Life on a distant planet, if it exists, may be nothing like life on Earth. But there are only a limited number of chemical ingredients in the universe’s pantry, and a limited number of ways to mix them. A team led by scientists at the University of Wisconsin-Madison exploited these limitations to write a cookbook containing hundreds of chemical recipes that could give rise to life.
Their list of ingredients could focus the search for life elsewhere in the universe by highlighting the most likely conditions (planetary versions of mixing techniques, oven temperatures, and cooking times) for recipes to be developed.
The process of progression from basic chemical ingredients to the complex cycles of cellular metabolism and reproduction that define life requires not only a simple beginning but also repetition, researchers say.
“The origin of life is actually a process from nothing,” says Betül Kaçar, a NASA-supported astrobiologist and professor of bacteriology at UW-Madison. “But it can’t happen just once. Life comes down to chemistry and the conditions that can generate a pattern of self-reproducing reactions.”
Chemical reactions that produce molecules that encourage the same reaction to happen again and again are called autocatalytic reactions. In a new study published in the Journal of the American Chemical SocietyZhen Peng, a postdoctoral researcher in the Kaçar laboratory, and his collaborators compiled 270 combinations of molecules, involving atoms from all groups and series of the periodic table, with the potential for sustained autocatalysis.
“We thought that this kind of reaction was very rare,” explains Kaçar. “We show that it’s actually far from rare. You just have to look in the right place.”
The researchers focused their research on what are called proportionality reactions. In these reactions, two compounds comprising the same element with a different number of electrons, or reactive states, combine to create a new compound in which the element is in the middle of the starting reactive states.
To be autocatalytic, the reaction result must also provide raw materials for the reaction to happen again, so the result becomes a new input, says study co-author and UW geoscientist Zach Adam. Madison studying the origins of life on Earth. Proportionality reactions result in multiple copies of some of the molecules involved, thus providing materials for the next steps of autocatalysis.
“If these conditions are met, you can start with relatively few of these results,” says Adam. “Every time you go around the cycle, you spit out at least one more output, which speeds up the reaction and makes it even faster.”
Autocatalysis is like a growing population of rabbits. Pairs of rabbits come together, produce litters of new rabbits, and then the new rabbits grow to pair up and form even more rabbits. It doesn’t take a lot of rabbits to soon have a lot more rabbits.
However, searching the universe for floppy ears and fuzzy tails is probably not a winning strategy. Instead, Kaçar hopes chemists will extract ideas from the new study’s list of recipes and test them in pots and pans simulating alien kitchens.
“We will never know for sure what exactly happened on this planet to generate life. We don’t have a time machine,” says Kaçar. “But, in a test tube, we can create multiple planetary conditions to understand how the dynamics necessary to sustain life might evolve in the first place.”
Kaçar leads a NASA-backed consortium called MUSE, for Metal Utilization & Selection Across Eons. Her lab will focus on reactions including the elements molybdenum and iron, and she’s excited to see what others cook up from the more exotic and unusual parts of the new cookbook.
“Carl Sagan said that if you want to make a pie out of nothing, you must first create the universe,” says Kaçar. “I think if we want to understand the universe, we need to bake some pies first.”
Zhen Peng et al, Evaluation of stoichiometric autocatalysis across element groups, Journal of the American Chemical Society (2023). DOI: 10.1021/jacs.3c07041
Provided by University of Wisconsin-Madison
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