Exactly how life got started on Earth is still a mystery, but maybe we're looking for answers in the wrong place. Evidence is mounting that the building blocks of life were assembled in space and then delivered to Earth after new experiments managed to produce a key amino acid under simulated space conditions. This means we humans, and all other life on the planet, might have actually been aliens all along.
In trying to figure out just how matter transitioned from non-living to living, scientists have studied not just the ingredients for life, including amino acids and other complex organic molecules, but the recipe required to cook them just right.
"You just need the right combination of ingredients," says Michael Huels, an author of the new study. "These molecules can combine, they can chemically react, under the right conditions, to form larger molecules which then give rise to the bigger biomolecules we see in cells like components of proteins, RNA or DNA, or phospholipids."
The building blocks themselves are common here on Earth, but some of these, including amino acids and their precursor molecules, simple sugars, and other molecules with life-giving geometry, have all been detected in space, too. But the question of how these would form in such harsh conditions remained unanswered.
To find out, researchers from the Université de Sherbrooke in Canada recreated those conditions in the lab, blasting basic molecules with radiation to see how they might rearrange themselves into more complex ones. First, thin sheets of ice were composed of molecules of methane, ammonia and carbon dioxide, then placed in a chamber with an ultra-high vacuum and cryogenic temperatures.
Next, the team used an electron gun to irradiate these molecules, exposing them to the kind of low-energy electrons (LEEs) that they would readily encounter in space. And finally, the molecules that were created through this process were identified using a kind of mass spectrometry known as temperature programmed desorption.
Sure enough, the team was able to convert the basic molecules into intact molecules of glycine. This amino acid is made up of hydrogen, carbon, nitrogen and oxygen, and is a crucial component of life. One molecule of glycine was created for every 260 electrons that the basic molecules were exposed to. The next step was to calculate how likely a scenario this would be, for free-floating molecules out in space.
"You have to remember – in space, there is a lot of time," says Huels. "The idea was to get a feel for the probability: Is this a realistic yield, or is this a quantity that is completely nuts, so low or so high that it doesn't make sense? And we find that it is actually quite realistic for a rate of formation of glycine or similar biomolecules."
Of course, this doesn't confirm that life necessarily originated beyond Earth, but it does add more weight to the possibility that the first stages of life came together in space, before being delivered to Earth aboard meteorites and comets.
The research was published in The Journal of Chemical Physics.
Source: AIP Publishing