How many the mankind needed to live?As long still will exist our civilization? You think that there are no limits? Well - well. Dinosaurs too so once thought... If to take to the maximum, then physicists claim that our Sun will shine 4 - 5 billion more years, and then will go out and will die. And together with it, naturally, also all life on Earth will die. Approximately in 45 days after the Sun goes out.
A geologists tell that and it is not necessary to wait for billions of years - according to them for passed couple of honeycombs millions of years Earth shook such global cataclysms that practically all fauna existing at that time on Earth and flora turned century. minerals and later how many - that thousands (tens of thousands) of years Earth descendants of those who managed to endure the next cataclysm began to occupy. Evolution was started over again, having forgotten about an unsuccessful stage.
What we are threatened by cataclysms? Yes different, very different. As regards the reasons of cataclysms scientists - predictors of an apocalypse are very inventive.
the Supernew star
Is options exotic: near us (within several tens light years) supernew is formed - and the stream of rigid radiation kills all live on the planet, there are only those who are covered from rigid radiation with thickness of the earth (i.e. lived in caves), and those who were covered by the thick sheet of water which absorbed radiation i.e. deep-water fishes and other living inhabitants of big depths.
Well, a supernew star in near vicinities of Earth or the wandering planet which is flying by through Solar system it is obligatory near Earth - it is, most likely, dashing inventions of fantasts. On the frequency of emergence supernew just in a visibility range from Earth, formation of this phenomenon absolutely is close to Earth almost incredibly. Rather the Sun will fuse and will go out. Unfortunately, there are things much more probable and, moreover, the developments of Earth which were already happening in the history.
On Solar system rush asteroids. Once, long ago, when our system was only created, all its space was filled with the pieces of substance flying, crashing each other. Dust from the dust cloud which became a basis of Solar system stuck together under the influence of gravitation in pieces, those stuck together in pieces... Well and so on. As a result the most part of the former dust was grouped in the Sun and planets. But some part of substance and remained... As if restless. At the same time their most part turns in a cometary Oort cloud, on the very brink of our system.
But, facing with each other, they sometimes change orbits and the Sun which are carried away by an attraction fly to the center of system. A way this far and dangerous - for those who will occur it in the path. The largest asteroids, their orbits, speed, are known to terrestrial astronomers. On our happiness, among them there is only one asteroid, Apofis who has some probability to face Earth in 2036. In 2029 when it flies by by us once again, we learn in more detail about our prospects to live or die in accident. But so far scientists consider that collision with it is extremely improbable.
Our happiness is that Earth - such small, it is very difficult to get to it. However... Large meteorites and even which - fall from time to time to our Ground that it is more. And already on our memory over Chelyabinsk jerked a meteorite. Our happiness that it entered the atmosphere at an acute angle and therefore blew up very highly: to the Earth`s surface there were about 25 more kilometers and to the next large city, Chelyabinsk, the distance was decent. Explosion its force, by different estimates, made from 100 to 400 kilotons of trotyl. Present what would be if it reached a surface? It is possible to be sure that in this case the number of the victims would not be limited to one and a half thousand victims.
For memories of our civilization there was still a falling of the Tungus meteorite. And again happiness - it fell in almost deserted taiga, for hundreds and thousands of kilometers from the cities. And be its speed slightly - slightly more or less and fall it to some ocean?. And get it to Western Europe?. Presented? Were terrified?
during a volcanic eruption of Saint Elena (the USA, the State of Washington) in May, 1980 died 57 people.
During a volcanic eruption of Krakatau in 1883 about 36000 people died (nobody considered the most part of the died natives - who knows them how many they were on those islands when the tsunami came?) . By calculations of volcanists, occur similar eruption presently - the victims would be estimated in millions, despite the system of a prediction of a tsunami existing now...
And on the place of explosion of Krakatau Anak - Krakatau (the son of Krakatau) already grew up, the mountain of a volcanic origin which reached height of hundreds meters and continues to grow... What will be when also the son of Krakatau (God forbid) explodes? Once deserted coasts - the blossoming resorts, all coast are built up and populated for a long time long ago. What will be when...?
And generally, for the ordinary person all these terms have purely speculative value. When not in 2000 - m, not in 2001 the reporter interrogated passersby about their plans for the new millennium, one quite reasonably noticed that he is absolutely sure that it should not build plans for the millennium - it the most part of the new millennium will be dead...
So if the cataclysm happens not tomorrow, it is not interesting to much any more. However the Chelyabinsk meteorite was noticed, only when it entered the atmosphere and blew up. 400 kilotons of explosive, invisible to terrestrial observers, which at any time can fall anywhere.