We’ve known how humans and pretty much all other complex species arose on this planet for a while now. The Theory of Evolution has that covered. But what evolution fails to explain is how life itself emerged from simpler chemical building blocks in the first place. That has been one of the most pervasive mysteries in the history of science—until now.
From non-living matter to life?
Well, the main question for scientists exploring the topic has to do with what is known as abiogenesis, the natural process by which life arose from non-living organic compounds. Up until now, scientists had been in the dark on a number of things regarding this process.
For example, they knew that at some point, a very simple single-cell organism started moving around, probably born out of the “primordial soup,” a mixture of chemicals that had the conditions to produce living beings during the Earth’s early years. In short, we know that life arose about 3.5 billion years ago as the first proteins came together and started self-replicating in the form of RNA and DNA. How that actually happened, however, we had no clue.
The basics
But now, a team of researchers at the University of Washington have come across a marvelous discovery. To understand it, however, we must first take a look at the basics.
We know all complex living beings are made up of tiny cells. All these cells have at least three essential things in common: first, there are molecules that encode information and undergo a copying process (i.e. DNA and its simpler counterpart, RNA). Second, there are proteins that perform crucial tasks as a sort of workforce. And third, there’s a membrane composed of fatty acids.
Before the first cell even arose, there was a more basic form of near-living object, which scientists call a “protocell,” which is basically the ancestor of all living things and the bridge between living and nonliving objects.
These protocells had the three elements mentioned above: proteins and RNA in a membrane. Membranes are like little bags that keep everything together: without membranes, RNA, DNA, and proteins would just go their own way without ever producing a living system.
So, what’s the problem?
The thing is, the conditions of early Earth would’ve made it very difficult for a membrane to actually last long enough to allow RNA and proteins to do their thing. Salts, for one, can destroy the fatty acids that make up membranes in the first place, and any early chemical compound billions of years ago was likely filled with salt.
Certain ions like magnesium and iron causes the spherical protocells to collapse as well, but RNA needs ions to operate. That’s right: the very conditions for life, and the very elements needed for it to function, are also the things that would destroy any early attempt for life to emerge.
“Cells are made up of very different types of structures with totally different types of building blocks, and it has never been clear why they would come together in a functional way,” said Roy Black, one of the paper’s authors. “The assumption was just that — somehow — they did come together.”
But that’s not really a satisfactory explanation. In fact, saying “it just happened” is no explanation at all. So, how did it all actually take place?
The ultimate answer
That’s where Caitlin Cornell, Sarah Kelle, and the rest of the research team comes in. The key lies in the building blocks of proteins themselves, and the order in which you make the recipe. As the paper outlines:
“How did the first cells on Earth arise? In a minimal cell, a membrane separates proteins and RNA from the surrounding aqueous environment. Cell-like membranes spontaneously assemble from simple prebiotic surfactants called fatty acids. However, fatty acid membranes are unstable in solutions containing salts that were likely present in environments of the early Earth. We find that amino acids, the building blocks of proteins, bind to fatty acid membranes and stabilize them against salts.”
In other words, as long as the protocells and their membranes are in the presence of amino acids as they get hit with salts and ions, they’ll retain their structure. Certainly, pouring salt and then amino acids would destroy the tiny spheres, but if amino acids come first, everything works out.
Credit: Roy Black/Sarah Keller
So it’s truly a team effort: amino acids stick to the membranes and make them stable, while the membranes keep amino acids together to form proteins, and thereby life. This dance kept going for billions of years, as the interactions became more and more complex, giving rise to cells, plants, dinosaurs, rodents, apes, and finally humans.
A wonderful finding
And there it is: the origin of life can be traced back to nothing but simple chemistry. A truly elegant explanation. This gives us a crucial piece that was missing from the puzzle, and we’re now understanding more than ever what it took for one of the most marvelous phenomena in the universe to begin—an explanation which up until now had remained only within religious speculation.
The process described in the paper is magical, showing even how cellular structures arose in protocells, with rings inside rings or spheres inside spheres. The next step is to figure out just how these protocells bonded to form bigger, more complex molecules. But that’s a story for another day.
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