While it's true that life arose quickly on Earth (within the planet's first few hundred million years), the researchers point out that if it hadn't done so, there may not have been enough time for intelligent life — humans — to have evolved. So, in effect, we're biased. It took at least 3.5 billion years for intelligent life to evolve on Earth, and the only reason we're able to contemplate the likelihood of life today is that its evolution happened to get started early. This requisite good luck is independent of the actual probability of life emerging on a habitable planet.
On the other hand, if life arose simply by the accumulation of many specific chemical accidents in one place, it is easy to imagine that only one in, say, a trillion trillion habitable planets would ever host such a dream run. Set against a number that big — and once you decide a series of unlikely accidents is behind the creation of life, you get enormous odds very easily — it is irrelevant whether the Milky Way contains 40 billion habitable planets or just a handful. Forty billion makes hardly a dent in a trillion trillion.
Let's see what your statistics say after viewing this video.
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