Max Robinson, Ph.D. Molecular Biology and Biotechnology & Evolutionary Genetics, University of Washington (2005)
Answered March 15, 2018
The thing about abiogenesis happening by chance is that one needs to take into account two very important details:
1. In order to pose the question, life has to exist, and more than that, it has to exist where the question is being asked. Wherever we were in the Universe is where we would ask, so we have to consider how likely life was to arise anywhere in the Universe, our interest in life on this particular planet just comes from us already being here.
The size of the laboratory. Suppose you play a game with one chance in ten of winning; 90% of the time, you will lose. But suppose that you and 9 friends each play that game on the same day. What is the probability that all 10 of you will lose? It is .910=.3492. so it is more likely that at least one of you will win. Suppose you had 99 friends play, instead of just 9; then how likely is it none of you will win? That is 0.9100=0.0000266, or one chance in 37,649. So it isn't really a matter of how unlikely it is to win, as much as it is how that chance compares to how many times you try.
Now, how many planets are there in the universe? Only counting the ones that have conditions, like liquid water, that could support life. Oh we had better double it, because based on our own solar system, there are planet-sized moons that have liquid water, too. There must be millions in our galaxy, and there are billions of galaxies. Now take the size of a laboratory: how many laboratories would fit in Earth's oceans? Again, billions. So we have about a billion billion million laboratories in the universe where abiogenesis might happen any day. And how many days has the average laboratory been around? Well, the ones on Earth have existed for about 4 billion years, and each year is 365 days, so let's round it to a trillion.
So there you have it. The universe has had about a million billion billion trillion laboratory days in which to have abiogenesis occur by dumb luck; all that we need to show is that abiogenesis has at least, say, one chane in a billion billion trillion of happening in a laboratory day, and there should be about a million places in the universe where it has happened by now. As far as I am concerned, the ease with which the conditions on early Earth, replicated in a laboratory, rapidly produce the same organic molecules that are the basis of life on Earth, in just one laboratory in a very small number of tries, suggests that the chance of abiogenesis is much, much greater than one in a billion billion trillion.
And since we know there is someone on this particular planet who has reached sentience as has asked the question, it seems pretty likely that at least one of the laboratories that succeeded was here on Earth.
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