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Estimates on how much longer the planet will be able to continue to support life range from 500 million years (myr), to as long as 2.3 billion years (byr).[184][185][186] The future of the planet is closely tied to that of the Sun. As a result of the steady accumulation of helium at the Sun's core, the star's total luminosity will slowly increase. The luminosity of the Sun will grow by 10% over the next 1.1 byr and by 40% over the next 3.5 byr.[187] Climate models indicate that the rise in radiation reaching the Earth is likely to have dire consequences, including the loss of the planet's oceans.[188] The Earth's increasing surface temperature will accelerate the inorganic CO2 cycle, reducing its concentration to levels lethally low for plants (10 ppm for C4 photosynthesis) in approximately 500-900 myr.[184] The lack of vegetation will result in the loss of oxygen in the atmosphere, so animal life will become extinct within several million more years.[189] After another billion years all surface water will have disappeared[185] and the mean global temperature will reach 70 °C[189] (158 °F). The Earth is expected to be effectively habitable for about another 500 myr from that point,[184] although this may be extended up to 2.3 byr if the nitrogen is removed from the atmosphere.[186] Even if the Sun were eternal and stable, 27% of the water in the modern oceans will descend to the mantle in one billion years, due to reduced steam venting from mid-ocean ridges.[190] 14 billion year timeline showing Sun's present age at 4.6 byr; from 6 byr Sun gradually warming, becoming a red dwarf at 10 byr, "soon" followed by its transformation into a white dwarf star The life cycle of the Sun The Sun, as part of its evolution, will become a red giant in about 5 byr. Models predict that the Sun will expand out to about 250 times its present radius, roughly 1 AU (150,000,000 km).[187][191] Earth's fate is less clear. As a red giant, the Sun will lose roughly 30% of its mass, so, without tidal effects, the Earth will move to an orbit 1.7 AU (250,000,000 km) from the Sun, when the star reaches its maximum radius. The planet was, therefore, initially expected to escape envelopment by the expanded Sun's sparse outer atmosphere, though most, if not all, remaining life would have been destroyed by the Sun's increased luminosity (peaking at about 5,000 times its present level).[187] A 2008 simulation indicates that the Earth's orbit will decay due to tidal effects and drag, causing it to enter the red giant Sun's atmosphere and be vaporized.[191] After that, the Sun's core will collapse into a white dwarf, as its outer layers are ejected into space as a planetary nebula. The matter that once made up the Earth will be released into interstellar space, where it may one day become incorporated into a new generation of planets and other celestial bodies. |
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