The most common scenario is the death of the terrestrial biosphere is connected, of course, with the Sun. It was shining for about 5 billion years, every second emits a huge amount of energy. As a result of the collapse of the fusion of hydrogen nuclei per 1 cm2 comes 1.38 kWh of energy. This value is called the solar constant, is quite stable: it is very small fluctuations are associated with the magnitude of the solar "spots", ie. E. With the release of superheated mass of the solar energy in the photosphere (the so-called "prominences"). During the "glow" Sun has spent about half of its hydrogen reserves, which means that it is approximately in the middle of his career.
As you know, any star - a delicately balanced natural mechanism, and the Sun - our star. Through 7 to 8 billion years of it will remain a dead lump of nuclear waste, enclosed in an invisible "black dwarf." Final too sad, but to prevent this universal catastrophe not given to man. What incredible twists and turns do not seem to death of the Sun, the Earth (and, naturally, the biosphere), they are predicted not visionaries and scientists, whose authority in science is high enough.
Of course, there are other scenarios destruction of the biosphere. One of them is related to "visit" the earth comet. As you know, in space "wander" billions of comets, meteorites and asteroids. About every 300 years 50metrovye meteorites fall to Earth. Very dangerous asteroids near Earth where there are about 2000 But the most dangerous are the comet. They emerge from the depths of the solar system and anticipate all of a sudden encounter with them, at best, a few months. This time is too short to catch the comet forward towards diverting nuclear charge. Particularly difficult, experts say, to discover a comet coming from the sun.
Death of biosphere