Land

The Earth (from the Latin Terra, Roman deity equivalent to Gaia, Greek goddess of femininity and fertility) is a planet in the solar system that revolves around its star — the Sun—in the third innermost orbit. It is the densest and fifth largest of the eight planets in the solar system. It is also the largest of the four terrestrial or rocky.

Earth formed approximately 4.55 billion years ago and life arose some billion years later. It is home to millions of species, including humans, and is currently the only astronomical body where life is known to exist. The atmosphere and other abiotic conditions have been significantly altered by the planet's biosphere, favoring the proliferation of aerobic organisms, as well as the formation of an ozone layer that, together with the Earth's magnetic field, blocks harmful solar radiation, thus allowing the life on Earth. The physical properties of Earth, geological history, and its orbit have allowed life to continue to exist. It is estimated that the planet will continue to be capable of supporting life for another 500 million years, since according to current forecasts, after that time the increasing luminosity of the Sun will end up causing the extinction of the biosphere.

The earth's surface or crust is divided into several tectonic plates that slide on magma over periods of several million years. The surface is covered by continents and islands; These have several lakes, rivers and other sources of water, which together with the saltwater oceans that represent about 71% of the surface constitute the hydrosphere. No other planet is known to have this balance of liquid water, which is essential for any known life. The Earth's poles are mostly covered with solid ice (Antarctica ice cap) or ice sheets (Arctic ice cap). The interior of the planet is geologically active, with a thick layer of relatively solid mantle, a liquid outer core that generates a magnetic field, and a solid inner core made up of approximately 88% iron.

Earth interacts gravitationally with other objects in space, especially the Sun and the Moon. Currently, the Earth completes one orbit around the Sun every time it makes 366.26 turns on its axis, which is equivalent to 365.26 solar days or one sidereal year. The Earth's axis of rotation is tilted 23.4° with respect to the perpendicular to its orbital plane, which produces seasonal variations on the planet's surface with a period of one tropical year (365.24 solar days). The Earth has a single natural satellite, the Moon, which began to orbit the Earth 4.53 billion years ago; This produces the tides, stabilizes the inclination of the Earth's axis and gradually reduces the speed of the planet's rotation. Approximately 3.8 to 4.1 billion years ago, during the so-called late heavy bombardment, numerous asteroids impacted the Earth, causing significant changes to most of its surface.

Both the planet's minerals and the products of the biosphere contribute resources that are used to sustain the world's human population. Its people are grouped into some 200 independent sovereign states, which interact through diplomacy, travel, trade, and military action. Human cultures have developed many ideas about the planet, including the personification of a deity, a belief in a flat Earth or the Earth as the center of the universe, and a modern perspective of the world as an integrated environment that requires management.

Timeline

Scientists have been able to piece together detailed information about Earth's past. According to these studies, the oldest material in the solar system formed 4567.2 ± 0.6 million years ago, and around 4550 million years ago. Earth and the other planets of the solar system had already formed before (with an uncertainty of 1%) from the solar nebula, a disk-shaped mass composed of dust and gas left over from the formation of the Sun. This process The formation of Earth through accretion took place mostly within 10–20 million years. The planet's outer shell, initially molten, cooled to a solid crust as water began to accumulate in the atmosphere. The Moon formed shortly before, about 4.53 billion years ago.

Graphic representation of the theory of great impact.

The current consensus model for the formation of the Moon is the big impact theory, which postulates that the Moon was created when an object the size of Mars, with about 10% of the mass of Earth, impacted tangentially against it. In this model, part of the mass of this body could have merged with the Earth, while another part would have been ejected into space, providing enough material in orbit to trigger again a process of clumping by gravitational forces, and thus forming the Moon.

Outgassing of the crust and volcanic activity produced Earth's primordial atmosphere. Condensation of water vapor, together with ice and liquid water contributed by asteroids and by protoplanets, comets, and trans-Neptunian objects, produced the oceans. The newly formed Sun was only 70% as luminous as it is today: however, there is evidence that shows that the primitive oceans remained in a liquid state; a contradiction called the "weak young sun paradox", since apparently water should not be able to remain in that liquid state, but in the solid, due to little solar energy received. However, a combination of gases The greenhouse effect and increased levels of solar activity contributed to raising the temperature of the Earth's surface, thus preventing the oceans from freezing. 3.5 billion years ago the Earth's magnetic field formed, helping to prevent the atmosphere from being blown by the solar wind.

Two models have been proposed for the growth of the continents: the constant growth model, and the rapid growth model early in Earth's history. Current research suggests that the second option is most likely, with initial rapid growth of the continental crust, followed by a long period of stability. On time scales of hundreds of millions of years, the Earth's surface has been constantly reshaping, forming and fragmenting continents. These continents have drifted across the surface, sometimes combining to form a supercontinent. Approximately 750 million years (ma) ago, one of the earliest known supercontinents, Rodinia, began to crack apart. The continents later recombined to form Pannotia, between 600 to 540 Ma, and finally Pangea, which broke up 180 Ma ago to its present continental configuration.

Evolution of Life

Earth provides the only known example of an environment that has given rise to the evolution of life. Highly energetic chemical processes are presumed to have produced a self-replicating molecule around 4 billion years ago, and between 3.5 billion years ago. and 3.8 billion years ago the last universal common ancestor existed. The development of photosynthesis allowed living beings to directly collect energy from the Sun; the resulting oxygen accumulated in the atmosphere formed ozone (a form of molecular oxygen [O₃]) in the upper atmosphere. The incorporation of smaller cells into larger ones resulted in the development of complex cells called eukaryotes. True multicellular organisms formed when cells within colonies became increasingly specialized. Life colonized the Earth's surface in part through the absorption of ultraviolet radiation by the ozone layer.

In the 1960s a hypothesis emerged that during the Neoproterozoic period, from 750 to 580 Ma, there was an intense glaciation in which much of the planet was covered by an ice sheet. This hypothesis has been termed the "global glaciation", and is of particular interest, as this event preceded the so-called Cambrian explosion, in which multicellular life forms began to proliferate.

Following the Cambrian explosion, about 535 Ma, there have been five mass extinctions. Of these, the most recent event occurred 65 Ma, when an asteroid impact caused the extinction of non-avian dinosaurs, as well as as well as other large reptiles, surviving some small animals such as mammals, which at that time were similar to the current shrews. Over the past 65 million years mammals diversified, until several million years ago an ape-like African animal known as the orrorin tugenensis gained the ability to stand on its feet. This enabled it to use tools and enhanced its ability to stand. of communication, providing the necessary nutrition and stimulation to develop a larger brain, and thus allowing the evolution of the human species. The development of agriculture and civilization allowed humans to alter the Earth in a short space of time as no other species had done, affecting both nature and the diversity and quantity of life forms.

The present pattern of ice ages began around 40 Ma and then intensified during the Pleistocene around 3 Ma. Since then, high-latitude regions have been subject to repeated cycles of glaciation and melting, in cycles from 40-100 thousand years. The last continental ice age ended 10,000 years ago.

Future

Cycle of solar life.

The future of the planet is closely tied to that of the Sun. As a result of the constant accumulation of helium in the Sun's core, the total luminosity of the star will gradually increase. The Sun's luminosity will grow by 10% in the next 1.1 Ga (1.1 billion years) and by 40% in the next 3.5 Ga. Climate models indicate that increased radiation could have dire consequences on Earth, including the loss of the planet's oceans.

Earth is expected to be habitable for about another 500 million years from now, though this period could be extended to 2.3 billion years if nitrogen is removed from the atmosphere. the earth's surface will accelerate the cycle of inorganic CO2, reducing its concentration to lethally low levels for plants (10 ppm for C4 photosynthesis) within approximately 500 to 900 million years. The lack of vegetation will result in the loss of oxygen in the atmosphere, causing the extinction of animal life over several million more years. After another billion years, all surface water will have disappeared and the global mean temperature will reach 70 °C. Even if the Sun were eternal and stable, the continued cooling of the Earth's interior would result in a large loss of CO₂ due to reduced activity volcanic, and 35% of the water in the oceans could sink into the mantle due to decreased venting steam at mid-ocean ridges.

The Sun, following its natural evolution, will become a red giant in about 5 Ga. Models predict that the Sun will expand to about 250 times its current size, reaching a radius of about 1 AU (about 150 million km). The fate of Earth then is unclear. Being a red giant, the Sun will lose about 30% of its mass, so without tidal effects, Earth will move into an orbit of 1.7 AU (about 250 million kilometers) from the Sun when the star reach its maximum radius. The planet is therefore expected to initially escape being engulfed by the Sun's tenuous expanded outer atmosphere. Even so, any remaining life would be destroyed by the Sun's increased luminosity (peaking at about 5,000 times its current level). However, a 2008 simulation indicates that Earth's orbit will decay due to tidal and drag effects, causing the planet to enter the stellar atmosphere and vaporize.

Composition and structure

Earth is a terrestrial planet, which means it is a rocky body and not a gas giant like Jupiter. It is the largest of the four terrestrial planets in the solar system in size and mass, and is also the one with the highest density, greatest surface gravity, strongest magnetic field, and fastest rotation of the four. The only terrestrial planet with active tectonic plates. The movement of these plates causes the Earth's surface to be in constant change, being responsible for the formation of mountains, seismicity and volcanism. The cycle of these plates also plays a preponderant role in the regulation of the Earth's temperature, contributing to the recycling of greenhouse gases such as carbon dioxide, through the permanent renewal of the ocean floors.

Shape

Comparison of size of the inner planets (from left to right): Mercury, Venus, Earth and Mars.

The shape of the Earth is very similar to that of an oblate spheroid, a sphere flattened at the poles, resulting in a bulge around the equator. This bulge is caused by the rotation of the Earth, and causes the diameter at the equator is 43 km longer than the diameter from pole to pole. About 22,000 years ago the Earth was more spherical in shape, most of the northern hemisphere was covered by ice, and as the ice melted it caused less pressure on the Earth's surface on which it rested, causing a type of "rebound". This phenomenon continued to occur until the mid-1990s, when scientists realized that this process had been reversed, i.e., the bulge was increasing. Observations from the GRACE satellite show that, at least since 2002, ice loss from Greenland and Antarctica has been primarily responsible for this trend.

Chimborazo Volcano, the Earth's most distant point in the center of the Earth.

The local topography deviates from this idealized spheroid, although the differences on a global scale are very small: Earth is offset by about one part in 584, or 0.17%, from the reference spheroid, which is less than the 0.22% tolerance allowed for billiard balls. The largest local deviations in the rocky surface of the Earth are Mount Everest (8,848 m above local sea level) and Challenger Deep, to the south from the Mariana Trench (10,911 m below local sea level). Due to the equatorial bulge, the furthest land point from the center of the Earth is the Chimborazo volcano in Ecuador.

Size

The circumference at the equator is 40 091 km. The diameter at the equator is 12,756 km and at the poles 12,730 km.

The mean reference diameter for the spheroid is about 12 742 km, which is about 40 000 km/π, as the meter was originally defined as one ten-millionth of the distance from the equator to the North Pole via Paris, France.

The first measurement of the size of the Earth was made by Eratosthenes, in 240 BC. C.. At that time it was accepted that the Earth was spherical. Eratosthenes calculated the size of the Earth by measuring the angle at which the Sun shone at the solstice, both at Alexandria and at Siena, 750 km away. The size he got was a diameter of 12,000 km and a circumference of 40,000 km, that is, with an error of only 6% compared to the current data.

Posidonius of Apamea later repeated the measurements in the year 100 BC. C., obtaining the data of 29 000 km for the circumference, considerably more imprecise with respect to the current data. This last value was the one accepted by Ptolemy, so that value prevailed in the following centuries.

When Magellan circled the entire planet in 1521, the figure calculated by Eratosthenes was restored.

Chemical composition

The mass of the Earth is approximately 5.98×10²⁴ kg. It consists mainly of iron (32.1%), oxygen (30.1%), silicon (15.1%), magnesium (13.9%), sulfur (2.9%), nickel (1.8%)), calcium (1.5%), and aluminum (1.4%), with the remaining 1.2% made up of trace amounts of other elements. Due to mass segregation, the core zone is believed to be composed primarily of iron (88.8%), with small amounts of nickel (5.8%), sulfur (4.5%), and less than 1 % formed by traces of other elements.

Geochemist F. W. Clarke (1847-1931), called "the father of geochemistry for having determined the composition of the Earth's crust," calculated that just over 47% of the Earth's crust is made up of oxygen. The most common rock components of the Earth's crust are almost all oxides. Chlorine, sulfur, and fluorine are the only significant exceptions, and their total presence in any rock is generally much less than 1%. The main oxides are silica, alumina, iron oxide, calcium, magnesium, potassium and sodium. Silica acts mainly as an acid, forming silicates, and the most common minerals in igneous rocks are of this nature. From a calculation based on 1,672 analyzes of all types of rocks, Clarke deduced that 99.22% of rocks are made up of 11 oxides (see chart to the right). All other compounds appear only in very small amounts.

Internal structure

The interior of Earth, like that of the other terrestrial planets, is divided into layers based on its chemical composition or its physical (rheological) properties, but unlike the other terrestrial planets, it has an inner core and different external Its outer layer is a chemically differentiated solid silicate crust, under which is a highly viscous solid mantle. The crust is separated from the mantle by the Mohorovičić discontinuity, its thickness varying from an average of 6 km in the oceans to between 30 and 50 km in the continents. The crust and the cold, rigid top of the upper mantle are commonly known as the lithosphere, and it is the lithosphere that tectonic plates are made of. Beneath the lithosphere is the asthenosphere, a layer of relatively low viscosity on which the lithosphere floats. Within the mantle, between 410 and 660 km below the surface, important changes in the crystalline structure occur. These changes create a transition zone that separates the upper and lower parts of the mantle. Beneath the mantle is an extremely low-viscosity liquid outer core, resting on a solid inner core. The inner core can rotate with a slightly higher angular velocity than the rest of the planet, advancing 0.1 to 0.5° per second. year.

Geological Capas of the Earth

Cutting the Earth from the core to the exosphere (not on a scale).	Deep km	Capture components	Density g/cm3
	0-60	Litosfera	-
	0-35	Cortez	2.2-2.9
	35-60	Upper mantle	3.4-4.4
	35-2890	Manto	3.4-5.6
	100-700	Astenosfer	-
	2890-5100	External core	9,9-12,2
	5100-6378	Inner core	12.8-13.1

Heat

Earth's internal heat comes from a combination of residual heat from planetary accretion (20%) and heat produced by radioactive decay (80%). The most heat-producing isotopes on Earth are potassium-40, uranium-238, uranium-235, and thorium-232. At the center of the planet, the temperature can be as high as 7,000 K and the pressure can be as high as 360 GPa. Because much of the As heat is provided by radioactive decay, scientists believe that in Earth's early history, before the short-lived isotopes ran out, Earth's heat production was much greater. This extra heat production, which approximately 3 billion years ago was twice current production, may have increased temperature gradients within the Earth, increasing mantle convection and plate tectonics, allowing for the production of rocks. igneous such as komatites that do not form today.

The average heat loss from Earth is 87 mW m⁻², which is an overall loss of 4.42 × 10¹³ W. Some of the thermal energy from the core is transported to the crust by mantle plumes, some form of convection consisting of rock outcroppings at high temperatures. These plumes can produce hot spots and basalt flows. Most of the heat lost from Earth seeps between tectonic plates, in mantle upwelling associated with mid-ocean ridges. Most of the remaining losses occur by conduction through the lithosphere, mainly in the oceans, since the crust there is much thinner than on the continents.

Plate tectonics

Tectonic plates

Name of the plate	Area 106km2
African Plate	78.0
Antarctica	60.9
Indoaustralian Plate	47.2
Eurasian Plate	67.8
North American Plate	75.9
South American Plate	43.6
Pacific Plate	103.3

Earth's mechanically rigid outer layer, the lithosphere, is broken into pieces called tectonic plates. These plates are rigid elements that move relative to one another in one of three patterns: converging edges, where two plates approach each other; divergent boundaries, where two plates move apart; and transform boundaries, where two plates slide past each other. Along these plate boundaries, earthquakes, volcanic activity, mountain building, and the formation of ocean trenches occur. Plate tectonics slide on top of the asthenosphere, the solid but less viscous upper section of the planet. mantle, which can flow and move along with the plates, and whose movement is strongly associated with convection patterns within the Earth's mantle.

As tectonic plates migrate across the planet, the ocean floor is subducted under the plate boundaries at convergent boundaries. At the same time, upwelling of mantle material at divergent boundaries creates mid-ocean ridges. The combination of these processes continually recycles the oceanic crust back into the mantle. Due to this recycling process, most of the ocean floor is less than 100 million years old. The oldest oceanic crust is found in the Western Pacific, and is estimated to be about 200 million years old. By comparison, the oldest recorded continental crust is 4.03 billion years old.

The seven largest plates are the Pacific, North American, Eurasian, African-Antarctic, Indo-Australian, and South American plates. Other notable plates are the Indian Plate, the Arabian Plate, the Caribbean Plate, the Nazca Plate on the western coast of South America, and the Scottish Plate in the southern Atlantic Ocean. The Australian Plate merged with the Indian Plate between 50 and 55 million years ago. The fastest moving plates are the oceanic plates, with the Cocos plate advancing at a rate of 75 mm/yr and the Pacific plate moving 52-69 mm/yr. At the other extreme, the slowest moving plate is the Eurasian plate, which moves at a typical rate of about 21 mm/yr.

Surface

Histogram of elevation of the earth's crust.

Earth's relief varies greatly from place to place. About 70.8% of the surface is covered by water, with much of the continental shelf below sea level. The submerged surface has montaneous features, including a system of mid-ocean ridges, as well as submarine volcanoes, mid-ocean trenches, submarine canyons, plateaus, and abyssal plains. The remaining 29.2% not covered by water is made up of mountains, deserts, plains, plateaus, and other geomorphologies.

The surface of the planet is shaped over geologic periods of time, due to tectonic erosion. Features on this surface formed or deformed by plate tectonics are subject to constant erosion from precipitation, thermal cycling, and chemical effects. Glaciation, coastal erosion, the buildup of coral reefs, and major meteorite impacts also act to reshape the landscape.

Altimetry and current blending. Data from the Digital Land Model of the National Geophysical Data Center of the United States.

The continental crust is made up of lower-density material, such as igneous rocks, granite, and andesite. Less common is basalt, a dense volcanic rock that is the main component of the ocean floor. Sedimentary rocks are formed by the accumulation of compacted sediments. Almost 75% of the continental surface is covered by sedimentary rocks, despite the fact that these only form 5% of the crust. The third most abundant rock material on Earth is metamorphic rocks, created from the transformation of existing rock types by high pressure, high temperature, or both. The most abundant silicate minerals on Earth's surface include quartz, feldspars, amphibole, mica, pyroxene, and olivine. The most common carbonate minerals are calcite (found in limestone) and the dolomite.

The pedosphere is the outermost layer of Earth. It is composed of earth and is subject to soil formation processes. It exists at the meeting point between the lithosphere, the atmosphere, the hydrosphere and the biosphere. Currently, 13.31% of the total land surface is arable land, and only 4.71% supports permanent crops. About 40% of the emerged surface is currently used as cropland and pasture, estimating a total of 1.3×10⁷ km² for cropland and 3.4×10⁷ km² for grazing land.

The elevation of the land surface ranges from a low point of −418 m at the Dead Sea to a maximum elevation, estimated in 2005, of 8,848 m at the top of Mount Everest. The average height of the earth above sea level is 840 m.

Satellite images of the Earth

Ground floor plan (composition of satellite photos).

ESA's Envisat environmental satellite has developed a detailed portrait of the Earth's surface. Through the GLOBCOVER project, the creation of a global map of land cover was developed with a resolution three times higher than that of any other satellite map up to that time. He used radar reflectors with synthetic wide antennas, capturing the reflected radiation with his sensors.

NASA has completed a new three-dimensional map, which is the most accurate topography of the planet, produced over four years with data transmitted by the space shuttle Endeavour. The data analyzed corresponds to 80% of the terrestrial mass. Covers the territories of Australia and New Zealand in unprecedented detail. It also includes more than a thousand Polynesian and Melanesian islands in the South Pacific, as well as islands in the Indian Ocean and the Atlantic. Many of these islands barely rise a few meters above sea level and are very vulnerable to the effects of tidal waves and storms, so knowing them will help prevent catastrophes; the data provided by the Endeavor mission will have a wide variety of uses, such as virtual exploration of the planet.

Hydrosphere

The oceans possess the largest volume of water on Earth.

The abundance of water on Earth's surface is a unique feature that distinguishes the "Blue Planet" from others in the Solar System. Earth's hydrosphere is composed primarily of oceans, but technically includes all water surfaces in the world, including inland seas, lakes, rivers, and groundwater to a depth of 2,000 m. The deepest place under water is the Challenger Deep of the Mariana Trench in the Pacific Ocean, with a depth of −10,911.4 m.

The mass of the oceans is about 1.35×10¹⁸ metric tons, or about 1/4400 of the total mass of the Earth. The oceans cover an area of 361.84×10⁶ km² with an average depth of 3682.2 m, resulting in an estimated volume of 1.3324×10⁹ km³. If the entire earth's surface were leveled, water would cover the planet's surface to a height of more than 2.7 km. The total area of the Earth is 5.1×10⁸ km². To the first approximation, the average depth would be the ratio of the two, or 2.7 km. Approximately 97.5% of the water is salty, while the remaining 2.5% is freshwater. Most of the fresh water, approximately 68.7%, is currently in the state of ice.

The average salinity of the oceans is about 35 grams of salt per kilogram of water (35 ‰). Most of this salt was released by volcanic activity, or extracted from already cooled igneous rocks. The oceans are also a reservoir of dissolved atmospheric gases, which are essential for the survival of many forms of aquatic life. Ocean water has an important influence on the planet's climate, acting as a large heat source. Changes in the ocean temperature distribution can cause climatic disturbances, such as the Southern Oscillation, El Niño.

Atmosphere

Mean atmospheric pressure at sea level is around 101.325 kPa, with a height scale of approximately 8.5 km. It is composed primarily of 78% nitrogen and 21% oxygen, with traces of water vapor, carbon dioxide and other gaseous molecules. The height of the troposphere varies with latitude, between 8 km at the poles and 17 km at the equator, with some variation due to weather and seasonal factors.

Earth's biosphere has significantly altered the atmosphere. Oxygenic photosynthesis evolved 2.7 billion years ago, primarily forming today's nitrogen-oxygen atmosphere. This change allowed the proliferation of aerobic organisms, as well as the formation of the ozone layer that blocks ultraviolet radiation from the Sun, allowing life outside of water. Other important functions of the atmosphere for life on Earth include transporting water vapor, providing useful gases, burning up small meteorites before they reach the surface, and moderating temperatures. This latter phenomenon is known as the greenhouse effect.: traces of molecules present in the atmosphere capture the thermal energy emitted from the ground, thus increasing the average temperature. Carbon dioxide, water vapor, methane, and ozone are the major greenhouse gases in Earth's atmosphere. Without this heat retention effect, the average surface temperature would be −18 °C and life would probably not exist.

Climate and Weather

Satellite image of Earth's nubosity using NASA's mid-resolution imaging spectrometer.

Earth's atmosphere has no sharp boundaries, gradually thinning until it vanishes into outer space. Three quarters of the atmospheric mass is contained within the first 11 km of the planet's surface. This lower layer is called the troposphere. The Sun's energy heats this layer and the surface below it, causing the air to expand. The hot air rises due to its lower density, being replaced by air of higher density, that is, colder air. This results in atmospheric circulation that generates weather and climate through the redistribution of thermal energy.

The main lines of atmospheric circulation are the trade winds in the equatorial region below 30° latitude, and the westerlies in mid-latitudes between 30° and 60°. Ocean currents are also factors important in determining climate, especially the thermohaline circulation that distributes thermal energy from the equatorial oceans to the polar regions.

Water vapor generated through surface evaporation is transported according to the circulation patterns of the atmosphere. When atmospheric conditions allow warm, moist air to rise, water condenses and settles on the surface as precipitation. Most of the water is transported to lower altitudes by river systems and usually returns to oceans or is deposited in lakes. This water cycle is a vital mechanism for supporting life on earth and is a primary factor in the erosion that shapes the earth's surface over geological periods. Precipitation patterns vary enormously, from several meters of water per year to less than a millimeter. Atmospheric circulation, topological features, and temperature differences determine the average rainfall for each region.

The amount of solar energy reaching Earth decreases with increasing latitude. At higher latitudes, sunlight hits the surface at a smaller angle, having to pass through thick columns of atmosphere. As a result, the mean annual air temperature at sea level decreases by approximately 0.4 °C for every degree of latitude moving away from the equator. The Earth can be subdivided into more or less homogeneous latitudinal strips with specific climates. From the equator to the polar regions, there are the intertropical (or equatorial) zone, the subtropical climate, the temperate climate, and the polar climates. Climate can also be classified based on temperature and rainfall, into climate regions characterized by fairly uniform air masses. The most widely used classification methodology is the Köppen climate classification (modified by Wladimir Peter Köppen's student, Rudolph Geiger), which has five large groups (humid tropical zones, arid zones, mid-latitude humid zones, continental climate, and cold polar), which are divided into more specific subtypes.

Upper atmosphere

From this point of view the Moon is partially darkened and deformed by the Earth's atmosphere. Image of NASA.

Above the troposphere, the atmosphere is usually divided into the stratosphere, mesosphere, and thermosphere. Each layer has a different adiabatic gradient, which defines the rate of change of temperature with respect to height. Beyond these is the exosphere, which fades into the magnetosphere, where Earth's magnetic fields interact with the solar wind. Within the stratosphere is the ozone layer; a component that partially protects the earth's surface from ultraviolet light, being an important element for life on Earth. The Kármán line, defined at 100 km above the Earth's surface, is a practical definition used to establish the boundary between the atmosphere and space.

Thermal energy causes some of the molecules at the outer edge of Earth's atmosphere to speed up enough to escape the planet's gravity. This results in a slow but steady loss of the atmosphere into space. Because unfixed hydrogen has a low molecular weight, it can reach escape velocity more easily, thus escaping into outer space at a higher rate than other gases. The loss of hydrogen to space contributes to Earth's transformation from its initial reducing state to its current oxidizing state. 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. Thus, the ability of hydrogen to escape from the atmosphere of Earth may have influenced the nature of life on the planet. In today's oxygen-rich atmosphere, most hydrogen is converted to water before it has a chance to escape. Instead, most of today's hydrogen loss comes from the destruction of methane in the upper atmosphere.

Magnetic field

Earth magnetosphere scheme. Solar wind flows, from left to right

Earth's magnetic field is similar in shape to a magnetic dipole, with the poles currently located near the planet's geographic poles. At the equator of the magnetic field (magnetic equator), the magnetic field strength at the surface is 3.05 × 10⁻⁵T, with a global dipole magnetic moment of 7.91 × 10¹⁵ T m³. According to dynamo theory, the field It is generated in the molten outer core, a region where heat creates convection movements in conductive materials, generating electrical currents. These currents in turn induce the Earth's magnetic field. Convective motions in the core are chaotic; the magnetic poles move and periodically change orientation. This results in geomagnetic reversals at irregular time intervals, a few times every million years. The most recent reversal took place approximately 700,000 years ago.

The magnetic field forms the magnetosphere, which deflects particles from the solar wind. In the direction of the Sun, the arc shock between the solar wind and the magnetosphere is about 13 times the radius of the Earth. The collision between the magnetic field and the solar wind forms the Van Allen radiation belts; a pair of concentric, toric-shaped regions made up of highly energetic charged particles. When plasma enters the Earth's atmosphere through the magnetic poles, polar auroras are created.

Rotation and orbit

Rotation

Inclination of the Earth axis (or obliqueness) and its relation to the rotation axis and orbital plane.

The period of rotation of the Earth with respect to the Sun, that is, a solar day, is about 86,400 seconds of solar time (86,400.0025 SIU seconds). Earth's solar day is now slightly longer than it was during the 19th century due to tidal acceleration, days are between 0 and 2 ms SIU plus.

The rotation of the Earth photographed by DSCOVR EPIC on May 29, 2016, a few weeks before the solstice.

The period of Earth's rotation relative to the fixed stars, called a stellar day by the International Earth Rotation and Reference Systems Service (IERS), is 86 164.098903691 seconds mean solar time (UT1), or 23^h 56 ^m 4.098903691^s. The period of Earth's rotation in relation to the vernal equinox, misnamed the sidereal day, is 86 164.09053083288 seconds mean solar time (UT1) (23^h 56^m 4.09053083288_s)). Therefore, the sidereal day is shorter than the stellar day by about 8.4 ms. The length of the mean solar day in SIU seconds is available from the IERS for the periods 1623-2005 and 1962-2005.

Apart from meteors in the atmosphere and satellites in low orbit, the apparent movement of celestial bodies as seen from Earth is westward at a speed of 15°/h = 15′/min. For masses near the celestial equator, this is equivalent to one apparent diameter of the Sun or Moon every two minutes (from the planet's surface, the apparent sizes of the Sun and Moon are approximately equal).

Orbit

Illustration of the Milky Way galaxy, showing the position of the Sun

Earth orbits the Sun at an average distance of about 150 million kilometers, completing one orbit every 365.2564 solar days, or one sidereal year. From Earth, this results in an apparent eastward motion of the Sun, moving relative to the stars at a rate of about 1°/day, or one diameter of the Sun or Moon every 12 hours. Due to this movement, on average the Earth takes 24 hours (one solar day) to complete one rotation on its axis until the sun returns to the meridian. Earth's orbital speed is about 29.8 km/s (107,000 km/h), which is fast enough to travel the diameter of the planet (12,742 km) in seven minutes, or the distance between Earth and the Moon (384,000 km) in four hours.

The Moon revolves with the Earth around a common barycenter, because it is inside the Earth, 4541 km from its center, the Earth-Moon system is not a double planet, the Moon completes one rotation every 27.32 days relative to the background stars. When combined with the common revolution of the Earth-Moon system around the Sun, the period of the synodic month, from one new moon to the next, is 29.53 days. Viewed from the north celestial pole, the motion of the Earth, the Moon, and their axial rotations are all counterclockwise. Viewed from a point of view located over the north poles of the Sun and Earth, the Earth would appear to revolve counterclockwise around the Sun. The orbital and axial planes are not aligned: The Earth's axis is tilted about 23.4 degrees from the perpendicular to the Earth-Sun plane, and the plane between the Earth and the Moon is tilted about 5 degrees from the Earth-Sun plane. Without this tilt, there would be an eclipse every two weeks, alternating between lunar eclipses and solar eclipses.

The Hill sphere, or gravitational sphere of influence, of Earth is about 1.5 Gm (or 1,500,000 kilometers) in radius. This is the maximum distance over which Earth's gravitational influence it is stronger than that of the more distant Sun and other planets. Objects must orbit Earth within this radius, or they will end up caught in the Sun's gravitational disturbance.

Since 1772, it was established that small bodies can stably orbit the same orbit as a planet, if it remains close to a Lagrange triangular point (also known as the “Trojan point”) which are located 60 ° in front of and 60° behind the planet in its orbit. Earth is the fourth planet with a Trojan asteroid (2010 TK7) after Jupiter, Mars and Neptune according to the date of its discovery This was difficult to locate due to the geometric positioning of the observation, it was discovered in 2010 thanks to NASA's WISE (Wide-Field Infrared Survey Explorer) telescope, but it was in April 2011 with the "Canada-France-Hawaii" telescope when its Trojan nature was confirmed, and its orbit is estimated to remain stable within next 10,000 years.

Earth, along with the Solar System, is located in the Milky Way galaxy, orbiting about 28,000 light-years from the center of the galaxy. It is currently about 20 light-years above the galaxy's equatorial plane, in Orion's spiral arm.

Stations and axial inclination

The stations occur on Earth due to the inclination of its rotation axis to the plane defined by its orbit (from the ecliptic). The illustration is winter in the northern hemisphere and summer in the southern hemisphere. (The distance and size between the bodies is not on a scale).

Due to the tilt of the Earth's axis, the amount of sunlight that reaches any point on the surface varies throughout the year. This causes seasonal changes in the climate, with summer in the northern hemisphere occurring when the North Pole is pointing towards the Sun, and winter when it points away. During the summer, the day length is longer and sunlight hits the surface more perpendicularly. During winter, the weather gets colder and the days get shorter. In the area of the Arctic Circle there is an extreme case of not receiving sunlight during part of the year; phenomenon known as polar night. In the southern hemisphere the same situation occurs but in reverse, with the orientation of the South Pole opposite to the direction of the North Pole.

The Earth and the Moon views from Mars, image of the Seas Reconnaissance Orbiter. From space, the Earth can be seen in phases similar to the lunar phases.

By astronomical convention, the four seasons are determined by solstices (points in the orbit at which the Earth's axis of rotation reaches its maximum inclination toward the Sun —summer solstice— or toward the opposite side —winter solstice—) and by equinoxes, when the tilt of the Earth's axis is perpendicular to the direction of the Sun. In the Northern Hemisphere, the winter solstice occurs around December 21, the summer solstice on June 21, the vernal equinox on June 20. March and the autumnal equinox on September 23. In the southern hemisphere the situation is reversed, with the summer and winter solstices on dates opposite to those in the northern hemisphere. The same happens with the spring and autumn equinoxes.

Earth's tilt angle is relatively stable over long periods of time. However, the inclination undergoes nutations; a slight irregular motion, with a period of 18.6 years. The orientation (rather than angle) of the Earth's axis also changes with time, precessing a full circle in every 25,800-year cycle. This precession is the reason for the difference between the sidereal year and the tropical year. Both motions are caused by the varying pull of the Sun and Moon on the Earth's equatorial bulge. From Earth's perspective, the poles also migrate a few meters above the surface. This polar motion has several cyclical components, which together are called quasiperiodic motions. In addition to the annual component of this movement, there is another movement with 14-month cycles called the Chandler wobble. The speed of the Earth's rotation also varies in a phenomenon known as day length variation.

In modern times, Earth's perihelion occurs around January 3 and aphelion around July 4. However, these dates change over time due to orbital precession and other factors, which follow cyclical patterns known as Milankovitch cycles. The variation in the distance between the Earth and the Sun results in an increase of about 6.9% of the solar energy that reaches the Earth at perihelion relative to aphelion. Since the southern hemisphere is tilted toward the Sun at the time the Earth comes closest to the Sun, throughout the year the southern hemisphere receives slightly more energy from the Sun than the northern hemisphere. However, this effect is much less important than the total energy change due to axial tilt, and most of this excess energy is absorbed by the ocean surface, which extends to a greater extent in the southern hemisphere.

Natural satellite and other orbital elements

Moon

The Moon is Earth's natural satellite. It is a relatively large Earth-like body: with a diameter of about a quarter of Earth's, it is the second largest satellite in the Solar System relative to the size of its planet, after its dwarf planet Pluto's satellite Charon.. The natural satellites that orbit the other planets are called "moons" in reference to Earth's Moon.

Details of the Earth-Luna system. In addition to the radius of each object, of the distance between them, and of the inclination of the axis of each one, the distance of the earth-Luna system's varnish to the center of the Earth is shown (4641 km). Images Archived on 1 November 2011 at Wayback Machine. and NASA information. The Moon's axis is located by Cassini's third law.

The gravitational pull between the Earth and the Moon causes the tides on Earth. The same effect on the Moon has given rise to its tidal coupling, which means that its period of rotation is identical to its period of translation around the Earth. As a result, the moon always presents the same face towards our planet. As the Moon orbits the Earth, different parts of its face are illuminated by the Sun, giving rise to lunar phases. The dark part of the face is separated from the light part of the solar terminator.

Due to tidal interaction, the Moon is receding from Earth at a rate of about 38 mm per year. Accumulated over millions of years, these small modifications, as well as the lengthening of the Earth day by around 23 µs, have produced significant changes. During the Devonian period, for example, (approximately 410 million years ago) a year had 400 days., each with a duration of 21.8 hours.

Sequence of images showing the rotation of the Earth and the translation of the Moon seen from the Galileo space probe.

The Moon may have dramatically affected the development of life, moderating the planet's climate. Paleontological evidence and computer simulations show that the tilt of the Earth's axis is stabilized by tidal interactions with the Moon. Some theorists believe that without this stabilization against the moment exerted by the Sun and the planets on the Earth's equatorial bulge, the axis of rotation could be chaotically unstable, showing chaotic changes over millions of years, as appears to be the case on Mars.

When viewed from Earth, the Moon is just such a distance away that the apparent size of its disk is nearly identical to that of the Sun. The angular diameter (or solid angle) of these two bodies coincides because although the diameter of the The Sun is about 400 times larger than the Moon, it is also 400 times more distant. This allows total and annular solar eclipses to occur on Earth.

The most widely accepted theory of the Moon's origin, the big impact theory, states that the Moon was formed by the collision of a Mars-sized protoplanet, called Tea, with early Earth. This hypothesis explains (among other things) the relative scarcity of iron and volatile elements on the Moon, and the fact that its composition is almost identical to that of the Earth's crust.

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  Representation at scale of the relative size and distance between the Earth and the Moon.

Other orbital elements

As of 2016, planet Earth has nine known natural quasi-satellites or co-orbital asteroids: (3753) Cruithne, the 2002 AA29, 2003 YN107, 2004 GU9, 2006 FV35, 2010 SO16, 2013 LX28, 2014 OL339, and 2016 HO3. On February 15, 2020, 2020 CD3 was discovered to be a temporary natural satellite of Earth.

As of September 2021, there are 4,550 operational man-made satellites orbiting the Earth.

Location of Earth

Diagram of our location within the observable universe. (Click here to see full screen.)

Livability

A planet that can support life is called habitable, even if no life originated on it. The Earth provides the (currently understood as) necessary conditions, such as liquid water, an environment that allows the assembly of complex organic molecules, and enough energy to maintain a metabolism. Other features are believed to also contribute to the planet's ability to originate and sustain life: the distance between the Earth and the Sun, as well as its orbital eccentricity, rotation speed, axial tilt, geological history, atmosphere permanence, and protection offered by the magnetic field.

Biosphere

It's called the "biosphere" the set of different types of life on the planet together with its physical environment, modified by the presence of the former. It is generally understood that the biosphere began to evolve 3.5 billion years ago. Earth is the only place where life is known to exist. The biosphere is divided into a series of biomes, inhabited by essentially similar plants and animals. On land, biomes are separated primarily by differences in latitude, height above sea level, and humidity. Terrestrial biomes located in the Arctic or Antarctic circles, at high altitudes, or in extremely arid areas are relatively barren of plant and animal life; species diversity is highest in humid lowlands, at equatorial latitudes.

Natural Resources and Land Use

The Earth provides resources that are exploited by humans for various purposes. Some of these are non-renewable resources, such as fossil fuels, which are hardly renewable in the short term.

Large deposits of fossil fuels are obtained from the earth's crust, consisting of coal, oil, natural gas and methane clathrates. These deposits are used by humans for energy production, and also as raw material for the production of chemicals. Ore bodies have also formed in the Earth's crust through various processes of mineralogenesis, as a consequence of erosion and processes involved in plate tectonics. These bodies harbor concentrated sources of various metals and other useful elements.

Earth's biosphere produces many useful biological products for humans, including (among many others) food, wood, pharmaceuticals, oxygen, and the recycling of much organic waste. The terrestrial ecosystem is dependent on topsoil and freshwater, and the oceanic ecosystem is dependent on dissolved nutrients from land. Humans also inhabit land using construction materials to build shelters. By 1993, land use by humans was approximately:

The amount of irrigated land in 1993 was estimated at 2,481,250 km².

Environment and risks

Large areas of the Earth's surface are subject to extreme weather conditions, such as tropical cyclones, hurricanes, or typhoons that dominate life in those areas. Many places are subject to earthquakes, landslides, tsunamis, volcanic eruptions, tornadoes, sinkholes, blizzards, floods, droughts, and other natural disasters.

Many specific areas are subject to man-made air and water pollution, acid rain, toxic substances, loss of vegetation (overgrazing, deforestation, desertification), loss of wildlife, species extinction, soil degradation and depletion, erosion and the introduction of invasive species.

According to the United Nations, there is a scientific consensus that links human activities to global warming, due to industrial emissions of carbon dioxide and anthropogenic waste heat. This is expected to lead to changes such as melting glaciers and frozen surfaces, more extreme temperatures, significant changes in climate, and global sea level rise.

Human Geography

Cartography —the study and practice of making maps—, and secondarily geography, have historically been the disciplines devoted to describing the Earth. Topography or determination of places and distances, and to a lesser extent navigation, or determination of position and direction, have been developed along with cartography and geography, providing and quantifying the necessary information.

The Earth has approximately 7,000,000,000 inhabitants as of October 2011. Projections indicated that the global human population would reach 7 billion by early 2012, but this figure was exceeded in mid-October 2011. and is expected to reach 9.2 billion by 2050. Most of this growth is thought to take place in developing countries. The sub-Saharan African region has the highest birth rate in the world. Population density varies greatly in different parts of the world, but the majority of the population lives in Asia. It is expected that by the year 2020, 60% of the world's population will be concentrated in urban areas, compared to 40% in rural areas.

It is estimated that only one eighth of the Earth's surface is suitable for human occupation; three quarters is covered by oceans, and half of the land surface is: desert (14%), high mountains (27%), or other less suitable terrain. The world's northernmost permanent settlement is Alert, on Ellesmere Island in Nunavut, Canada (82°28′N). The southernmost is the Amundsen-Scott Base, in Antarctica, almost exactly at the South Pole. (90°S)

Earth at night. Image composite from the lighting data of the DMSP/OLS, representing a simulated image of the night world. This image is not photographic and many features are brighter than it would look like a direct observer.

Independent sovereign nations lay claim to the entire land surface of the planet, except for parts of Antarctica and the unclaimed area of Bir Tawil between Egypt and Sudan. In the year 2011 there are 204 sovereign states, including the 192 member states of the United Nations. There are also 59 dependent territories, and a number of autonomous areas, disputed territories, and other entities. Historically, Earth has never had a sovereign government with authority over the entire world, although a number of nation-states have attempted to take over the world, to no avail.

The United Nations is a world intergovernmental organization that was created with the objective of intervening in disputes between nations, in order to avoid armed conflicts. However, it is not a world government. The UN primarily serves as a forum for diplomacy and international law. When the consensus of its members allows it, it provides a mechanism for armed intervention.

The first human to orbit the Earth was Yuri Gagarin on April 12, 1961. As of 2004, around 400 people had visited outer space and reached Earth's orbit. Of these, twelve have walked on the Moon. Under normal circumstances, the only humans in space are those on the International Space Station. The station's crew, currently made up of six people, is usually replaced every six months. The furthest human beings from Earth were 400,171 km, reached in the 1970s during the Apollo 13 mission.

Cultural perspective

The first photograph made by astronauts of the "love of the earth", taken from Apollo 8.

The word Earth comes from the Latin Tellus or Terra which was equivalent in Greek to Gea, name assigned to a deity, like the names of the other planets in the Solar System. The standard astronomical symbol for Earth consists of a cross circumscribed by a circle.

Unlike what happened with the rest of the planets in the Solar System, humanity did not begin to see the Earth as a moving object, in orbit around the Sun, until the century XVI. Earth has often been personified as a deity, in particular a goddess. In many cultures the mother goddess is also portrayed as a fertility goddess. In many religions, creation myths recall a story in which the Earth is created by a supernatural deity or deities. Various religious groups, often associated with fundamentalist branches of Protestantism or Islam, claim that their interpretations of these creation myths, recounted in their respective sacred texts, are the literal truth, and that they should be considered alongside scientific arguments. of the formation of the Earth and the development and origin of life, or even supersede them. Such claims are rejected by the scientific community and other religious groups. A prominent example is the controversy between creationism and evolution theory.

In the past there were various beliefs in a flat Earth, but this belief was displaced by the concept of a spherical Earth, due to observation and circumnavigation. The human perspective on the Earth has changed since the beginning of spaceflight, and the biosphere is now interpreted from an integrated global perspective. This is reflected in the growing environmental movement, which is concerned with humanity's effects on the planet.

Earth Day

In many countries, Earth Day is celebrated on April 22, with the aim of raising awareness of the planet's environmental conditions.