“Any extraterrestrial organisms we find will be made of the same atoms we are,” observes Harvard’s Center for Astrophysics, Avi Loeb, about the recent detection of a potential biosignature in the atmosphere of Venus, the nearest planet to Earth where NASA is currently considering sending a spacecraft.
“Microbes may reside there” in the Venusian cloud deck 35 miles above ground level, where the temperature and pressure are similar to what they are in the lower atmosphere of Earth,” writes Loeb in Scientific American, “in droplets at a density that is orders of magnitude smaller than in air on Earth; if so, they could have common ancestry to terrestrial life, given that asteroids occasionally graze the atmospheres of both planets, potentially transferring material from one to the other.”
This week, though, three independent studies announced that they have failed to find evidence of phosphine in the Venusian atmosphere, casting doubt on whether the gas could be produced by alien microbes.
Venus –The Solar System’s First Habitable Planet
Yet recent research by Yale astronomers suggests that our Moon may harbor clues that Venus –described by Stephen Hawking as Earth’s “kissing cousin– may have had an Earth-like environment billions of years ago, with water and a thin atmosphere. Their findings follow research suggesting that our sister planet may have been the solar system’s first habitable planet.
The possibility of current or past life on Venus raises a hotly debated question of how closely extraterrestrial life would evolve to resemble that on Earth, with some scientists, such as Harvard’s evolutionary theorist, Stephen Jay Gould, who argued that with a slightly different roll of the Darwinian dice, earth would have been inhabited by creatures unimaginable, while others such as Charles S. Cockell, an astrobiologist at the University of Edinburgh and Director of the UK Center for Astrobiology, conjecture that if there is biology elsewhere in the universe we would find it strikingly familiar down to the carbon-based machinery in its cells. All life is simply living matter, “material capable of reproducing and evolving.”
Physics of Life
In his book, The Equations of Life: How Physics Shapes Evolution, Cockell conjectures that the cosmos if populated, would harbor creatures more like like those lined up at Mos Eisley’s dimly-lit cantina on the Star Wars planet Tatooine. No matter how different the conditions on distant worlds, suggests Cockell, “all life being living matter –material capable of reproducing and evolving–is presumably subject to the same laws of physics — from quantum mechanics to thermodynamics and the laws of gravity.”
Early Earth was covered with carbonaceous material from meteorites and comets that provided the raw materials from which first life emerged. In his book, The Eerie Silence, astrophysicist Paul Davies echoes Harvard’s Gould suggesting that the original cells would have been able to pick and choose from the early Earth’s organic cocktail. To the best of our knowledge, he writes, “the twenty-one chosen by known life do not constitute a unique set; other choices could have been made, and maybe were made if life started elsewhere many times.”
Biology’s Great Mystery
Cockell writes George Johnson for the New York Times, “lucidly addresses biology’s great mystery: If we grant that life is an interplay of chance and necessity, in the words of the French biochemist Jacques Monod, then which has the upper hand?” In a nod to Monod, Cockel “argues that even at this deep level, the possibilities of life were tightly circumscribed. Rerun the tape of evolution, and DNA, RNA, ATP, the Krebs cycle — the rigmarole of Biology 101 — would probably arise again, here or in distant worlds. Single cells would then join together, seeking the advantages of metazoan life, until before you know it something like the earthly menagerie would come to be.”
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