KentuckyFC writes "As the Sun expands into a red giant, life on Earth will die away. Now astrobiologists have worked out how this will look to distant observers watching the biosignature in our atmosphere. They say the first major effect of warming, about 1 billion years from now, will be a dramatic drop in atmospheric carbon dioxide as the oceans absorb more of it. That's bad news for trees and plants, which need carbon dioxide for photosynthesis, so they begin to die off. Since plants produce oxygen, atmospheric levels of oxygen will also drop, killing off the animals. Roughly 2 billion years from now, the only living things on Earth will be microbes. However, methane levels will have risen dramatically, caused by decaying plant matter. And decaying animals will release a gas called methanethiol, which breaks down into ethane, which ought to be visible too. Finally, they calculate that about 3 billion years from now, the oceans will boil and Earth will be a barren planet with little if any biosignature at all. But all this is not just a subject of morbid fascination. With the next generation of space telescopes, astronomers should see similar biosignatures on Earth-like planets around other stars that are also beyond their sell-by dates. So we'll be able to watch them die off first."