The origins of life may soon have an extraterrestrial explanation. NASA-funded researchers today announced that they had uncovered evidence that some crucial components of DNA found in asteroids did not originate on earth.
“People have been discovering components of DNA in meteorites since the 1960′s, but researchers were unsure whether they were really created in space or if instead they came from contamination by terrestrial life,” said Dr. Michael Callahan of NASA’s Goddard Space Flight Center in a press release. “For the first time, we have three lines of evidence that together give us confidence these DNA building blocks actually were created in space.”
For decades the scientific community had hypothesized that a chemical process inside comets and meteorites could create elements of DNA, or Deoxyribonucleic acid. The ladder-like molecule contains genetic “blueprints” needed to create life and living organisms. It’s made up of four different molecules, called nucleobases, which lock together rung-by-rung in the now-iconic double-helix shape.
Scientists point to three pieces of evidence supporting their claim. The first comes in the form of two of those nucleobase molecules, adenine and guanine, which they found in meteorites retrieved from Antarctica. The meteorites also contained trace amounts of three molecules similar in structure to nucleobases, two of which are “almost never used in biology.” These analogs, which seldom occur in nature, suggest that meteorites were essentially space-based chemistry labs that generated multiple variations of the nucleobase molecules.
“You would expect them to produce many variants of nucleobases, not just the biological ones, due to the wide variety of ingredients and conditions in each asteroid,” Callahan explains.
Scientists also ruled out the possibility that earth-based biological material contaminated the meteorites. Testing the surrounding ice, they detected few traces of the nucleobases and no trace at all of the analogs.
When the team attempted to recreate these nucleobases in a lab, they discovered that they were all created in a non-biological process, using “chemical reactions containing hydrogen cyanide, ammonia, and water.”
“There seems to be a ‘goldilocks’ class of meteorite … where conditions are just right to make more of these molecules,” adds Callahan.