Scientists are fairly certain that life on earth can not survive more than five billion years from now. At that time, the sun will become unstable. Will expand into a red giant and swallow the Earth. However, all this will happen in the near future.
A large asteroid could theoretically hit Earth every time, and such a collision occurred at irregular intervals. In 2002, astronomers detected an asteroid the size of a football field. It passed close to Earth about a third of the way between the earth and the moon. What is surprising is that they only detected when really close to the earth. If steroids hit the earth, will have the same powers hydrogen bombs.