One Million Things: Planet Earth

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Beneath the lithosphere is the asthenosphere , a relatively low-viscosity layer on which the lithosphere rides. Beneath the mantle, an extremely low viscosity liquid outer core lies above a solid inner core. These plumes can produce hotspots and flood basalts. The final major mode of heat loss is through conduction through the lithosphere, the majority of which occurs under the oceans because the crust there is much thinner than that of the continents. Earth's mechanically rigid outer layer, the lithosphere, is divided into tectonic plates.

These plates are rigid segments that move relative to each other at one of three boundaries types: At convergent boundaries , two plates come together; at divergent boundaries , two plates are pulled apart; and at transform boundaries , two plates slide past one another laterally. Along these plate boundaries, earthquakes , volcanic activity , mountain-building , and oceanic trench formation can occur.

As the tectonic plates migrate, oceanic crust is subducted under the leading edges of the plates at convergent boundaries. At the same time, the upwelling of mantle material at divergent boundaries creates mid-ocean ridges. The combination of these processes recycles the oceanic crust back into the mantle. The remaining Tectonics and erosion , volcanic eruptions , flooding , weathering , glaciation , the growth of coral reefs , and meteorite impacts are among the processes that constantly reshape the Earth's surface over geological time.

The continental crust consists of lower density material such as the igneous rocks granite and andesite. Less common is basalt , a denser volcanic rock that is the primary constituent of the ocean floors. The most abundant silicate minerals on Earth's surface include quartz , feldspars , amphibole , mica , pyroxene and olivine. The pedosphere is the outermost layer of Earth's continental surface and is composed of soil and subject to soil formation processes.

The total arable land is The abundance of water on Earth's surface is a unique feature that distinguishes the "Blue Planet" from other planets in the Solar System. The mass of the oceans is approximately 1. The oceans cover an area of About Most fresh water, about The atmospheric pressure at Earth's sea level averages Earth's biosphere has significantly altered its atmosphere. Oxygenic photosynthesis evolved 2. The ozone layer blocks ultraviolet solar radiation , permitting life on land.

Water vapor, carbon dioxide, methane , nitrous oxide , and ozone are the primary greenhouse gases in the atmosphere.


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Earth's atmosphere has no definite boundary, slowly becoming thinner and fading into outer space. This lowest layer is called the troposphere.

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A Love Letter to Planet Earth

Energy from the Sun heats this layer, and the surface below, causing expansion of the air. This lower-density air then rises and is replaced by cooler, higher-density air. The result is atmospheric circulation that drives the weather and climate through redistribution of thermal energy. Water vapor generated through surface evaporation is transported by circulatory patterns in the atmosphere. When atmospheric conditions permit an uplift of warm, humid air, this water condenses and falls to the surface as precipitation.

This water cycle is a vital mechanism for supporting life on land and is a primary factor in the erosion of surface features over geological periods. Precipitation patterns vary widely, ranging from several meters of water per year to less than a millimeter. Atmospheric circulation, topographic features, and temperature differences determine the average precipitation that falls in each region. The amount of solar energy reaching Earth's surface decreases with increasing latitude. At higher latitudes, the sunlight reaches the surface at lower angles, and it must pass through thicker columns of the atmosphere.

As a result, the mean annual air temperature at sea level decreases by about 0. Ranging from the equator to the polar regions, these are the tropical or equatorial , subtropical , temperate and polar climates. The highest air temperature ever measured on Earth was Above the troposphere, the atmosphere is usually divided into the stratosphere , mesosphere , and thermosphere. Beyond these, the exosphere thins out into the magnetosphere , where the geomagnetic fields interact with the solar wind. Thermal energy causes some of the molecules at the outer edge of the atmosphere to increase their velocity to the point where they can escape from Earth's gravity.

This causes a slow but steady loss of the atmosphere into space. Because unfixed hydrogen has a low molecular mass , it can achieve escape velocity more readily, and it leaks into outer space at a greater rate than other gases. Photosynthesis provided a source of free oxygen, but the loss of reducing agents such as hydrogen is thought to have been a necessary precondition for the widespread accumulation of oxygen in the atmosphere. Instead, most of the hydrogen loss comes from the destruction of methane in the upper atmosphere.

The gravity of Earth is the acceleration that is imparted to objects due to the distribution of mass within the Earth. Near the Earth's surface, gravitational acceleration is approximately 9. Local differences in topography , geology , and deeper tectonic structure cause local and broad, regional differences in the Earth's gravitational field, known as gravity anomalies. The main part of Earth's magnetic field is generated in the core, the site of a dynamo process that converts the kinetic energy of thermally and compositionally driven convection into electrical and magnetic field energy.

The field extends outwards from the core, through the mantle, and up to Earth's surface, where it is, approximately, a dipole. The poles of the dipole are located close to Earth's geographic poles. At the equator of the magnetic field, the magnetic-field strength at the surface is 3. This causes secular variation of the main field and field reversals at irregular intervals averaging a few times every million years. The most recent reversal occurred approximately , years ago.

The extent of Earth's magnetic field in space defines the magnetosphere. Ions and electrons of the solar wind are deflected by the magnetosphere; solar wind pressure compresses the dayside of the magnetosphere, to about 10 Earth radii, and extends the nightside magnetosphere into a long tail. During magnetic storms and substorms , charged particles can be deflected from the outer magnetosphere and especially the magnetotail, directed along field lines into Earth's ionosphere, where atmospheric atoms can be excited and ionized, causing the aurora. Earth's rotation period relative to the Sun—its mean solar day—is 86, seconds of mean solar time 86, For bodies near the celestial equator , this is equivalent to an apparent diameter of the Sun or the Moon every two minutes; from Earth's surface, the apparent sizes of the Sun and the Moon are approximately the same.

The orbital speed of Earth averages about The Moon and Earth orbit a common barycenter every When combined with the Earth—Moon system's common orbit around the Sun, the period of the synodic month , from new moon to new moon, is Viewed from the celestial north pole , the motion of Earth, the Moon, and their axial rotations are all counterclockwise. Viewed from a vantage point above the north poles of both the Sun and Earth, Earth orbits in a counterclockwise direction about the Sun. The orbital and axial planes are not precisely aligned: Earth's axis is tilted some Without this tilt, there would be an eclipse every two weeks, alternating between lunar eclipses and solar eclipses.

The Hill sphere , or the sphere of gravitational influence, of the Earth is about 1. Objects must orbit the Earth within this radius, or they can become unbound by the gravitational perturbation of the Sun. The axial tilt of the Earth is approximately Due to Earth's axial tilt, the amount of sunlight reaching any given point on the surface varies over the course of the year.

This causes the seasonal change in climate, with summer in the Northern Hemisphere occurring when the Tropic of Cancer is facing the Sun, and winter taking place when the Tropic of Capricorn in the Southern Hemisphere faces the Sun. During the summer, the day lasts longer, and the Sun climbs higher in the sky. In winter, the climate becomes cooler and the days shorter. In northern temperate latitudes, the Sun rises north of true east during the summer solstice, and sets north of true west, reversing in the winter. The Sun rises south of true east in the summer for the southern temperate zone and sets south of true west.

Above the Arctic Circle , an extreme case is reached where there is no daylight at all for part of the year, up to six months at the North Pole itself, a polar night. In the Southern Hemisphere, the situation is exactly reversed, with the South Pole oriented opposite the direction of the North Pole. Six months later, this pole will experience a midnight sun , a day of 24 hours, again reversing with the South Pole. By astronomical convention, the four seasons can be determined by the solstices —the points in the orbit of maximum axial tilt toward or away from the Sun—and the equinoxes , when the direction of the tilt and the direction to the Sun are perpendicular.

In the Northern Hemisphere, winter solstice currently occurs around 21 December; summer solstice is near 21 June, spring equinox is around 20 March and autumnal equinox is about 22 or 23 September.

Planet Earth: Facts About Its Orbit, Atmosphere & Size | Space

In the Southern Hemisphere, the situation is reversed, with the summer and winter solstices exchanged and the spring and autumnal equinox dates swapped. The angle of Earth's axial tilt is relatively stable over long periods of time. Its axial tilt does undergo nutation ; a slight, irregular motion with a main period of Both of these motions are caused by the varying attraction of the Sun and the Moon on Earth's equatorial bulge.

The poles also migrate a few meters across Earth's surface. This polar motion has multiple, cyclical components, which collectively are termed quasiperiodic motion. In addition to an annual component to this motion, there is a month cycle called the Chandler wobble. Earth's rotational velocity also varies in a phenomenon known as length-of-day variation. In modern times, Earth's perihelion occurs around 3 January, and its aphelion around 4 July. These dates change over time due to precession and other orbital factors, which follow cyclical patterns known as Milankovitch cycles.

The changing Earth—Sun distance causes an increase of about 6. Because the Southern Hemisphere is tilted toward the Sun at about the same time that Earth reaches the closest approach to the Sun, the Southern Hemisphere receives slightly more energy from the Sun than does the northern over the course of a year. This effect is much less significant than the total energy change due to the axial tilt, and most of the excess energy is absorbed by the higher proportion of water in the Southern Hemisphere.

A study from suggested that Planet Nine tilted all the planets of the Solar System , including Earth, by about six degrees. A planet that can sustain life is termed habitable , even if life did not originate there. Earth provides liquid water—an environment where complex organic molecules can assemble and interact, and sufficient energy to sustain metabolism. A planet's life forms inhabit ecosystems , whose total is sometimes said to form a "biosphere". Terrestrial biomes lying within the Arctic or Antarctic Circles , at high altitudes or in extremely arid areas are relatively barren of plant and animal life; species diversity reaches a peak in humid lowlands at equatorial latitudes.

In July , scientists reported identifying a set of genes from the last universal common ancestor LUCA of all organisms living on Earth. Earth has resources that have been exploited by humans. Large deposits of fossil fuels are obtained from Earth's crust, consisting of coal , petroleum , and natural gas.

Earth's biosphere produces many useful biological products for humans, including food, wood , pharmaceuticals , oxygen, and the recycling of many organic wastes. The land-based ecosystem depends upon topsoil and fresh water, and the oceanic ecosystem depends upon dissolved nutrients washed down from the land. Large areas of Earth's surface are subject to extreme weather such as tropical cyclones , hurricanes , or typhoons that dominate life in those areas.

From to , these events caused an average of 11, human deaths per year. Many localized areas are subject to human-made pollution of the air and water, acid rain and toxic substances, loss of vegetation overgrazing , deforestation , desertification , loss of wildlife, species extinction , soil degradation , soil depletion and erosion. There is a scientific consensus linking human activities to global warming due to industrial carbon dioxide emissions.

This is predicted to produce changes such as the melting of glaciers and ice sheets, more extreme temperature ranges, significant changes in weather and a global rise in average sea levels.

Our home planet provides us with life and protects us from space.

Cartography , the study and practice of map-making, and geography , the study of the lands, features, inhabitants and phenomena on Earth, have historically been the disciplines devoted to depicting Earth. Surveying , the determination of locations and distances, and to a lesser extent navigation , the determination of position and direction, have developed alongside cartography and geography, providing and suitably quantifying the requisite information.

Earth's human population reached approximately seven billion on 31 October Human population density varies widely around the world, but a majority live in Asia. The northernmost permanent settlement in the world is Alert , on Ellesmere Island in Nunavut , Canada. Independent sovereign nations claim the planet's entire land surface, except for some parts of Antarctica, a few land parcels along the Danube river's western bank, and the unclaimed area of Bir Tawil between Egypt and Sudan.

As of [update] , there are sovereign states that are member states of the United Nations , plus two observer states and 72 dependent territories and states with limited recognition. The United Nations is a worldwide intergovernmental organization that was created with the goal of intervening in the disputes between nations, thereby avoiding armed conflict. When the consensus of the membership permits, it provides a mechanism for armed intervention. The first human to orbit Earth was Yuri Gagarin on 12 April The station's crew , made up of six people, is usually replaced every six months.

Earth's formation and evolution

The Moon is a relatively large, terrestrial , planet-like natural satellite , with a diameter about one-quarter of Earth's. It is the largest moon in the Solar System relative to the size of its planet, although Charon is larger relative to the dwarf planet Pluto. The natural satellites of other planets are also referred to as "moons", after Earth's. The gravitational attraction between Earth and the Moon causes tides on Earth. The same effect on the Moon has led to its tidal locking : its rotation period is the same as the time it takes to orbit Earth.

As a result, it always presents the same face to the planet. As the Moon orbits Earth, different parts of its face are illuminated by the Sun, leading to the lunar phases ; the dark part of the face is separated from the light part by the solar terminator. The Moon may have dramatically affected the development of life by moderating the planet's climate.

Paleontological evidence and computer simulations show that Earth's axial tilt is stabilized by tidal interactions with the Moon. Viewed from Earth, the Moon is just far enough away to have almost the same apparent-sized disk as the Sun. The angular size or solid angle of these two bodies match because, although the Sun's diameter is about times as large as the Moon's, it is also times more distant.

The most widely accepted theory of the Moon's origin, the giant-impact hypothesis , states that it formed from the collision of a Mars-size protoplanet called Theia with the early Earth. This hypothesis explains among other things the Moon's relative lack of iron and volatile elements and the fact that its composition is nearly identical to that of Earth's crust.

Earth has at least five co-orbital asteroids , including Cruithne and AA The tiny near-Earth asteroid RH makes close approaches to the Earth—Moon system roughly every twenty years. During these approaches, it can orbit Earth for brief periods of time. The standard astronomical symbol of Earth consists of a cross circumscribed by a circle , , [] representing the four corners of the world.

Human cultures have developed many views of the planet. In many cultures it is a mother goddess that is also the primary fertility deity , [] and by the midth century, the Gaia Principle compared Earth's environments and life as a single self-regulating organism leading to broad stabilization of the conditions of habitability. Scientific investigation has resulted in several culturally transformative shifts in people's view of the planet. Initial belief in a flat Earth was gradually displaced in the Greek colonies of southern Italy during the late 6th century BC by the idea of spherical Earth , [] [] [] which was attributed to both the philosophers Pythagoras and Parmenides.

It was only during the 19th century that geologists realized Earth's age was at least many millions of years. From Wikipedia, the free encyclopedia. This article is about the planet. For its human aspects, see World. For other uses, see Earth disambiguation and Planet Earth disambiguation. Third planet from the Sun in the Solar System. The Blue Marble , the first full-view photograph of the planet, was taken by Apollo 17 astronauts en route to the Moon in Semi-major axis.

Orbital period. Average orbital speed. Mean anomaly. Equatorial radius. Polar radius. Surface area. Mean density. Surface gravity. Moment of inertia factor. Escape velocity.

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Sidereal rotation period. Axial tilt. Surface pressure. Main article: History of Earth. Main article: Geological history of Earth. Life timeline. This box: view talk edit. Single-celled life. Multicellular life. Earliest water.


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  8. Earliest life. Earliest oxygen. Atmospheric oxygen. Oxygen crisis. Sexual reproduction. Earliest plants. Ediacara biota. Cambrian explosion. Earliest apes. See also: Human timeline , and Nature timeline.

    DK Science: Planet Earth

    Main articles: Abiogenesis and Evolutionary history of life. Main article: Future of Earth. See also: Global catastrophic risk. Main articles: Figure of the Earth , Earth radius , and Earth's circumference. See also: Abundance of elements on Earth. Main article: Structure of the Earth. Main article: Earth's internal heat budget. Pacific Plate. African Plate [n 16]. North American Plate. Eurasian Plate. Antarctic Plate. Indo-Australian Plate. South American Plate. Main article: Plate tectonics. Main article: Hydrosphere. Main article: Atmosphere of Earth. Main articles: Weather and Climate.

    Hurricane Felix seen from low Earth orbit, September Lenticular cloud over an ice pressure ridge near Mount Discovery , Antarctica , November Massive clouds above the Mojave Desert , February Main article: Gravity of Earth. Main article: Earth's magnetic field. Main article: Magnetosphere. Main article: Earth's rotation. Main article: Earth's orbit. Main article: Biosphere.

    Main articles: Natural resource and Land use. Main articles: Human geography and World. Main article: Moon. Main article: Earth in culture. Gould Belt. Orion Arm. Virgo SCl. Laniakea SCl. Celestial sphere Earth phase Earth physical characteristics tables Earth science Earth system science List of gravitationally rounded objects of the Solar System Outline of Earth Timeline of natural history Timeline of the far future.

    The quantities given are the values at the instant J The difference between Earth's perihelion and aphelion is 5 million kilometers. February Orbital Debris Quarterly News. Retrieved 18 April Based on data from the Vector Map and Global Landcover Archived 26 March at the Wayback Machine datasets, extreme values for coverage of lakes and streams are 0. The ice shields of Antarctica and Greenland are counted as land, even though much of the rock that supports them lies below sea level. Over a year, this discrepancy adds up to a full sidereal day.

    Paula Danziger. The Most Important Thing. Matthew Landis. Georgia Bragg. Max Brallier and Douglas Holgate. The Beloved World of Sonia Sotomayor. Sonia Sotomayor. Saving Fable. Scott Reintgen. The Collected Works of Gretchen Oyster. Ted Anderson and Katie Cook.

    Katy Keene. Archie Superstars. Disney Storied Places. Rhona Cleary , Eduardo Jauregui and Various. Paper World: Planet Earth. Unusual Chickens for the Exceptional Poultry Farmer. Judy Goldman. Timmy Failure: Sanitized for Your Protection. Stephan Pastis. The Law of Finders Keepers. Sheila Turnage. Women in Art. Rachel Ignotofsky. The Creakers. Scientists refer to this turning point as the Mid-Pleistocene Transition , and the new pattern has persisted right through the last ice age, which ended about 15, years ago.

    However, the exact reason as to why this pattern has remained is a scientific enigma. Subscribe to our mailing list and get the latest content delievered to your email! Don't worry, we never send spam!. Enter your Email address.

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