Australian scientists say they've figured out why we've been unable to detect signs of alien life. And for those who dream of someday meeting up with a real-life E.T., it's a pretty depressing reason.
In a paper published this week in the journal Astrobiology, the researchers hypothesize that alien life forms may well have arisen many times in many different places, but were quickly snuffed out when extreme heating or cooling rendered their host planets uninhabitable.
"Early life is fragile, so we believe it rarely evolves quickly enough to survive," Aditya Chopra, an astrobiologist at Australian National University in Canberra and lead author of the paper, said in a written statement. In other words, it succumbs to temperature extremes long before it has a chance to evolve beyond the microbe level.
Not everyone is convinced.
"Early Armageddon, as proposed here, may occur on some planets some of the time," Seth Shostak, senior astronomer at the SETI Institute in Mountain View, California, told The Huffington Post in an email. "However, while change may thin the cosmic herd, I can hardly imagine it inevitably wipes the herd out."
Shostak pointed to Earth as an obvious example of how life can evolve and persist for billions of years. "Consider that in 65 million years, mammals went from being small rodents to becoming us," Shostak said. "In other words, even if the neighborhood deteriorates, life has time enough to adapt."
But the fates of Earth's own planetary neighbors seem consistent with the hypothesis. As Chopra explained in an email to The Huffington Post:
Even though Venus, Earth and Mars are thought to have been essentially identical about 4 billion years ago, Mars and Venus experienced runaway conditions. Earth did not experience the same fate -- plausibly because the interaction between Earth-life and its environment was such that a planetary-wide biological regulation of greenhouse gases was able to provide a negative feedback to counter the positive geochemical or atmospheric feedback cycles.
Charles Lineweaver, associate professor of astronomy at Australian National University and co-author of the paper, told HuffPost Science in an email that life on Earth is "a rare exception to the cosmic default, which is early extinction."
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