Creationists sometimes try and use statistics and numbers to bamboozle people into thinking that evolution is too unlikely to happen, well two can play at that game.
A real scientist (as opposed to a creationist) has run the numbers on it. The odds that all life evolved from more than one ancestor (i.e. that not everything on earth is related), are one in ten to the power of 2680. That's a 1 with 2680 0's after it. You may notice that we're taking the assumption that life evolves, and has evolved to where it is right now. This is because evolution is an established scientific fact.
So, we conclude that the odds are astronomically in favour of all life evolving from a single common ancestor (3.5 billion years ago).
If you'd like to read more, visit This Page on National Geographic.