Comet strikes may have delivered the building blocks of life to early Earth, a new study has revealed. Furthermore, it now appears that life may not have emerged on Earth at all without comet impacts in the formative period of Earth’s younger years.
According to the new study, at least 20 percent of xenon, a noble gas found in Earth’s atmosphere, got to Earth via comets in the distant past. Besides the xenon, researchers note that the comets most likely delivered other material to Earth as well.
As reported by Space this week, lead author Bernard Marty, a geochemist at the University of Lorraine and the Centre de Recherches Pétrographiques et Géochimiques in France, said that the “cometary contribution could have been significant for organic matter, especially prebiotic material, and could have contributed to shape the cradle of life on Earth.”
By analyzing xenon-isotope data gathered by the European Space Agency via its Rosetta space probe when it was in orbit around comet 67P (technically: 67P/Churyumov–Gerasimenko) in 2016, researchers found that the comet was deficient in heavy xenon. (Basic science: Isotopes are versions of an element, like xenon, that where the nuclei include different numbers of neutrons. Isotopes are designated “heavy” when they contain”Heavy” more neutrons, as compared to “lighter” isotopes.) But what made the find more interesting to the research team was that the comet’s xenon isotope composition was a match for a signature of atmospheric xenon found on Earth whose origin had heretofore been a mystery.
Marty and his team are convinced that there is a connection between comets and the emergence of certain elements on Earth.
“These findings establish for the first time a genetic link between comets and the atmosphere of the Earth,” Marty told Space.com in an email. “This link is not only qualitative but also quantitative, as it permits [us] to decipher for xenon what was the proportion of cometary Xe added to the Earth relative to asteroidal (meteoritic) Xe.”
According to the researchers, the xenon delivered by comets makes up 22 percent of that present on Earth. Asteroids contributed the rest. In fact, scientists believe that asteroids contributed a majority of the water that exists in Earth’s oceans as well as delivering most of the planet’s other “volatiles”– substances that exhibit low boiling points, such as nitrogen, carbon dioxide, and noble gases, like xenon. The evidence for this line of thinking derives from the similarities found between isotopes of Earth hydrogen, nitrogen and other materials and that of asteroids called carbonaceous chondrites.
To get an idea of just how many asteroid and comet impacts the Earth must have had to endure in its early development just to enter into formulating the chemical mix that would eventually make up the Earth and its atmosphere, consider that a NASA scientist evaluating what it would take to terraform Mars to make it habitable found that it would take a bombardment of 10 million comets made up of pure carbon dioxide just to get things started. Also, that is in addition to the carbon dioxide already present on Mars.
The new study’s findings also will prompt scientists to rethink how the early Solar System formed. Current models indicate that the outer Solar System, the area where comets form, was isolated early on from the inner. That may not have been the case.
So there is now evidence that the xenon isotope found on comet 67P is interstellar in origin, because it predates the formation of the Solar System. This discovery led the researchers to conclude that retrieving a sample of cometary material was of the “highest priority.”
The study of the data from comet 67P has been published in the online journal Science.
[Featured Image by ESA/Getty Images]