Earth, which has supported advanced life over an extended period of time, may be unique in the observable universe
A couple of months ago I discussed an upgrade to the Arecibo Radio Telescope that would make it more effective for searching for intelligent life in outer space (SETI). That article included references to cases made, from a secular and a theistic point of view, for the improbability of finding intelligent life “out there.” These approaches call attention to the vast number of conditions that must be met for life to survive in any environment and the difficulty in meeting those conditions all at the same time. The authors’ conclusion is that Earth, which has supported advanced life over an extended period of time, may be unique in the observable universe. This idea is often referred to as the Rare Earth Hypothesis.
Andrew Watson of the University of East Anglia in the UK reports, in the February 1, 2008 issue of Astrobiology, on a mathematical study he performed that lends further support for the idea that intelligent life in the universe is rare. While he approaches the problem from a naturalistic perspective, his arguments have broad application. He begins by noting that advanced life has appeared late in Earth’s history, approximately 4 billion years after primitive life first appeared. And due to the increase of the Sun’s luminosity, Earth can support this life another billion years at most—a short time compared with the time since its origin.
On the ground of some general principles entailed in the stochastic (statistical, involving random variables) model used for his study, Watson then argues that the timing of the appearance of intelligent life will be governed by the necessity of life passing at least four very difficult evolutionary steps. The four stages he chose correspond to major steps apparent in the fossil record, including the emergence of single-celled bacteria, complex cells, specialized cells allowing complex life-forms, and intelligent life with an established language.
Watson argues that each step is independent of the other and can only take place after the previous steps in the sequence have occurred. He estimates the probability of each step occurring as 10 percent or less, so the chance of intelligent life emerging in an Earth-like environment is low, less than 0.01 percent over the four billion years of life’s history. On this ground he concludes that even with Earth-like conditions, there is still a very low probability that intelligent life will develop.
If we multiply this percentage by the extremely small probability for finding an Earth-like environment, then the likelihood for finding intelligent life anywhere else in the observable universe is virtually zero. This study argues against a random chance scenario, but fits well with the RTB creation model, where we expect that the appearance of life requires the direct hand of a creator who has placed it in this universe for a purpose.