“The universe is probably filled with habitable planets, so many scientists think it should be teeming with aliens,” said Dr Aditya Chopra from the ANU Research School of Earth Sciences and lead author on the paper, which is published in 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.” It’s possible that Earth, Venus and Mars may have all been habitable four billion years ago, reports Dr Phil Dooley for ANU. However, Venus quickly became a hothouse and Mars a frozen icebox. According to co-author Associate Professor Charley Lineweaver from the ANU Planetary Science Institute, there may have been early microbial life on these planets, but it most likely would have failed to stabilize in an environment that is rapidly changing. “Life on Earth probably played a leading role in stabilising the planet’s climate,” he said. “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,” Dr. Chopra said. While wet, rocky planets, with the ingredients and energy sources conducive to life may seem to be common; however, no signs of living extraterrestrial life have been found in 1950, pointed out physicist Enrico Fermi. The researchers say that a believable solution to Fermi’s paradox is near early extinction worldwide, 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 multicellular species such as dinosaurs or humanoids that take billions of years to evolve,” said Associate Professor Lineweaver. A copy of the paper can be downloaded here.
