A spoonful of carbon, a sprinkle of hydrogen and a dash of cyanide -- this could be a snippet of the recipe for life's building blocks. Yes, you read that correctly. Cyanide.
Over the course of history, cyanide has deservedly earned its reputation as an immensely toxic poison. It's use as a biological weapon dates back to the Franco-Prussian war in the late 1800s, all the way to both World Wars, and some evidence supports its role in the Iran-Iraq war. It has even permeated pop culture, aka the famous spy movie trope of offering it to secret agents who foresee a choice between betrayal and death.
But in a paper published Thursday in the journal Nature, a crew of chemists suggest that while cyanide ends life as we know it, it could've helped evolve life from the early Earth, around 4 billion years ago. Back then, the world looked very different. The oxygen we breathe, for instance, didn't yet exist.
"Cyanide is poisonous to the type of biology we work with today," said Ramanarayan Krishnamurthy, a chemist at Scripps Research Institute in California and lead author of the study. "But it may not be poisonous if biology knows how to handle it."
In a lab, he and fellow researchers basically mixed together a bunch of molecules present on early Earth and popped some cyanide into the goop.
Ironically, the dangerous stuff helped synthesize the simplest components of life -- under moderate reaction conditions and with relatively few steps. It was all surprisingly straightforward. "That kind of scares you sometimes, when it is so simple," Krishnamurthy said. "We had this checked by three or four different people to ensure we did have the correct interpretations."
The team says its unique mechanism marks the "very first demonstration" of this sort of biological pathway to life's roots -- and one much simpler than its widely accepted, non-toxic counterpart that requires extreme reaction conditions, complex steps and a touch of trust.
What really happened 4 billion years ago?
Flashback to science class: "primordial soup," aka the buckets of various molecules once swirling freely in the early Earth's oceans.
Experts have long believed this elemental stew forced molecules to interact and form complex compounds, which then mingled, and many steps down the line, gave rise to simple organisms. Way (way) later, all that stuff turned into us.
One important feature in this saga is -- prepare for a mouthful -- the reductive Tricarboxylic Acid cycle, or r-TCA cycle. This eight-step biological process uses proteins to form compounds that sustain life. In short, it's considered essential for life today, so experts think it was likely vital for life long ago, firing away in the primordial soup.
But here's the problem: the early Earth's environment wasn't ideal for r-TCA. Oxygen wasn't around when our orb was younger, neither were the proteins that push the cycle along. Scientists often say certain metals could've got things going, but that'd have needed extreme conditions, such as super high heat. And I mean extreme.
So much so, Krishnamurthy explains, not only are those conditions unlikely to have existed on early Earth, they also prevent scientists from mimicking ancient r-TCA in a lab, step-by-step. Chemists have to sort of throw everything together, apply the conditions, wait and watch.
While such experiments do yield r-TCA compounds, it's difficult to prove they truly came from the cycle. Essentially, it's unclear whether r-TCA really happened 4 billion years ago.
In an effort to demonstrate an alternate reductive cycle that makes life's starter compounds, Krishnamurthy ran the experiment with cyanide in place of the troublesome metals. Remarkably, he found the molecules followed the same path as r-TCA, step-by-step, but with fewer overall stages and under much milder conditions.
It seemed to tell the story of early Earth life in a significantly easier way.
Although, the researchers are taking their results with a grain of salt. Krishnamurthy says "cyanide is thought to have been present on early Earth, though there has been no direct evidence it did because it's a reactive molecule that could have been consumed."
Biology has a past
Regardless, the team's results terrifically underline Krishnamurthy's ideology: "What biology does today is what biology does today. It need not be what biology was based on 4 billion years ago."
Krishnamurthy paints a wonderful analogy on how to digest the concept.
Imagine bringing someone from a remote village, who only knows how to construct houses with bricks and a few builders to New York City. They'd look up at the skyscrapers in awe and perhaps ask you how these metal towers could possibly have been made.
What they're missing, though, is these skyscrapers weren't made from bricks and definitely not by a small group of construction workers. They were made from steel, using cranes and huge pieces of equipment. "We are looking at biology now, which is this huge, beautiful building," Krishnamurthy said. "But we do not know how it was constructed and what was there before which allowed it to happen."
If there was enough cyanide on early Earth, life might very well owe itself to what we've now accepted as poison. And taking it a step further, if extraterrestrial organisms exist on other planets, perhaps cyanide had a hand there, too.
"We are letting chemistry tell us," Krishnamurthy said. "Rather than assuming we already know what biology should've been 4 billion years ago.