Life on a distant planet, if it exists, may be very different from life on Earth. But there are so many chemical ingredients in the pantry of the universe, and so many ways to mix them. Using these limitations, a team led by scientists at the University of Wisconsin-Madison has written a cookbook with hundreds of chemical recipes that could potentially give birth to life.

Ingredient lists can point out the most likely conditions for recipes to come together—planetary versions of mixing techniques, oven temperatures, and cooking times—that can focus on the search for life elsewhere in the universe. The process of progressing from basic chemical components 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 of something from nothing,” says Betul Kachar, a NASA-supported astrobiologist and professor of bacteriology at the University of Madison. “But it can’t happen once. Life boils down to chemistry and conditions that can create a self-replicating reaction pattern.”

Chemical reactions that produce molecules that cause the same reaction to be repeated over and over are called autocatalytic reactions. In a new study published Journal of the American Chemical SocietyZhen Peng, a postdoctoral researcher in the Kaçar lab, and his colleagues assembled 270 combinations of molecules with sustained autocatalysis potential, containing atoms from all groups and series in the periodic table.

“Such reactions were believed to be very rare,” says Kachar. “We show that, in fact, it is far from rare. You just have to look in the right place.”

The researchers focused their research on so-called proportioning reactions. In these reactions, two compounds containing the same element with different numbers of electrons or reactive states combine to form a new compound in which the element is in the middle of the original reactive states.

To be autocatalytic, the output of the reaction must also provide the starting materials for the reaction to repeat itself, so that the output becomes a new input, says study co-author Zach Adam, a UW–Madison geologist who studies the origins of life on Earth. Ratio reactions lead to the appearance of multiple copies of some of the molecules of interest, providing material for subsequent stages of autocatalysis.

“If these conditions are right, you can start with relatively few such results,” Adam says. “Every time you run the loop, you throw away at least one extra result that speeds up the reaction and makes it even faster.”

Autocatalysis is similar to rabbit population growth. Pairs of rabbits come together to create new rabbit babies, and then the new rabbits grow and mate to create more rabbits. You don’t need too many rabbits to have many more rabbits soon.

But searching the universe for floppy ears and furry tails probably isn’t a winning strategy. Instead, Cachar hopes chemists will take ideas from the new study’s list of recipes and test them in pots and pans that mimic extraterrestrial cuisines.

“We will never know exactly what caused life to arise on this planet. “We don’t have a time machine,” says Kachar. “But in a test tube, we can create multiple planetary conditions to understand how life-sustaining dynamics might have evolved in the first place.”

Kachar leads a NASA-supported consortium called MUSE, which deals with the use and selection of metals through the ages. His laboratory will focus on reactions, particularly the elements molybdenum and iron, and he looks forward to seeing others cook up the more exotic and unusual parts of the new recipe book.

“Carl Sagan said that if you want to make a cake from scratch, you have to create the universe first,” says Kachar. “I think if we want to understand the universe, we should make some pies first.” Source