The big bang theory and the other theory about life coming from outer space and dropping onto earth, are merely attempts to dodge around the questions of how matter was formed originally and how life started from inert matter.
In the 1970s a British astronomer, Fir Frederick Hoyle, calculated the probability of spontaneous generation of a single bacterium. He determined that the probability of generating the proteins necessary to form a single amoeba was one chance in 10 40,000 . To put this in perspective, if an event has the probability of one chance in 10 50 it is considered a mathematical impossibility.
"The likelihood of the formation of life from inanimate matter is one to a number with forty thousand naughts [zeros] after it. It is enough to bury Darwin and the whole theory of evolution. There was no primeval soup, neither on this planet nor on any other, and if the beginnings of life were not random they must therefor have been the product of purposeful intelligence."
-Sir Frederick Hoyle.