The end of our Sun's current phase of development, after which it will swell into a red giant, either swallowing the Earth or at least completely scorching it. It is widely accepted by the scientific community that the earth will be destroyed around this time. However, as the Sun grows gradually hotter (over millions of years), the Earth may become too hot for life in only a billion years' time.
Carrington, D. (2000-02-21). "Date set for desert Earth". BBC News.