In research aiming to understand how life might develop, scientists realized 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 from ANU.
“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. However, a billion years or so after formation, Venus turned into a hothouse and Mars froze into an icebox.
The Case for a Gaian Bottleneck: The Biology of Habitability
Nextbigfuture notes that
the fact that Mars or Venus might not have life that our solar system has at least ten planets, moons and dwarf planets with liquid oceans. They likely have at least microbial life. We also just found a new planet in the solar system that is about 4 to ten times bigger than earth.
Planet Nine, it "has a mass about 10 times that of Earth and orbits about 20 times farther from the sun" than Neptune. That means "it would take this new planet between 10,000 and 20,000 years to make just one full orbit around the sun," according to Caltech.
Researchers Konstantin Batygin and Mike Brown haven't actually seen the planet, but other research helped lead them to conclude that there is one. Basically, they found that certain objects in the Kuiper Belt -- the field of icy objects and debris beyond Neptune -- had orbits that peculiarly pointed in the same direction.
Early microbial life on Venus and Mars, if there was any, failed to stabilize the rapidly changing environment, said Charley Lineweaver from ANU.
“Life on Earth probably played a leading role in stabilizing the planet’s climate,” he said.
Chopra said their theory solved 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, however, as 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 multicellular species such as dinosaurs or humanoids that take billions of years to evolve,” said Lineweaver
In planetary astronomy and astrobiology, the Rare Earth Hypothesis argues that the origin of life and the evolution of biological complexity such as sexually reproducing, multicellular organisms on Earth (and, subsequently, human intelligence) required an improbable combination of astrophysical and geological events and circumstances. The hypothesis argues that complex extraterrestrial life is a very improbable phenomenon and likely to be extremely rare. The term "Rare Earth" originates from Rare Earth: Why Complex Life Is Uncommon in the Universe (2000), a book by Peter Ward, a geologist and paleontologist, and Donald E. Brownlee, an astronomer and astrobiologist, both faculty members at the University of Washington.
An alternative view point was argued by Carl Sagan and Frank Drake, among others. It holds that Earth is a typical rocky planet in a typical planetary system, located in a non-exceptional region of a common barred-spiral galaxy. Given the principle of mediocrity (in the same vein as the Copernican principle), it is probable that the universe teems with complex life. Ward and Brownlee argue to the contrary: that planets, planetary systems, and galactic regions that are as friendly to complex life as are the Earth, the Solar System, and our region of the Milky Way are very rare.
Abstract - The Case for a Gaian Bottleneck: The Biology of Habitability
The prerequisites and ingredients for life seem to be abundantly available in the Universe. However, the Universe does not seem to be teeming with life. The most common explanation for this is a low probability for the emergence of life (an emergence bottleneck), notionally due to the intricacies of the molecular recipe. Here, we present an alternative Gaian bottleneck explanation: If life emerges on a planet, it only rarely evolves quickly enough to regulate greenhouse gases and albedo, thereby maintaining surface temperatures compatible with liquid water and habitability. Such a Gaian bottleneck suggests that (i) extinction is the cosmic default for most life that has ever emerged on the surfaces of wet rocky planets in the Universe and (ii) rocky planets need to be inhabited to remain habitable. In the Gaian bottleneck model, the maintenance of planetary habitability is a property more associated with an unusually rapid evolution of biological regulation of surface volatiles than with the luminosity and distance to the host star.