Self-sustaining chemical reactions that could support a biology radically different from life as we know it could exist on many different planets and use a variety of elements beyond the carbon on which life on Earth is based, research shows a new study.
On Soil, life is based on organic compounds. These molecules are composed of carbon and often also contain other elements such as hydrogen, oxygen, nitrogen, phosphorus and sulfur.
However, scientists have long wondered whether this is the case extraterrestrial life could evolve based on significantly different chemistry. For example, researchers have long speculated that silicon could also serve as a backbone for biology.
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“It’s important to explore these possibilities so that we have an idea of what all forms of life might look like, not just life on Earth,” said senior author Betül Kaçar, an astrobiologist, bacteriologist and evolutionary biologist at the University of Wisconsin- Madison. told Space.com.
One type of chemical interaction that is essential for life on Earth is known as autocatalysis. Autocatalytic reactions are self-sustaining: they can produce molecules that cause the same reaction to occur again. Imagine a growing population of rabbits. Pairs of rabbits come together, produce litters of new rabbits, and then the new rabbits grow up to form pairs and make even more rabbits. It doesn’t take many rabbits to quickly have many more rabbits.
“One of the main reasons origin of life researchers are concerned about autocatalysis is because reproduction – a key feature of life – is an example of autocatalysis,” Kaçar said. “Life catalyzes the formation of more life. One cell produces two cells, which can become four, and so on. As the number of cells multiplies, the number and diversity of possible interactions multiplies accordingly.”
In the new study, researchers looked for autocatalysis beyond organic compounds. They reasoned that autocatalysis could stimulate abiogenesis origin of life from lifelessness.
The scientists focused on so-called comproportionation cycles, which can generate multiple copies of a molecule. These products can be used as starting materials to allow these cycles to occur again, resulting in autocatalysis.
“Comproportionation is arguably unique in that it is a single reaction that produces multiples of an output — it is a lot like reproduction,” lead author Zhen Peng, an evolutionary biologist at the University of Wisconsin-Madison, told Space.com.
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To find these responses, the scientists analyzed more than two centuries of digitized scientific documents, written in many different languages. “With effective language search and translation tools, we were able to design and conduct this first-of-its-kind assessment of the ubiquity of autocatalytic cycles,” study co-author Zach Adam, a geologist at the University of Wisconsin-Madison. told Space.com.
Ultimately, the researchers discovered 270 different cycles of autocatalytic reactions. “Autocatalysis may not be so rare, but instead it could be a common feature of many different environments, even those that are truly different from Earth,” Kaçar said.
Most of the 270 cycles did not use organic compounds. Some focused on elements that are absent or extremely rare in life Soil, such as mercury, or the radioactive metal thorium. Some cycles are likely to occur only under extremely high or low temperatures or pressures.
The researchers even discovered four autocatalytic cycles involving noble gases, which only rarely if ever react chemically with other elements. If even a relatively inert gas like xenon could participate in autocatalysis, “there is good reason to think that autocatalysis occurs more readily in other elements,” Peng said.
Only eight of these cycles were relatively complex and consisted of four or more reactions. Most of the 270 cycles were simple, consisting of only two reactions each.
“These types of reactions were thought to be very rare,” Kaçar said in one rack. “We show that it is actually far from rare. You just have to look in the right place.”
The researchers noted that it is possible to combine multiple cycles, even if they are very different from each other. This could lead to self-sustaining chemical reactions that generate a wide range of molecules and cause a high degree of complexity.
“With so many basic recipes for autocatalysis available to draw from, the focus of research can now shift to understanding how autocatalysis, through comproportionation, can have more pronounced effects in shaping a planet’s chemistry,” said Kaçar.
The scientists hope that future research can experimentally test this new cookbook they created.
“The cycles presented here are a series of basic recipes that can be mixed and matched in ways never before attempted on our planet,” Peng said. “They could lead to the discovery of completely new examples of complex chemistry that operate in conditions where carbon- or even silicon-based cycles are overburned or frozen.”
It remains uncertain how plausible these cycles are, the researchers cautioned. “It is not guaranteed that all the samples we collected can be run in a laboratory or found on other astronomical objects,” Peng said.
In addition to the implications this work could have for the search for life in the universe and understanding the origins of life, this research could have practical applications, such as “optimizing chemical synthesis and making efficient use of resources and energy,” Adam said. “Another is the use of chemical compounds for interesting tasks such as chemical calculations.”
The scientists detailed their findings September 18 in the Journal of the American Chemical Society.
