Our sun is halfway through its life cycle. Its luminosity increases 1% every 110 million years. Therefore the Earth ineluctably grows hotter and hotter. In a billion years, life on its surface will be impossible. Global surface temperatures will reach 117F and the oceans will evaporate. Water molecules in the atmosphere will be broken apart by solar radiation and hydrogen molecules will escape the planet. Eventually the sun will exhaust the hydrogen fuel in its core. When it begins to exploit other material, its luminosity will increase a thousandfold until it stabilizes with a radius about 250 times its present size. It will consume Mercury and Venus but probably not the Earth which will become locked into an orbit with only one side facing the sun (as the moon does to the earth). This will mean impossibly hot temperatures on one side, impossibly cold on the other. The moon's orbit will reduce to 11,000 miles causing it to fracture, raining pieces of itself onto the Earth. Eventually the sun will lose mass and gravitational pull and the earth will drift away into a remote orbit -- dark, cold, and lifeless.
(Adapted from Douglas Palmer, Earth in 100 Groundbreaking Discoveries (Firefly Books, 2011.)