Is Intelligent Life As Uncommon As Rare Earth First Proposed?
File Photo: The Crew Of Apollo 17 Took This Photograph Of Earth In December 1972 While The ... [+] Spacecraft Was Traveling Between The Earth And The Moon. The Orange-Red Deserts Of Africa And Saudi Arabia Stand In Stark Contrast To The Deep Blue Of The Oceans And The White Of Both Clouds And Snow-Covered Antarctica. (Photo By Nasa/Getty Images) Getty Images  Twenty years ago, two University of Washington professors, a respected paleontologist and a well-known astronomer, co-authored a book that turned the planetary science community on its head. With the publication of Rare Earth: Why Complex Life is Uncommon in the Universe, Peter Ward and Donald Brownlee explained why microbial life may be ubiquitous in the universe, but intelligent life may be rare indeed. They are now working on a sequel, tentatively titled The Rare Earth Hypothesis: Assessing the Frequency of Complex Life in the Cosmos, in the Age of Exoplanet Discovery.  Its been a productive two decades for exoplanet hunters, astrobiologists, and SETI searchers. But the goalposts appear to be shifting. Like a desert mirage, the task of assessing the rarity of intelligent life in the universe seems to become more convoluted with each passing year. Our best new view of the origin of life is that where it first came together was not at all where most, or perhaps even any of its component parts were constructed, the authors write in their new books proposal. For life to evolve from non-life, there needed to be an energetic world of enormous geological diversity.  That means that even the ratio of ocean to land on a potentially habitable world is perhaps a key in not only getting life, but also keeping it, the authors write. Dont forget that everything we know about life in the universe stems from our own experience here with the life we study here on planet Earth. Putative extrasolar earths and speculation about microbial fossils on Mars, or even extant life deep within the oceans of one of our solar systems far-flung frozen moons, remains speculation at this point. Yet Earth was blessed with an anomalously large moon created from a random catastrophic impact with our nascent planet. Our large moon created ocean tides that four billion years ago, were an order of magnitude larger in amplitude than those today, the authors write. If the onset of microbial life here was dependent on daily tides of great amplitude, carrying organic molecules into geographic tidal basins where they were repeatedly dehydrated and then rehydrated, even extrasolar microbial life could be rare, they note. As our result, our own Moon may have been responsible for the tides that led to the concentration and chemical changes needed to spark the onset of complicated organics and the precursors of nucleic acids. Arriving at our current configuration of planets, with their very different sizes and places outward from the Sun, was itself a rarity, write the authors. Exoplanet discoveries have revealed that most systems have Jupiter-style [that] planets spiral in and earthlike planets are destroyed by their star. Our solar system is a very rare exception.  The authors note that rocky planets in orbit around Red Dwarf stars, the most ubiquitous out there would be plagued by very strong solar flares and solar winds. The flares would blast nearby planets with lethal radiation, and the winds would tend to strip atmospheres, like Mars in our system, the authors note. This is likely because a habitable planet would be tidally locked and not rotate, and therefore could not have an earth-style magnetic field to shield the atmosphere from radiation, they note. Even so, there is an awful lot of astrobiological overselling, Peter Ward, co-author of Rare Earth and a paleontologist at the University of Washington in Seattle, told me. A week does not go by without some new exoplanet being plugged as the new second earth, he says. Ultimately, this sort of oversell creates a cynical public. People hear time and again that life is ubiquitous and yet SETI comes up empty year after year and we remain decades away from finding microfossils on Mars. I even see the strange new concept of super habitable planets, said Ward. Seems like selling used cars - try out this three times earth sized planet! Perfect for flatworms! Giraffes need not apply for emigration!  The crux of the Rare Earth Hypothesis seems to be that intelligent life on Earth is rare because we are the end result of a lot of serendipitous Goldilocks-type events. I would bet my life in an instant that there are other intelligent species in our galaxy, said Ward. The numbers are too great to believe otherwise.  But Ward cautions that the fossil record is humbling because of what it tells us about extinction. Living fossils - living examples of an otherwise extinct group that have remained virtually unchanged over the eons - are the exception, not the rule, he says. But before the long road to intelligence can even begin its journey down the yellow-brick road of complex life, it first needs a planet that can maintain liquid water and stable temperatures over billions of years of geologic time. Thats no small feat. For a species to evolve into anything approaching Human or even Cetacean intelligence requires the kind of evolutionary serendipity that continues to amaze us all.