Extraterrestrial life may flash out of existence as quickly as it flashes into existence, according to astrobiologists from ANU Research School of Earth Sciences.
In an effort to understand how life might have originated, the researchers hypothesize that life quickly dies out as soon as it develops due to the runaway heating or cooling of planets.
This could provide a resolution to the infamous Fermi Paradox, which state the universe should be crawling with extraterrestrial civilizations and yet, they are nowhere to be found.
“The universe is probably filled with habitable planets, so many scientists think it should be teeming with aliens,” Dr. Aditya Chopra, lead author of the study, said in a statement.
“Early life is fragile, so we believe it rarely evolves quickly enough to survive,” she added. “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.”
A fleeting window of opportunity
The authors of the study, published in the journal Astrobiology, suggest that since burgeoning planets are unstable, there is a fleeting window of opportunity for life to evolve. Once that window shuts, it’s game over.
Planets are hot and heavily bombarded with debris during their first 500 million years of existence – conditions that are not hospitable to life. Life can develop over the next 500 million years, as it did on Earth, as the planets cool.
Unfortunately, during that time, planets often loose their liquid water, either by freezing over or as a consequence of the greenhouse effect. This can convert a hospitable environment into an inhospitable environment, as was the case with Mars and Venus.
If microbial life did once exist on Venus and Mars, then it failed to stabilize the planets’ environment, according to co-author of the study, Associate Professor Charley Lineweaver from the ANU Planetary Science Institute. “Life on Earth probably played a leading role in stabilising the planet’s climate,” he said.
The Gaian bottleneck hypothesis
“Between the early heat pulses, freezing, volatile content variation, and runaway positive feedbacks, maintaining life on an initially wet rocky planet in the habitable zone may be like trying to ride a wild bull. Most life falls off,” write the authors of the study. “Life may be rare in the universe, not because it is difficult to get started, but because habitable environments are difficult to maintain during the first billion years.”
The team describes this proposal as the “Gaian Bottleneck” hypothesis. This is in contrast to the “emergence bottleneck” hypothesis, which states it’s difficult for life to develop in the first place. If the origin of life was an astronomically unlikely event, as the emergence bottleneck hypothesis suggests, then scientists would be the awkward position of looking for a hypothesis that is intrinsically improbable.
Dr. Chopra believes their hypothesis best resolves the Fermi Paradox. “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.
Each hypothesis has its contenders. However, the researchers note that the Gaian bottleneck hypothesis can at least be tested. “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 multicellular species such as dinosaurs or humanoids that take billions of years to evolve,” Lineweaver said in the same statement.