Earth meeting probability with a large asteroid is rather small. Nevertheless it cannot be excluded completely, it is slightly higher than the probability of flight of an asteroid near our planet. In spite of the fact that there is no direct collision in this case, emergence of an asteroid near Earth all the same bears a number of threats.
During the existence Earth already faced asteroids, and it led every time to serious consequences for its inhabitants. On the surface of the planet more than one and a half hundred craters are revealed, diameter of some of them reaches 100 km.
The fact that falling of a large asteroid will lead to catastrophic destructions is well clear to any sane person. Not casually scientists of the leading countries of the world trace decades trajectories of flights of the most dangerous space bodies, develop options of counteraction to asteroid threat.
One of the most dangerous to people of Earth is the asteroid Apophis, according to forecasts it will approach Earth in 2029 on distance from 28 to 37 thousand kilometers. It is 10 times less, than distance to the Moon. And though scientists assure that the probability of collision is insignificant, so close pass of an asteroid can constitute serious danger to the planet. Apophis sizes are rather small, its diameter only 270 meters. But any asteroid is surrounded with the whole cloud of small particles, many of which can do harm to the spacecrafts put to orbit. At the speeds reaching several dozen kilometers per second even the mote is capable to cause serious damages. Apophis will pass where there are geostationary satellites, his small fragments threaten them most of all. Some part of substance of the asteroids which are flying by near Earth can get on its surface, it conceals the dangers too. Scientists assume that comets and asteroids can transfer microscopic organisms from some planets to others. Probability of it is small, but it is impossible to exclude it completely. In spite of the fact that the fragments of the heavenly wanderer which got to the atmosphere of the planet heat up to high temperature, some organisms can quite survive. And it, in turn, is very big threat for all live on Earth. Microorganisms alien to terrestrial flora and fauna can become deadly and at fast reproduction to lead of mankind to death. Similar scenarios look very improbable, however in practice they are quite possible. The terrestrial medicine still does not manage to cope even with the flu which is annually leading to death of hundreds of thousands of people. Now present the microorganism having ten times higher lethality, quickly breeding and capable it is easy to extend. Its emergence in the large city will become a real crash as it will be very difficult to hold the begun epidemic.