Researchers from NASA's Goddard Space Flight Center in Greebelt, Md., report evidence that ready-made DNA parts could have crashed to the surface on objects like meteorites, and then assembled under Earth's early conditions to create the first DNA.
The discovery was made using samples from 12 carbon-rich meteorites, nine of them from Antarctica. The team extracted small fragments of the meteorite and ran them through a process to determine their structure. What they found was adenine and guanine. These are two of the nucleobases needed to make the rungs of DNA's spiral ladder (in addition to thymine and cytosine, which were not present in the sample).
The team also found hypoxathine and xanthine, which are not part of DNA but are used in various biological processes.
"People have been discovering components of DNA in meteorites since the 1960s, 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, lead researcher of the discovery. "For the first time, we have three lines of evidence that together give us confidence these DNA building blocks actually were created in space."
The team all but ruled out the possibility that the compounds were contaminated on Earth because the nucleobases they found do not naturally occur on this planet. Furthermore, the samples, predominately found in Antarctic ice, did not have the chemical makeup to support terrestrial contamination.
They studied both terrestrial and extraterrestrial samples to make the comparisons. Opponents of the idea that DNA particles came from space typically point to contamination of samples to question the theory.
What is particularly significant about the new research is that the scientists were able to effectively prove there was no contamination and that the biological parts were created in space and carried to Earth.
The research has even greater implications than first meets the eye.
If the ingredients for life were brought here from some external source, there's always the possibility that the same thing has happened elsewhere in the universe -- possibly many times over. This would give credence to the theory that life exists on other planets.
Though the findings are likely to undergo a lot more scientific scrutiny, if meteorites are truly bringing in the ingredients for life, it could forever change our picture of life in the universe.
The research was published in the Proceedings of the National Academy of Sciences.
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