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Comets may have seeded life on Earth

Chemists from the University of California at Berkeley have uncovered new evidence that comets may have seeded life on Earth. By simulating conditions in deep space, chemists from Berkeley and the University of Hawaii at Manoa reached the conclusion that complex dipeptides could have been generated on icy interplanetary dust and then brought to Earth, seeding life.

According to NASA, comets are cosmic “snowballs” of frozen gases, rock and dust approximately the size of a small town. When a comet’s orbit brings it close to the sun, it heats up and spews dust and gases into a large glowing head bigger than most planets. The dust and gases create a tail, pointing away from the sun, that can be millions of kilometers long.

The chemists demonstrated that conditions in deep space are capable of generating complex dipeptides that are essential building blocks of life. A dipeptide is a peptide chain which includes two amino acids. They can be found in nature and they can also be created in laboratory environments.

The discovery is evidence that these molecules may have been carried to Earth aboard a comet or possibly meteorites, activating the creation of proteins, enzymes and other complex molecules that are essential for life.

According to UC Berkeley chemist and coauthor Richard Mathies, it is “fascinating” to think that the most fundamental building blocks that led to life on Earth may have had an extraterrestrial origin.

Previously, chemists have located basic organic molecules, like amino acids, in several meteorites that have impacted Earth. However, they have not been able to locate the more complex molecular structures that are necessary for the formation of life. Prior to this study, scientists operated under the assumption that the more complex molecular structures must have originated in Earth’s early oceans.

“Our results indicate that the radiation-induced, non-enzymatic formation of proteinogenic dipeptides in interstellar ice analogs is facile. Once synthesized and incorporated into the ‘building material’ of solar systems, biomolecules at least as complex as dipeptides could have been delivered to habitable planets such as early Earth by meteorites and comets, thus seeding the beginning of life as we know it,” write the authors in the study’s abstract.

In an ultra-high vacuum chamber cooled to 10 degrees above absolute zero, Seol Kim and Ralf Kaiser of the Hawaiian team simulated a comet in deep space. They included carbon dioxide, ammonia, methane, ethane and propane. When they simulated the cosmic rays in space, the chemicals responded to form complex, organic compounds that are essential building blocks of life.

Across the Pacific, Mathies and Amanda Stockton then examined the organic residues using the Mars Organic Analyzer, an instrument that Mathies created for ultrasensitive detection and identification of tiny organic molecules in the solar system. Mathies’ instrument showed the presence of complex molecules capable of seeding life on Earth.

The study’s findings were recently described in detail in The Astrophysical Journal.