Scientists have looked through the cosmic pantry to write what has been described as a “cookbook” with hundreds of chemical “recipes” which have the potential to give rise to life.
Life, as far as we know, has only evolved once in the universe – on Earth.
But the specific chemical reactions that led to organisms on our home planet – with our DNA, fatty acids, and bills and taxes – may not be the same ones that form living things elsewhere in the universe.
The kinds of ingredients that could lead to life, however, are not limitless.
Above all, what is required, according to astrobiologists (scientists who study the possibility of life outside Earth) is repetitive chemical processes.
“The origin of life really is a something-from-nothing process,” says Betül Kaçar, a NASA-supported astrobiologist and University of Wisconsin–Madison professor of bacteriology. “But that something can’t happen just once. Life comes down to chemistry and conditions that can generate a self-reproducing pattern of reactions.”
Kaçar is the senior author of a paper published in the Journal of the American Chemical Society which compiles 270 combinations of molecules involving atoms from every group and series on the periodic table with the potential for sustained autocatalysis and, therefore, the evolution of life.
Autocatalytic reactions require that the output of the chemical reaction are also the new input, creating a sort of chemical feedback loop.
“It was thought that these sorts of reactions are very rare,” says Kaçar. “We are showing that it’s actually far from rare. You just need to look in the right place.”
The team hope their cookbook might help astronomers find the ingredients that are the chemical signs of life on other worlds.
Only last week, scientists reported in a preprint paper that the James Webb Space Telescope may have found signs of alien life on an ocean-covered world 50 light-years away. The exoplanet, K2-18b, is reported to have an atmosphere rich in hydrogen, methane, carbon dioxide and low levels of ammonia and dimethyl sulfide – known only to science as a biproduct of microbial life on Earth.
But until living organisms are definitively found elsewhere, the only life we know evolved here on Earth.
“We will never definitively know what exactly happened on this planet to generate life. We don’t have a time machine,” Kaçar says. “But, in a test tube, we can create multiple planetary conditions to understand how the dynamics to sustain life can evolve in the first place.”
Kaçar’s NASA-supported consortium called Metal Utilization & Selection Across Eons (MUSE) will focus on reactions including the elements molybdenum and iron.
“Carl Sagan said if you want to bake a pie from scratch, first you must create the universe,” Kaçar says. “I think if we want to understand the universe, first we must bake a few pies.”
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