"Long before it's in the papers"
January 22, 2016

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The aliens are silent because they died out, study says

Jan. 22, 2016
Courtesy of Aus­tral­ian Na­t­ional Un­ivers­ity
and World Science staff

Life on oth­er plan­ets would likely be brief and go ex­tinct quick­ly, say sci­en­tists at Aus­tral­ian Na­t­ional Un­ivers­ity in a new stu­dy.

In re­search aim­ing to un­der­stand how life might de­vel­op, they con­clud­ed that new life would com­monly die out due to run­away heat­ing or cool­ing on their fledg­ling plan­ets.

“The uni­verse is probably filled with hab­it­a­ble plan­ets, so many sci­en­tists think it should be teem­ing with aliens,” said Ad­it­ya Cho­pra, lead au­thor of a pa­per on the re­search, pub­lished in the jour­nal As­tro­bi­ol­o­gy.

“Early life is frag­ile, so we be­lieve it rarely evolves quickly enough to sur­vive.”

“Most early plan­e­tary en­vi­ron­ments are un­sta­ble. To pro­duce a hab­it­a­ble plan­et, life forms need to reg­u­late green­house gas­es such as wa­ter and car­bon di­ox­ide to keep sur­face tem­per­a­tures sta­ble.”

About four bil­lion years ago Earth, Ve­nus and Mars may have all been hab­it­a­ble, he not­ed. But a bil­lion years or so af­ter forma­t­ion, Ve­nus turned in­to a hot­house and Mars froze in­to an ice­box. Early mi­cro­bi­al life on those two worlds, if any, failed to sta­bi­lize the rap­idly chang­ing en­vi­ron­ment, said co-au­thor Char­ley Line­weav­er. “Life on Earth probably played a lead­ing role in sta­bi­liz­ing the plan­et’s cli­mate,” he added.

Chopra said the the­o­ry solves a puz­zle.

“The mys­tery of why we haven’t yet found signs of aliens may have less to do with the like­li­hood of the or­i­gin of life or in­tel­li­gence and have more to do with the rar­ity of the rap­id emer­gence of bi­o­log­i­cal regula­t­ion of feed­back cy­cles on plan­e­tary sur­faces,” he said.

Wet, rocky plan­ets, with the in­gre­di­ents and en­er­gy sources re­quired for life seem to be com­mon through­out the cos­mos. But as phys­i­cist En­ri­co Fer­mi point­ed out in 1950, no signs of sur­viv­ing extra-terrestrial life have been found.

A plau­si­ble so­lu­tion to Fer­mi’s par­a­dox, say the re­search­ers, is near uni­ver­sal early ex­tinction, which they have named the Ga­ian Bot­tle­neck.

“One in­tri­guing pre­dic­tion of the Ga­ian Bot­tle­neck mod­el is that the vast ma­jor­ity of fos­sils in the uni­verse will be from ex­tinct mi­cro­bi­al life, not from mul­ti­-cellular spe­cies such as di­no­saurs or hu­manoids that take bil­lions of years to evolve,” said Line­weaver.


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Life on other planets would likely be brief and become extinct very quickly, say scientists at Australian National University in a new study. In research aiming to understand how life might develop, the investigators concluded that new life would commonly die out due to runaway heating or cooling on their fledgling planets. “The universe is probably filled with habitable planets, so many scientists think it should be teeming with aliens,” said Aditya Chopra, lead author of a paper on the research, published in the journal Astrobiology. “Early life is fragile, so we believe it rarely evolves quickly enough to survive.” “Most early planetary environments are unstable. To produce a habitable planet, life forms need to regulate greenhouse gases such as water and carbon dioxide to keep surface temperatures stable.” About four billion years ago Earth, Venus and Mars may have all been habitable, he noted. But a billion years or so after formation, Venus turned into a hothouse and Mars froze into an icebox. Early microbial life on Venus and Mars, if there was any, failed to stabilize the rapidly changing environment, said co-author Charley Lineweaver. “Life on Earth probably played a leading role in stabilizing the planet’s climate,” he said. Chopra said the theory solves a puzzle. “The mystery of why we haven’t yet found signs of aliens may have less to do with the likelihood of the origin of life or intelligence and have more to do with the rarity of the rapid emergence of biological regulation of feedback cycles on planetary surfaces,” he said. Wet, rocky planets, with the ingredients and energy sources required for life seem to be ubiquitous. But as physicist Enrico Fermi pointed out in 1950, no signs of surviving extra-terrestrial life have been found. A plausible solution to Fermi’s paradox, say the researchers, is near universal early extinction, which they have named the Gaian Bottleneck. “One intriguing prediction of the Gaian Bottleneck model is that the vast majority of fossils in the universe will be from extinct microbial life, not from multi-cellular species such as dinosaurs or humanoids that take billions of years to evolve,” said Associate Professor Lineweaver.