The genetic code of every living thing that we know of is made up of four DNA bases. But how did those bases get here? How did they originally form? Did we come from outer space somehow? Thanks to an ultra-high-powered-laser and some Czech scientists, now we've at least got a clue.
The finding suggests adenine, guanine, cytosine, and uracil (found in RNA and a very close relative of thymine, the fourth DNA base) could have all formed here on Earth, and means it's at least possible that we're not all aliens.
Where did the alien idea come from? Back in 2011, NASA researchers noted that they'd found adenine and guanine (but not thymine and cytosine) in meteorite samples, which led to a new push of an already popular hypothesis that the building blocks of life came here from space in some way.
But Martin Ferus of the Academy of Sciences of the Czech Republic and his colleagues say that DNA could have been formed here on Earth, all at the same time, during the Late Heavy Bombardment period. In fact, they've recreated the specific conditions needed in the lab, which apparently were quite common back in the day (like, 4 billion years ago back in the day).
As you might expect, during this period Earth was getting hit with asteroids and other large objects at a much higher rate than usual. The high temperatures and massive energy generated by the impacts, when combined with standard clay and formamide—a corrosive liquid that's believed to have been present in large quantities during the Late Heavy Bombardment—created all four DNA bases in fairly large quantities, Ferus theorized. In Ferus's scenario, asteroids only conveyed the energy necessary to create DNA—they didn't bring the nucleobases here themselves.
"The high-impact activity may not have been harmful for the formation of biomolecules and the first living structures," he wrote in a paper published in Proceedings of the National Academy of Sciences. "Conversely, it may have been the source of energy required to initiate chemical reactions, such as the synthesis of biomolecules."
Where DNA originally came from has been one of the biggest mysteries in origin-of-life research, and Ferus's explanation is as compelling as any we've got so far. To prove that this indeed was a possibility, he and his colleagues set up an experiment in which they blasted meteorites, clay, and formamide with a very high powered laser called the Prague Asterix Laser System.
These conditions, Ferus wrote, are similar to what the Earth was like billions of years ago. The plasma created by the high energy of the impacts, when combined with clay and formamide in a body of water "could initiate a cascade of chemical reactions, eventually leading to the formation of the nucleobases."
"When formamide was irradiated [in the lab] in the presence of clay, all four bases were detected," he wrote.
He also suggested that maybe life on Earth is a cosmic coincidence, but not one that required life to actually come here from somewhere else.
"All of these findings suggest that the emergence of terrestrial life is not the result of an accident," he wrote, "but a direct consequence of the conditions on the primordial Earth and its surroundings."