As the sun ages, what will happen to life here on earth? why?

Our Sun will slowly get hotter as more and more Helium accumulates in the Sun's core. In ~1 billion years, liquid water will no longer be possible on Earth's surface, and the oceans will completely boil away, resulting in a Venus-like planet. Only thermophyllic bacteria may be able to survive, perhaps at the poles. In ~4-5billion years, our Sun will have converted ~10% of its Hydrogen to Helium, and thus become so hot that Helium to Carbon fusion will begin in earnest, causing the "Helium flash" which will convert our Sun into a red giant, and swallow and vaporize all of the rocky inner planets. It may even blow off a planetary nebula. (Contrary to what the others have said, our Sun will not 'run out' of Hydrogen.) 

Yeah, you can cry underwater but you just can't see the tears since you're already in water. just because you're crying doesn't mean you have to feel the wetness of your tears. s ya