Image that Earth. Credit: NASA

Earth is an ocean planet. Our house world’s abundance of water — and life — provides it distinct in our solar system. Other planets, to add a few moons, have ice, atmospheres, seasons and also even weather, yet only on planet does the whole complicated mix come together in a method that urges life — and also lots of it.

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Earth is the 3rd planet native the Sun, and the densest and also fifth-largest of the eight planets in the Solar System. The is additionally the largest of the Solar System’s 4 terrestrial planets. It is sometimes referred to together the world or the Blue Planet.

Earth formed approximately 4.54 billion years ago, and life appeared on its surface within its an initial billion years. Earth’s biosphere climate significantly changed the atmospheric and also other an easy physical conditions, which enabled the proliferation that organisms as well as the development of the ozone layer, which in addition to Earth’s magnetic ar blocked harmful solar radiation, and also permitted formerly ocean-confined life to move safely to land. The physics properties the the Earth, as well as its geological background and orbit, have enabled life come persist. Approximates on how much longer the earth will have the ability to continue to support life range from 500 million year (myr), to as long as 2.3 billion years (byr).

Earth’s lithosphere is split into number of rigid segments, or tectonic plates, the migrate across the surface ar over periods of countless millions that years. About 71% that the surface is covered by salt water oceans, v the remainder consisting of continents and also islands which with each other have plenty of lakes and also other resources of water that add to the hydrosphere. Earth’s poles are mostly covered through ice that is the solid ice of the Antarctic ice sheet and also the sea ice the is the polar ice cream packs. The planet’s interior remains active, v a solid iron inner core, a liquid external core that generates the magnetic field, and also a special layer of reasonably solid mantle.

Earth gravitationally interacts with various other objects in space, especially the Sun and the Moon. During one orbit about the Sun, the earth rotates around its own axis 366.26 times, creating 365.26 solar days, or one sidereal year. The Earth’s axis of rotation is tilted 23.4° away from the perpendicular the its orbit plane, developing seasonal variations on the planet’s surface ar with a period of one tropical year (365.24 solar days).

The Moon is Earth’s only natural satellite. It began orbiting the Earth around 4.53 billion years ago (bya). The Moon’s gravitational interaction with earth stimulates s tides, stabilizes the axial tilt, and also gradually slows the planet’s rotation. The planet is house to millions of varieties of life, consisting of humans. Both the mineral resources of the planet and the products of the biosphere add resources that are supplied to assistance a worldwide human population. These occupants are grouped into around 200 independent can be fried states, which interact through diplomacy, travel, trade, and also military action. Human societies have arisen many views of the planet, consisting of its personification as a planetary deity, its form as flat, its place as the facility of the universe, and in the contemporary Gaia Principle, together a single, self-regulating biology in its very own right.

Formation the Earth

The more quickly material discovered in the Solar mechanism is date to 4.5672±0.0006 bya; therefore, the is inferred that the planet must have actually been formed by accretion approximately this time. Through 4.54±0.04 bya the primordial planet had formed. The formation and also evolution that the Solar mechanism bodies arisen in tandem with the Sun. In concept a solar nebula partitions a volume out of a molecular cloud by gravitational collapse, which starts to spin and also flatten into a circumstellar disk, and then the planets grow out of the in tandem v the star. A nebula contains gas, ice cream grains and also dust (including primordial nuclides). In nebular theory planetesimals commence creating as particulate accrues by cohesive clumping and also then by gravity. The assembly that the primordial planet proceeded for 10–20 myr. The Moon formed shortly thereafter, around 4.53 bya.

The Moon’s development remains debated. The functioning hypothesis is the it created by accretion from material loosed indigenous the earth after a Mars-sized object referred to as Theia influenced with Earth. The model, however, is not self-consistent. In this scenario, the fixed of Theia is 10% the the Earth’s mass, it impacts with the earth in a glancing blow, and also some that its massive merges through the Earth. Between roughly 3.8 and 4.1 bya, plenty of asteroid impacts throughout the Late hefty Bombardment caused significant changes to the better surface atmosphere of the Moon, and also by inference, come the Earth. Earth’s atmosphere and also oceans created by volcanic activity and outgassing that contained water vapor. The beginning of the world’s seas was condensation augmented by water and ice yielded by asteroids, proto-planets, and also comets. In this model, atmospheric “greenhouse gases” preserved the oceans from freezing while the newly creating Sun was only at 70% luminosity. By 3.5 bya, the Earth’s magnetic field was established, which assisted prevent the environment from being stripped far by the solar wind.

A crust developed when the molten outer layer of the planet planet cooled to type a solid together the gathered water vapor started to action in the atmosphere. The 2 models that describe land mass propose either a steady growth to the present-day develops or, an ext likely, a quick growth early on in Earth history followed by a long-term steady continent area. Continents developed by key tectonics, a process ultimately propelled by the continuous loss of warm from the earth’s interior. Top top time scale lasting hundreds of millions that years, the supercontinents have formed and also broken up three times. Approximately 750 mya (million years ago), one of the earliest recognized supercontinents, Rodinia, began to rest apart. The continents later on recombined to form Pannotia, 600–540 mya, then lastly Pangaea, which additionally broke apart 180 mya.


The form of the earth approximates one oblate spheroid, a ball flattened follow me the axis from pole to pole such the there is a bulge roughly the equator. This bulge results from the rotation of the Earth, and causes the diameter in ~ the equator to be 43 kilometres (kilometer) larger than the pole-to-pole diameter. Hence the furthest point on the surface ar from the Earth’s facility of mass is the Chimborazo volcano in Ecuador. The average diameter that the recommendation spheroid is about 12,742 km, which is around 40,000 km/π, as the meter was originally identified as 1/10,000,000 of the street from the equator come the north Pole with Paris, France.

Local topography deviates from this idealized spheroid, back on a worldwide scale, these deviations are small: planet has a yongin of around one component in about 584, or 0.17%, indigenous the referral spheroid, i beg your pardon is much less than the 0.22% tolerance permitted in billiard balls. The largest local deviations in the rocky surface of the planet are mountain Everest (8,848 m above local sea level) and also the Mariana Trench (10,911 m listed below local sea level). As result of the equatorial bulge, the surface areas farthest from the center of the planet are the summits of mount Chimborazo in Ecuador and Huascarán in Peru.

Chemical Composition

The mass of the planet is around 5.98×1024 kg. It is composed greatly of steel (32.1%), oxygen (30.1%), silicon (15.1%), magnesium (13.9%), sulfur (2.9%), nickel (1.8%), calcium (1.5%), and also aluminium (1.4%); v the remaining 1.2% consist of of trace quantities of various other elements. Because of mass segregation, the core an ar is believed to be mainly composed of iron (88.8%), through smaller amounts of nickel (5.8%), sulfur (4.5%), and also less than 1% map elements.

The geochemist F. W. Clarke calculated that a little an ext than 47% the the Earth’s crust is composed of oxygen. The more common absent constituents that the Earth’s late are virtually all oxides; chlorine, sulfur and fluorine space the only important exceptions to this and their full amount in any rock is usually much much less than 1%. The major oxides space silica, alumina, stole oxides, lime, magnesia, potash and soda. The silica features principally as an acid, forming silicates, and all the commonest minerals of igneous rocks are of this nature. From a computation based upon 1,672 analyses of every kinds the rocks, Clarke deduced that 99.22% were written of 11 oxides (see the table in ~ right), v the other constituents occurring in minute quantities.

Internal Structure

The interior of the Earth, like that of the other terrestrial planets, is separated into layers by your chemical or physical (rheological) properties, but unlike the other terrestrial planets, it has a unique outer and also inner core. The external layer of the planet is a chemically distinct silicate heavy crust, i m sorry is underlain through a very viscous hard mantle. The late is separated from the mantle through the Mohorovičić discontinuity, and the thickness the the crust varies: averaging 6 km (kilometers) under the oceans and also 30-50 kilometres on the continents. The crust and the cold, rigid, top of the top mantle are collectively known together the lithosphere, and it is that the lithosphere the the tectonic plates are comprised. In ~ the lithosphere is the asthenosphere, a fairly low-viscosity layer on i beg your pardon the lithosphere rides. Important alters in crystal framework within the mantle take place at 410 and also 660 km below the surface, spanning a transition zone the separates the upper and lower mantle. In ~ the mantle, very low viscosity liquid external core lies above a hard inner core. The inside core may rotate in ~ a slightly higher angular velocity 보다 the remainder the the planet, proceeding by 0.1–0.5° per year.

Earth cutaway from main point to exosphere. Not to scale. Credit: Wikipedia

Orbit and also Rotation

Earth’s rotation duration relative to the Sun—its median solar day—is 86,400 seconds of mean solar time (86,400.0025 SI seconds). As the Earth’s solar day is now slightly longer than that was throughout the 19th century because of tidal acceleration, each day varies between 0 and 2 SI multiple sclerosis longer.

Apart from meteors within the atmosphere and also low-orbiting satellites, the main obvious motion of celestial bodies in the Earth’s sky is come the west in ~ a rate of 15°/h = 15’/min. Because that bodies near the celestial equator, this is equivalent to an apparent diameter that the sun or Moon every 2 minutes; native the planet’s surface, the evident sizes of the Sun and the Moon are roughly the same.


Earth orbits the sun at an median distance of around 150 million kilometers every 365.2564 mean solar days, or one sidereal year. Native Earth, this gives an noticeable movement the the sunlight eastward v respect come the stars in ~ a rate of around 1°/day, which is one noticeable Sun or Moon diameter every 12 hours. As result of this motion, on median it take away 24 hours—a solar day—for earth to complete a complete rotation around its axis so the the sunlight returns to the meridian. The orbital speed of the planet averages about 29.8 km/s (107,000 km/h), which is fast enough to take trip a street equal to the planet’s diameter, about 12,742 km, in 7 minutes, and also the distance to the Moon, 384,000 km, in about 3.5 hours.

The Moon revolves v the Earth around a usual barycenter every 27.32 days family member to the background stars. When combined with the Earth–Moon system’s common transformation around the Sun, the period of the synodic month, from new moon to brand-new moon, is 29.53 days. Perceived from the celestial phibìc pole, the motion of Earth, the Moon and their axial rotations room all counterclockwise. Perceived from a vantage point over the north poles of both the Sun and also the Earth, the earth revolves in a counterclockwise direction around the Sun. The orbital and also axial planes are not exactly aligned: earth’s axis is tilted part 23.4 levels from the perpendicular to the Earth–Sun plane (the ecliptic), and also the Earth–Moon airplane is tilted approximately ±5.1 degrees versus the Earth–Sun plane. Without this tilt, there would certainly be one eclipse every 2 weeks, alternate between lunar eclipses and solar eclipses.

The Hill sphere, or gravitational round of influence, that the planet is around 1.5 Gm or 1,500,000 kilometres in radius. This is the maximum street at which the Earth’s gravitational influence is stronger than the more distant Sun and planets. Objects have to orbit the earth within this radius, or castle can become unbound by the gravitational perturbation that the Sun.

Earth, together with the Solar System, is located in the Milky means galaxy and orbits around 28,000 light years native the center of the galaxy. It is currently around 20 light years over the galactic plane in the Orion spiral arm.

Earth’s axial tilt (or obliquity) and also its relationship to the rotation axis and airplane of orbit. Credit: NASA

Axis Tilt and Seasons

Due come the axial tilt the the Earth, the amount of sunlight reaching any given point on the surface varies end the course of the year. This reasons seasonal readjust in climate, v summer in the northern hemisphere emerging when the phibìc Pole is pointing toward the Sun, and also winter taking place when the pole is sharp away. During the summer, the work lasts longer and also the sun climbs greater in the sky. In winter, the climate becomes typically cooler and the days shorter. Above the Arctic Circle, an extreme case is reached where there is no daylight at all for component of the year—a polar night. In the southern hemisphere the case is specifically reversed, v the south Pole oriented opposite the direction the the phibìc Pole.

By huge convention, the four seasons are figured out by the solstices—the allude in the orbit of best axial tilt towards or away from the Sun—and the equinoxes, as soon as the direction the the tilt and also the direction to the Sun space perpendicular. In the north hemisphere, Winter Solstice occurs on about December 21, Summer Solstice is near June 21, feather Equinox is about March 20 and also Autumnal Equinox is about September 23. In the southerly hemisphere, the situation is reversed, v the Summer and also Winter Solstices exchanged and the Spring and Autumnal Equinox days switched.

The edge of the Earth’s tilt is fairly stable over long periods the time. The tilt does undergo nutation; a slight, irregular movement with a main period of 18.6 years. The orientation (rather than the angle) of the Earth’s axis likewise changes end time, precessing around in a finish circle end each 25,800 year cycle; this precession is the factor for the difference between a sidereal year and also a tropic year. Both that these motions are resulted in by the varying attraction the the Sun and also Moon top top the Earth’s equatorial bulge. Native the view of the Earth, the poles additionally migrate a few meters across the surface. This polar motion has multiple, cyclical components, which jointly are termed quasiperiodic motion. In addition to an annual component come this motion, there is a 14-month cycle referred to as the Chandler wobble. The rotational velocity of the Earth additionally varies in a phenomenon known as length of work variation.

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In modern times, Earth’s perihelion occurs around January 3, and the aphelion roughly July 4. This dates adjust over time due to precession and also other orbital factors, which monitor cyclical patterns known as Milankovitch cycles. The an altering Earth–Sun distance causes boost of about 6.9% in solar power reaching the earth at perihelion family member to aphelion. Due to the fact that the southerly hemisphere is tilted toward the sun at around the same time that the planet reaches the closest strategy to the Sun, the southern hemisphere obtain slightly more energy native the sun than does the northern over the course of a year. This impact is much less far-reaching than the full energy adjust due to the axial tilt, and also most the the excess energy is soaked up by the higher proportion the water in the southerly hemisphere.