How much longer can Earth support Life ???

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Life on earth will cease to exist long before the sun dies out in 5 billion years. In 1 million year, the sun will become hot enough to boil our oceans. For every billion years the sun spends burning hydrogen it gets about 10% brighter . Increased brightness mean an increase in the amount of heat our planet receives. As the planet heats up, the water on the surface of our planet will begin to evaporate. This will also change the location of the habitation zone around our star. The habitable zone is defined as the range of distances away from the star. Where water can be stable on the surface of a planet.

With a 10 % increase of brightness from our star the Earth will no longer be within habitable zone. This will make the beginning of the evaporation of our oceans. By the time the sun stops burning hydrogen, Mars will be in the habitable zone and the earth will be much too hot to maintain water on it's surface. This 10% increase in brightness will occur over the next billion year or so most models suggest that as the ocean evaporate more and more water will be present in the atmosphere instead of on the surface. 

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This will induce the greenhouse effect, trapping even more heat and causing more and more of the oceans to evaporate until the ground is mostly dry and the atmosphere holds the water at a high temperature. At the atmosphere gets saturated with water it will be bombarded by high energy light from the sun allowing the water to escape as hydrogen and oxygen. 

Eventually bleeding the earth dry of water and any hint of life. Some suggest that the earth will become inhospitable before the 1 billion year mark because of the interactions between the heating planet and the rocks, oceans and plate tectonic will dry out the planet even faster. Other suggest that life may be able to hold on a little  longer than 1 billion years due to the different requirements of life forms and periodic releases of critical chemicals by plate tectonics.

source: https://phys.org