地球的未來 可以由幾個地球長期的轉變估計，包括地球表面的化學狀態,地球內部冷卻的速度, 與其他太陽系行星的攝動,以及太陽光度穩定的增長。當中不明朗的人為因素, 如地球工程的技術,[2] 導致地球明顯的變化。[3][4] 目前的生態危機[5] 主要是由人類科技發展導致[6]而其影響可能會持續長達500萬年。[7]科技發展亦可能導致人類滅絕, 使地球回復到緩慢的進化步伐及長期的自然過程。[8][9]
數百萬年之間，隨機的天體事件構成了全球性生物圈的風險，這可能會導致物種大滅絕 。這些天體事件包括100光年內的超新星爆發，直徑為5-10公里（3.1〜6.2英里）以上的彗星或小行星。其他大型地質事件更具可預測性。如果忽視全球暖化的長期影響， 米蘭科維奇循環 估計地球將會繼續處於冰期至少到第四紀冰河時期結束。這是由地球軌道的離心, 轉軸傾角及進動現象的因素導致。[10]隨着超大陸旋迴的進行, 地球板塊將可能在2.5至3.5億年間形成一個超大陸。在1.5-4.5億年後, 地球的轉軸傾角可能出現最多90度的變化。
約1.1億年後，太陽光度將高於目前10％。 這足以令大氣層成為「溫室」，使海水大量蒸發。在之後的3億年，太陽的亮度將穩步增加，導致地球的太陽輻射上升。這將導致減少在大氣中的二氧化碳水平。在6億年內，大氣中二氧化碳的濃度將低於維持C3類植物光合作用所需的水平。 C4類植物雖然能在二氧化碳濃度低至數百萬分之十的環境下生存，但長期來說地球的植物是趨向滅亡，而動物也會因欠缺氧氣的補充在數百萬年後滅種。[11][12]
地球最有可能的命運是，7.5億年後進入紅巨星階段的太陽膨脹到地球的軌道，並把地球吸收。
人類活動的影響
人類對地球生物圈有關鍵影響, 其龐大的人口主導着地球上許多生態系統。[3]現階段人類活動已經產生了地球表面顯著的變化。超過三分之一的土地面積被人類改動，並使用了全球約20％的初級生產。[4]工業革命以來，大氣中二氧化碳的濃度增加了近30％。[3] 這導致了廣泛及持續的物種滅絕，總稱為全新世滅絕事件。自20世紀50年代以來，人類活動所造成的大規模物種滅絕佔總物種數約10％(截至2007年)。[6]目前大約有30％的物種有在未來一百年內滅絕的危機。[13] 現代的物種滅絕事件主要是棲息地的破壞, 廣泛分佈的入侵物種, 人類的狩獵活動及氣候變化的結果。[14][15]物種滅絕的後果會持續至少500萬年。[7]這可能會導致地球生態的生物多樣性下降。
目前有多個已知可對人類生存造成威脅甚至使人類滅亡的危機。這些由人類自身造成的危機包括奈米科技的誤用、核戰爭、基因工程造成的疾病，或由一些物理實驗所造成的大型災難。 同樣，一些自然事件可能造成世界末日的威脅, 包括致命性的疾病, 小行星或彗星的撞擊事件，失控的溫室效應及資源枯竭。然而，計算這些情況發生的實際可能性十分困難。[8][9]
如果人類滅絕，人類建造的各樣建築物將開始腐爛。大型建築物的半衰期估計約為1000年。能存在最長時間的建築物有可能是露天礦場、大型垃圾填埋場、運河、主要公路及大型水壩。一萬年後，幾個巨大的石碑如吉薩金字塔群或拉什莫爾山雕塑仍可能以某種形式生存。[9]
隨機事件
由於太陽繞銀河系，隨機移動的恆星若足夠地接近，會對太陽系有破壞性的影響。[16]密切的恆星相遇可能導致奧爾特雲彗星的拱點顯著減少。[17]這樣可以觸達到太陽系內的彗星數量40倍的增長。從這些彗星的影響，可以引發大規模滅絕地球上的生命。這些災難發生平均每4500萬年一次。[18] The mean time for the 太陽 to collide with another star in the solar neighborhood is approximately Template:現在rap, which is much longer than the 估計 年齡 of the Milky Way galaxy, at Template:現在rap. This can be taken as an indication of the low likelihood of such an event occurring during the lifetime of the 地球.[19]
直徑為5-10公里（3.1〜6.2英里）或更大的小行星或彗星的撞擊能量足以釋放一個全球性的生態災難及導致物種滅絕的數量顯著的上升。由大型撞擊事件造成的另一個不利影響是使灰塵籠罩地球，在一周之內降低陸地溫度約15°C 及停止光合作用幾個月。大型撞擊事件 is 估計 to be at least 100 million 年. During the last 540 million 年, simulations demonstrated that such an impact rate is sufficient to 導致 5–6 mass extinctions and 20–30 lower severity events. This matches the geologic record of significant extinctions during the Phanerozoic era. Such events can be expected to continue into the 未來.[20]
A supernova is a cataclysmic explosion of a star. Within the Milky Way galaxy, supernova explosions occur on aver年齡 once every 30 年. During the history of the 地球, multiple such events have likely occurred within a distance of 100 light 年. Explosions inside this distance can contaminate the 地球 with radioisotopes and possibly impact the biosphere.[21] Gamma rays emitted by a supernova react with nitrogen in the atmosphere, producing nitrous oxides. These molecules 導致 a depletion of the ozone layer that protects the surface from ultraviolet radiation from the 太陽. An 上升 in UV-B radiation of only 10–30% is sufficient to 導致 a significant impact to life; particularly to the phytoplankton that form the base of the 海洋ic food chain. A supernova explosion at a distance of 26 light 年 將會 reduce the ozone column density by half. On aver年齡, a supernova explosion occurs within 32 light 年 once every few hundred million 年, resulting in a depletion of the ozone layer lasting several centuries.[22] Over the next two 十億 年, there 將會 be about 20 supernova explosions and one gamma ray burst that 將會 have a significant impact on the 地球's biosphere.[23]
The incremental effect of gravitational perturbations between the 地球s 導致s the inner 太陽系 as a whole to behave chaotically over long time periods. This does not significantly affect the stability of the 太陽系 over intervals of a few millions 年 or less, but over 十億s of 年 the orbits of the 地球s become unpredictable. Computer simulations of the 太陽系 's evolution over the next five 十億 年 suggest that there is a small (less than 1%) chance that a collision could occur between 地球 and either Mercury, Venus, or Mars.[24][25] During the same interval, the odds that the 地球 將會 be scattered out of the 太陽系 by a passing star are on the order of one part in 105. In such a scenario, the 海洋s would freeze solid within a several million 年, leaving only a few pockets of liquid water about 14 km（8.7 mi） underground. There is a remote chance that the 地球 將會 instead be captured by a passing binary star system, allowing the 地球's biosphere to remain intact. The odds of this happening are about one chance in three million.[26]
軌道和轉軸
The gravitational perturbations of the other 地球s in the 太陽系 combine to modify the orbit of the 地球 and the orientation of its spin axis. These 改變 can influence the 地球ary climate.[10][27][28][29]
Historically, there have been cyclical ice 年齡s in which glacial sheets periodically covered the higher latitudes of the continents. Ice 年齡s may occur be導致 of 改變 in 海洋 circulation and continentality induced by plate tectonics.[30] The Milankovitch theory predicts that glacial periods occur during ice 年齡s be導致 of astronomical factors in combination with climate feedback mechanisms. The primary astronomical drivers are a higher than normal orbital eccentricity, a low axial tilt (or obliquity), and the alignment of summer solstice with the aphelion.[10] Each of these effects occur cyclically. For example, the eccentricity 改變 over time cycles of about 100,000 and 400,000 年, with the value ranging from less than 0.01 up to 0.05.[31][32] This is equivalent to a 改變 of the semiminor axis of the 地球's orbit from 99.95% of the semimajor axis to 99.88%, respectively.[33]
The 地球 is passing through an ice 年齡 k現在n as the quaternary glaciation, and is presently in the Holocene interglacial period. This period would normally be expected to end in about 25,000 年.[29] However, the 上升d rate of carbon dioxide release into the atmosphere by 人類s may delay the onset of the next glacial period until at least 50,000–130,000 年 from 現在. However, a global warming period of finite duration (based on the assumption that fossil fuel use 將會 cease by the 年 2200) 將會 probably only impact the glacial period for about 5,000 年. Thus, a brief period of global warming induced through a few centuries worth of greenhouse gas emission would only have a limited impact in the long term.[10]
The tidal acceleration of the Moon slows the rotation rate of the 地球 and 上升s the 地球-Moon distance. Friction effects—between the core and mantle and between the atmosphere and surface—can dissipate the 地球's rotational energy. These combined effects are expected to 上升 the length of the day by more than 1.5 hours over the next 250 million 年, and to 上升 the obliquity by about a half degree. The distance to the Moon 將會 上升 by about 1.5 地球 radii during the same period.[34]
Based on computer models, the presence of the Moon appears to stabilize the obliquity of the 地球, which may help the 地球 to avoid dramatic climate 改變 .[35] This stability is achieved be導致 the Moon 上升s the precession rate of the 地球's spin axis, thereby avoiding resonances between the precession of the spin and precession frequencies of the ascending node of the 地球's orbit.[36] (That is, the precession motion of the ecliptic.) However, as the semimajor axis of the Moon's orbit continues to 上升 in the 未來, this stabilizing effect 將會 diminish. At some point perturbation effects 將會 probably 導致 chaotic variations in the obliquity of the 地球, and the axial tilt may 改變 by angles as high as 90° from the plane of the orbit. This is expected to occur within about 1.5–4.5 十億 年, although the exact time is unk現在n.[37]
A high obliquity would probably result in dramatic 改變 in the climate and may destroy the 地球's habitability.[28] When the axial tilt of the 地球 reaches 54°, the equator 將會 receive less radiation from the 太陽 than the poles. The 地球 could remain at an obliquity of 60° to 90° for periods as long as 10 million 年.[38]
地球動力學
Tectonics-based events 將會 continue to occur well into the 未來 and the surface 將會 be steadily reshaped by tectonic uplift, extrusions, and erosion. Mount Vesuvius can be expected to erupt about 40 times over the next 1,000 年. During the same period, about five to seven 地球quakes of magnitude 8 or greater should occur along the San Andreas Fault, while about 50 magnitude 9 events may be expected 世界wide. Mauna Loa should experience about 200 eruptions over the next 1,000 年, and the Old Faithful Geyser 將會 likely cease to operate. The Niagara Falls 將會 continue to retreat upstream, reaching Buffalo in about 30,000–50,000 年.[9]
In 10,000 年, the post-glacial rebound of the Baltic Sea 將會 have reduced the depth by about 90米（300英尺）. The Hudson Bay 將會 下降 in depth by 100 m over the same period.[25] After 100,000 年, the island of Hawaii 將會 have shifted about 9 km（5.6 mi） to the northwest. The 地球 may be entering another glacial period by this time.[9]
The theory of plate tectonics demonstrates that the continents of the 地球 are moving across the surface at the rate of a few centimeters per 年. This is expected to continue, causing the plates to relocate and collide. Continental drift is facilitated by two factors: the energy generation within the 地球 and the presence of a hydrosphere. With the loss of either of these, continental drift 將會 come to a halt.[39] The production of heat through radiogenic processes is sufficient to maintain mantle convection and plate subduction for at least the next 1.1 十億 年.[40]
At present, the continents of North and South America are moving westward from Africa and Europe. Researchers have produced several scenarios about how this 將會 continue in the 未來.[41] These geodynamic models can be distinguished by the subduction flux, whereby the 海洋ic crust moves under a continent. In the introversion model, the younger, interior, Atlantic 海洋 becomes preferentially subducted and the current migration of North and South America is reversed. In the extroversion model, the older, exterior, Pacific 海洋 remains preferentially subducted and North and South America migrate toward eastern Asia.[42][43]
As the understanding of geodynamics improves, these models 將會 be subject to revision. In 2008, for example, a computer simulation was used to predict that a reorganization of the mantle convection 將會 occur, causing a supercontinent to form around Antarctica.[44]
Regardless of the outcome of the continental migration, the continued subduction process 導致s water to be transported to the mantle. After a 十億 年 from the present, a geophysical model gives an 估計 that 27% of the current 海洋 mass 將會 have been subducted. If this process were to continue unmodified into the 未來, the subduction and release would reach a point of stability after 65% of the current 海洋 mass has been subducted.[45]
Christopher Scotese and his colleagues have mapped out the predicted motions several hundred million 年 into the 未來 as part of the Paleomap Project.[41] In their scenario, 50 million 年 from 現在 the Mediterranean sea may vanish and the collision between Europe and Africa 將會 create a long mountain range extending to the current location of the Persian Gulf. Australia 將會 merge with Indonesia, and Baja California 將會 slide northward along the coast. New subduction zones may appear off the eastern coast of North and South America, and mountain chains 將會 form along those coastlines. To the south, the migration of Antarctica to the north 將會 導致 all of its ice sheets to melt. This, along with the melting of the Greenland ice sheets, 將會 raise the aver年齡 海洋 level by 90米（300英尺）. The inland flooding of the continents 將會 result in climate 改變 .[41]
As this scenario continues, by 100 million 年 from the present the continental spreading 將會 have reached its maximum extent and the continents 將會 then begin to coalesce. In 250 million 年, North America 將會 collide with Africa while South America 將會 wrap around the southern tip of Africa. The result 將會 be the formation of a new supercontinent (sometimes called Pangaea Ultima), with the Pacific 海洋 stretching across half the 地球. The continent of Antarctica 將會 reverse direction and return to the South Pole, building up a new ice cap.[46]
The first scientist to extrapolate the current motions of the continents was Canadian geologist Paul F. Hoffman of Harvard University. In 1992, Hoffman predicted that the continents of North and South America would continue to advance across the Pacific 海洋, pivoting about Siberia until they begin to merge with Asia. He dubbed the resulting supercontinent, Amasia.[47][48] Later, in the 1990s, Roy Livermore calculated a similar scenario. He predicted that Antarctica would start to migrate northward, and east Africa and Madagascar would move across the Indian 海洋 to collide with Asia.[49]
In an extroversion model, the closure of the Pacific 海洋 would be complete in about 350 million 年.[50] This marks the completion of the current supercontinent cycle, wherein the continents split apart and then rejoin each other about every 400–500 million 年.[51] Once the supercontinent is built, plate tectonics may enter a period of inactivity as the rate of subduction drops by an order of magnitude. This period of stability could 導致 an 上升 in the mantle temperature at the rate of 30—100 K-改變[convert: 不明單位] every 100 million 年, which is the minimum lifetime of past supercontinents. As a consequence, volcanic activity may 上升.[43][50]
The formation of a supercontinent can dramatically affect the environment. The collision of plates 將會 result in mountain building, thereby shifting weather patterns. Sea levels may fall be導致 of 上升d glaciation.[52] The rate of surface weathering can rise, resulting in an 上升 in the rate that organic material is buried. Supercontinents can 導致 a drop in global temperatures and an 上升 in atmospheric oxygen. This, in turn, can affect the climate, further lowering temperatures.[53] All of these 改變 can result in more rapid biological evolution as new niches emerge.
The formation of a supercontinent insulates the mantle. The flow of heat 將會 be concentrated, resulting in volcanism and the flooding of large areas with basalt. Rifts 將會 form and the supercontinent 將會 split up once more.[54] The 地球 may then experience a warming period, as occurred during the Cretaceous period.[53]
The iron-rich core region of the 地球 is divided into a 1,220 km（760 mi） radius solid inner core and a 3,480 km（2,160 mi） radius liquid outer core.[55] The rotation of the 地球 creates convective eddies in the outer core region that 導致 it to function as a dynamo.[56] This generates a magnetosphere about the 地球 that deflects particles from the solar wind, which prevents significant erosion of the atmosphere from sputtering. As heat from the core is transferred outward toward the mantle, the net trend is for the inner boundary of the liquid outer core region to freeze, thereby releasing thermal energy and causing the solid inner core to grow.[57] This iron crystallization process has been ongoing for about a 十億 年. In the modern era, the radius of the inner core is expanding at an aver年齡 rate of roughly 0.5 mm（0.02英寸） per 年, at the expense of the outer core.[58] Nearly all of the energy needed to power the dynamo is being supplied by this process of inner core formation.[59]
The growth of the inner core may be expected to consume most of the outer core by some 3–4 十億 年 from 現在, resulting in a nearly solid core composed of iron and other heavy elements. The surviving liquid envelope 將會 mainly consist of lighter elements that 將會 undergo less mixing.[60] Alternatively, if at some point plate tectonics comes to an end, the interior 將會 cool less efficiently, which may end the growth of the inner core. In either case, this can result in the loss of the magnetic dynamo. Without a functioning dynamo, the magnetic field of the 地球 將會 decay in a geologically short time period of roughly 10,000 年.[61] The loss of the magnetosphere 將會 導致 an 上升 in erosion of light elements, particularly hydrogen, from the 地球's outer atmosphere into space, resulting in less favorable conditions for life.[62]
太陽的演變
The energy generation of the 太陽 is based upon thermonuclear fusion of hydrogen into helium. This occurs in the core region of the star using the proton–proton chain reaction process. Be導致 there is no convection in the solar core, the helium concentration builds up in that region without being distributed throughout the star. The temperature at the core of the 太陽 is too low for nuclear fusion of helium atoms through the triple-alpha process, so these atoms do not contribute to the net energy generation that is needed to maintain hydrostatic equilibrium of the 太陽.[63]
At present, nearly half the hydrogen at the core has been consumed, with the remainder of the atoms consisting primarily of helium. As the number of hydrogen atoms per unit mass 下降, so too does their energy output provided through nuclear fusion. This results in a 下降 in pressure support, which 導致s the core to contract until the 上升d density and temperature bring the core pressure in to equilibrium with the layers above. The higher temperature 導致s the remaining hydrogen to undergo fusion at a more rapid rate, thereby generating the energy needed to maintain the equilibrium.[63]
.svg)
The result of this process has been a steady 上升 in the energy output of the 太陽. When the 太陽 first became a main sequence star, it radiated only 70% of the current luminosity. The luminosity has 上升d in a nearly linear fashion to the present, rising by 1% every 110 million 年.[65] Likewise, in three 十億 年 the 太陽 is expected to be 33% more luminous. The hydrogen fuel at the core 將會 finally be exhausted in 4.8 十億 年, when the 太陽 將會 be 67% more luminous than at present. Thereafter the 太陽 將會 continue to burn hydrogen in a shell surrounding its core, until the 上升 in luminosity reaches 121% of the present value. This marks the end of the 太陽's main sequence lifetime, and thereafter it 將會 pass through the subgiant st年齡 and evolve into a red giant.[1]
With the 上升d surface area of the 太陽, the amount of energy emitted 將會 上升. The global temperature of the 地球 將會 climb be導致 of the rising luminosity of the 太陽, the rate of weathering of silicate minerals 將會 上升. This in turn 將會 下降 the level of carbon dioxide in the atmosphere. Within the next 600 million 年 from the present, the concentration of CO
2 將會 fall below the critical threshold needed to sustain C3 photosynthesis: about 50 parts per million. At this point, trees and forests in their current forms 將會 no longer be able to survive.[66] However, C4 carbon fixation can continue at much lower concentrations, down to above 10 parts per million. Thus plants using Template:C4 photosynthesis may be able to survive for at least 0.8 十億 年 and possibly as long as 1.2 十億 年 from 現在, after which rising temperatures 將會 make the biosphere unsustainable.[67][68][69] Currently, Template:C4 plants represent about 5% of 地球's plant biomass and 1% of its k現在n plant species.[70] For example, about 50% of all grass species (Poaceae) use the Template:C4 photosynthetic pathway,[71] as do many species in the herbaceous family Amaranthaceae.[72]
When the levels of carbon dioxide fall to the limit where photosynthesis is barely sustainable, the proportion of carbon dioxide in the atmosphere is expected to oscillate up and down. This 將會 allow land vegetation to flourish each time the level of carbon dioxide rises due to tectonic activity and animal life. However, the long term trend is for the plant life on land to die off altogether as most of the remaining carbon in the atmosphere becomes sequestered in the 地球.[73] Some microbes are capable of photosynthesis at concentrations of CO
2 of a few parts per million, so these life forms would probably disappear only be導致 of rising temperatures and the loss of the biosphere.[67] The loss of plant life 將會 also result in the eventual loss of oxygen and with it the death of animals; the first animals to disappear would be large mammals followed by small mammals and birds, amphibians, reptiles, and finally invertebrates.[74]
In their work The Life and Death of 地球 地球, authors Peter D. Ward and Donald Brownlee have also argued that some form of animal life may continue even after most of the 地球's plant life has disappeared. Initially, they expect that some insects, lizards, birds and small mammals may persist, along with sea life. Without oxygen replenishment by plant life, however, they believe that the animals would probably die off from asphyxiation within a few million 年. Even if sufficient oxygen were to remain in the atmosphere through the persistence of some form of photosynthesis, the steady rise in global temperature would result in a gradual loss of biodiversity. As temperatures continue to rise, the last animal life 將會 inevitably be driven back toward the poles, terrestrial food chains 將會 become fungus-based, and many of these animals 將會 become simpler but tougher in body structure. Much of the surface would become a barren desert and life would primarily be found in the 海洋s[73]; however, due also to a 下降 of the amount or organic matter coming to the 海洋s from the land, life would disappear too there following a similar path to that on 地球's surface with invertebrates being the last living animals[74]. As a result of these processes, multi-cellular lifeforms may be extinct in about 800 million 年, and eukaryotes in 1.3 十億 年 from 現在, leaving only the prokaryotes.[75]
By one 十億 年 from 現在, about 27% of the modern 海洋 將會 have been subducted into the mantle. If this process were allowed to continue uninterrupted, it would reach an equilibrium state where 65% of the current surface reservoir would remain at the surface.[76] Once the solar luminosity is 10% higher than its current value, the aver年齡 global surface temperature 將會 rise to 320 K（47 °C）. The atmosphere 將會 become a "moist greenhouse" leading to a runaway evaporation of the 海洋s.[77][78] At this point, models of the 地球's 未來 environment demonstrate that the stratosphere would contain 上升 levels of water. These water molecules 將會 be broken down through photodissociation by solar ultraviolet radiation, allowing hydrogen to escape the atmosphere. The net result would be a loss of the 世界's sea water by about 1.1 十億 年 from the present.[79][80]
In this 海洋-free era, there 將會 continue to be reservoirs at the surface as water is steadily released from the deep crust and mantle[45], where it's 估計 there's an amount of water equivalent to several times the currently present on 地球's 海洋s[81]. Some water may be retained at the poles and there may be occasional rainstorms, but for the most part the 地球 would be a dry desert. Even in these arid conditions, the 地球 may retain some microbial and possibly even multi-cellular life.[78] Most of these microbes 將會 be halophiles. However, the 上升ly extreme conditions 將會 likely lead to the extinction of the prokaryotes between 1.6 十億 年[75] and 2.8 十億 年 [74] from 現在, with the last of them living in residual ponds of water at high latitudes and heights or in caverns with trapped ice; underground life, however, could last longer[74]. What happens next depends on the level of tectonic activity. A steady release of carbon dioxide by volcanic eruption could eventually 導致 the atmosphere to enter a "supergreenhouse" state like that of the 地球 Venus. But without surface water, plate tectonics would probably come to a halt and most of the carbonates would remain securely buried[82] until the 太陽 became a red giant and its 上升 on luminosity heated them releasing the carbon dioxide.[81]
The loss of the 海洋s could be delayed until two 十億 年 in the 未來 if the total atmospheric pressure were to decline. A lower atmospheric pressure would reduce the greenhouse effect, thereby lowering the surface temperature. This could occur if natural processes were to remove the nitrogen from the atmosphere. Studies of organic sediments has shown that at least 100千帕斯卡（0.99標準大氣壓） of nitrogen has been removed from the atmosphere over the past four 十億 年; enough to effectively double the current atmospheric pressure if it were to be released. This rate of removal would be sufficient to counter the effects of 上升 solar luminosity for the next two 十億 年. However, beyond that point, unless most of 地球's surface water has been lost by that time, in which case the 地球 將會 stay in the same conditions until the starting of the red giant phase[78], the amount of water in the lower atmosphere 將會 have risen to 40% and the runaway moist greenhouse 將會 commence[83] when the luminosity from the 太陽 reaches 35–40% more than its current value, 3–4 十億 年 from 現在.[79] The atmosphere 將會 heat up and the surface temperature 將會 rise sufficiently to melt surface rock.[80][78] However, most of the atmosphere 將會 be retained until the 太陽 has entered the red giant st年齡[84]
Once the 太陽 改變 from burning hydrogen at its core to burning hydrogen around its shell, the core 將會 start to contract and the outer envelope 將會 expand. The total luminosity 將會 steadily 上升 over the following 十億 年 until it reaches 2,730 times the 太陽's current luminosity at the 年齡 of 12.167 十億 年. During this phase the 太陽 將會 experience more rapid mass loss, with about 33% of its total mass shed with the solar wind. The loss of mass 將會 mean that the orbits of the 地球s 將會 expand. The orbital distance of the 地球 將會 上升 to at most 150% of its current value.[65]
The most rapid part of the 太陽's expansion into a red giant 將會 occur during the final st年齡s, when the 太陽 將會 be about 12 十億 年 old. It is likely to expand to swallow both Mercury and Venus, reaching a maximum radius of 1.2 AU（180,000,000 km）. The 地球 將會 interact tidally with the 太陽's outer atmosphere, which would serve to 下降 地球's orbital radius. Drag from the chromosphere of the 太陽 would also reduce the 地球's orbit. These effects 將會 act to counterbalance the effect of mass loss by the 太陽, and the 地球 將會 most likely be engulfed by the 太陽.[65] The ablation and vaporization 導致d by its fall on a decaying trajectory towards the 太陽 將會 remove 地球's crust and mantle, then finally destroy it after at most 200 年.[85] 地球's sole legacy 將會 be a very slight 上升 (0.01%) of the solar metallicity.[86]
Before this happens, most of 地球's atmosphere 將會 have been lost to space and its surface 將會 consist of a magma 海洋 with floating continents of metals and metal oxides as well as icebergs of refractory materials, with its surface temperature reaching more than 2,400 K（2,130 °C）. [87]
The drag from the solar atmosphere may 導致 the orbit of the Moon to decay. Once the orbit of the Moon closes to a distance of 18,470 km（11,480 mi）, it 將會 cross the 地球's Roche limit. Tidal interaction with the 地球 would then break apart the Moon, turning it into a ring system. Most of the orbiting ring 將會 then begin to decay, and the debris 將會 impact the 地球. Hence, even if the 地球 is not swallowed up by the 太陽, the 地球 may be left moonless.[88]
See also
- History of the 地球
- Timeline of the far 未來
- Habitable zone
- 地球ary engineering
- 地球ary habitability
- Risks to civilization, 人類s and 地球 地球
- Stability of the 太陽系
- Eschatology
References
Further reading
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