ACTON, Australia, Jan. 22 (UPI) -- Researchers in Australia say climate change is the reason why we haven't meet any aliens yet. And it's the reason why we may never meet any.
The scientists at the Australian National University aren't talking about climate change here on Earth, but elsewhere in the universe.
There are seemingly thousands of potentially habitable planets out there in the cosmos. The numbers say there should be alien life out there. But astronomers say climatic conditions may simply be too unstable, never allowing enough time for life to evolve.
There may have been -- or may be -- alien life out there, but it likely didn't -- or won't -- last long.
"Early life is fragile, so we believe it rarely evolves quickly enough to survive," Aditya Chopra, a professor at the ANU Research School of Earth Sciences, said in a press release.
"Most early planetary environments are unstable," Chopra added. "To produce a habitable planet, life forms need to regulate greenhouse gases such as water and carbon dioxide to keep surface temperatures stable."
Chopra is the lead author of a new paper on the unlikeliness of alien life, published this week in the journal Astrobiology.
In modeling the likelihood of the evolution of early life on faraway planets, researchers say they may have helped solve Fermi's paradox.
Several billion years ago, Earth, Venus and Mars were all relatively habitable. But only Earth managed to sprout life forms. Venus quickly became too hot and Mars too cold. So why Earth?
Earth's secret may not simply be habitability, but life itself. As early life forms emerged and evolved, they shaped the planet in novel ways that stabilized the climate and encouraged the development of newer and more complex life forms.
"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," Copra explained.
Universal early extinction explains why so many wet, rocky planets are without life. Copra and his colleagues dubbed the solution to the paradox 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 multicellular species such as dinosaurs or humanoids that take billions of years to evolve," said co-author Charley Lineweaver, a professors at the ANU Planetary Science Institute.