<P> Earth's expected long - term future is closely tied to that of the Sun . Over the next 7000110000000000000 ♠ 1.1 Bys, solar luminosity will increase by 10%, and over the next 7000350000000000000 ♠ 3.5 Bys by 40% . The Earth's increasing surface temperature will accelerate the inorganic CO cycle, reducing its concentration to levels lethally low for plants (6995099999999999999 ♠ 10 ppm for C4 photosynthesis) in approximately 500--7002900000000000000 ♠ 900 Mys . The lack of vegetation will result in the loss of oxygen in the atmosphere, and animal life will become extinct . After another billion years all surface water will have disappeared and the mean global temperature will reach 7002343150000000000 ♠ 70 ° C (7002343150000000000 ♠ 158 ° F). From that point, the Earth is expected to be habitable for another 7016157788000000000 ♠ 500 Ma, possibly up to 7016725824800000000 ♠ 2.3 Ga if nitrogen is removed from the atmosphere . 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 . </P> <P> The Sun will evolve to become a red giant in about 7000500000000000000 ♠ 5 Bys . Models predict that the Sun will expand to roughly 1 AU (150 million km; 93 million mi), which is about 250 times its present radius . Earth's fate is less clear . As a red giant, the Sun will lose roughly 30% of its mass, so, without tidal effects, Earth will move to an orbit 1.7 AU (250 million km; 160 million mi) from the Sun when the star reaches its maximum radius . Most, if not all, remaining life will be destroyed by the Sun's increased luminosity (peaking at about 5,000 times its present level). A 2008 simulation indicates that Earth's orbit will eventually decay due to tidal effects and drag, causing it to enter the Sun's atmosphere and be vaporized . </P> <P> The shape of Earth is approximately oblate spheroidal . Due to rotation, the Earth is flattened along the geographic axis and bulging around the equator . The diameter of the Earth at the equator is 43 kilometres (27 mi) larger than the pole - to - pole diameter . Thus the point on the surface farthest from Earth's center of mass is the summit of the equatorial Chimborazo volcano in Ecuador . The average diameter of the reference spheroid is 12,742 kilometres (7,918 mi). Local topography deviates from this idealized spheroid, although on a global scale these deviations are small compared to Earth's radius: The maximum deviation of only 0.17% is at the Mariana Trench (10,911 metres (35,797 ft) below local sea level), whereas Mount Everest (8,848 metres (29,029 ft) above local sea level) represents a deviation of 0.14% . </P> <P> In geodesy, the exact shape that Earth's oceans would adopt in the absence of land and perturbations such as tides and winds is called the geoid . More precisely, the geoid is the surface of gravitational equipotential at mean sea level . </P>

What is the diameter of the earth in km