hit record level in 2010". BBC. Retrieved 22 April 2010.
- "World: Highest Temperature". WMO Weather and Climate Extremes Archive. Arizona State University. Archived from the original on 4 January 2013. Retrieved 7 August 2010.
- "Trends in Atmospheric Carbon Dioxide: Recent Global CO
2 Trend". Earth System Research Laboratory. National Oceanic and Atmospheric Administration. 26 July 2018. Archived from the original on 26 July 2018.
- "The age of the Earth in the twentieth century- a problem (mostly) solved". Geological Society, London, Special Publications. Retrieved 28 July 2009.
- Dalrymple G. Brent 2004. Ancient Earth, ancient skies: the age of Earth and its cosmic surroundings. Stanford. p26, table 3.1
- "Rover reveals Mars was once wet enough for life". Microsoft. Retrieved 28 July 2009.
- Blue Planet is a poetic title for the Earth used in movies, in cheap paper books, in poetry, and in government reports (such as the European Space Agency's Exploring the water cycle of the Blue Planet)
- "How many species are there on Earth". Harvard University. Retrieved 28 July 2009.
- Purves, William Kirkwood (2001). Life, the science of biology. Macmillan. p. 455. ISBN 978-0-7167-3873-2.
- "Origins of life on Earth". Space.com. Retrieved 28 July 2009.
- "Earth's location in the Milky Way". NASA. Retrieved 6 August 2009.
- Forbes: How fast does the Earth move through the universe?
- "NASA- an Earth fact sheet". NASA. Retrieved 6 August 2009.
- Dalrymple, G. Brent (2001). "The age of the Earth in the twentieth century: a problem (mostly) solved". Special Publications, Geological Society of London 190 (1): 205–221. doi:10.1144/GSL.SP.2001.190.01.14.
- "Origin of the Moon in a giant impact near the end of the Earth's formation". Nature.com. Retrieved 28 July 2009.
- "Earth life appeared on land 1.5 billion years earlier than previously thought". SpaceRef.com. Retrieved 3 July 2009.
- "The Snowball Earth". Paul F. Hoffman and Daniel P. Schrag. Harvard University. 8 August 1999. Archived from the original on 10 September 2009. Retrieved 28 July 2009.
- Morgan J.W. & Anders E. 1980. Chemical composition of Earth, Venus, and Mercury. Proceedings of the National Academy of Science 77 (12): 6973–6977. Chemical composition of Earth, Venus, and Mercury Full free text
- Chisholm, Hugh (editor). 1911. "Petrology" in the Encyclopædia Britannica, 11th edition. Cambridge University Press.
- Measuring the Earth is part of geodesy
- Senne, Joseph H. (May 2000). "Did Edmund Hillary climb the wrong mountain?". May 2000 Volume 20 Number 5. Professional Surveyor Magazine. Retrieved 24 October 2008. Italic or bold markup not allowed in:
- Sharp, David (2005-03-05). "Chimborazo and the old kilogram". The Lancet 365 (9462): 831–832. doi:10.1016/S0140-6736(05)71021-7.
- "Tall tales about highest peaks". Australian Broadcasting Corporation. Retrieved 29 December 2008.
- "7,000 m Class Remotely Operated Vehicle KAIKO 7000". Japan Agency for Marine-Earth Science and Technology (JAMSTEC). Retrieved 7 June 2008.
- Toshiro Tanimoto. "Crustal Surface of the Earth" (PDF). American Geophysical Union. Retrieved 2 August 2009.
- D. Alfé (25 April 2002). "The ab initio simulation of the Earth's core" (PDF). The Royal Society. Retrieved 2 August 2009.
- Tackley, Paul J. (2000-06-16). "Mantle convection and plate tectonics: towards an integrated physical and chemical theory". Science 288 (5473): 2002–2007. doi:10.1126/science.288.5473.2002. PMID 10856206.
- "The Crust". Oregon State University. Retrieved 3 July 2009.
- Seyfert, Carl K.; Seyfert, Carl; Seyfert, Claus (1987). The encyclopedia of structural geology and plate tectonics. Springer. ISBN 978-0-442-28125-0.
- "Plate Tectonics: plate boundaries". platetectonics.com. Retrieved 12 June 2010.
- "Understanding plate motions". USGS. Retrieved 12 June 2010.
- Oreskes, Naomi (2003). Plate tectonics: an insider's history of the modern theory of the Earth. Westview Press. ISBN 9780813341329 Check
|isbn=value: checksum (help).
- "Chapter 8: Introduction to the Hydrosphere". Physical Geography. Retrieved 6 August 2009.
- "World water resources and their uses". UNESCO. Retrieved 6 August 2009.
- "NASA - Earth's atmosphere". NASA. Retrieved 6 August 2009.
- "What causes weather?". NASA. Retrieved 6 August 2009.
- "Fundamentals of physical geography - the greenhouse effect". Physical Geography. Retrieved 6 August 2009.
- Diamond, Jared. 1997. Guns, Germs, and Steel: the fate of human societies. New York: Norton.
|Wikimedia Commons has media related to Earth.|
|The Simple English Wiktionary has a definition for: Earth and earth.|
- "Solar Views". Calvin J. Hamilton.
- "Earth – Science questions". NASA.
- "Earth – Speed through space – about 1 million miles an hour" (PDF). NASA. ("WP discussion")