He hoped the experiment would be the key to unlocking the origins of life. But almost 70 years on from the experiment we still don’t have the answer.
Figuring it out is going to take some serious detective work. Even the timing is uncertain.
All we know for sure is that life began sometime between the formation of Earth 4.5 billion years ago and the oldest confirmed fossils 3.4 billion years ago. That leaves a window of 1.1 billion years.
Some people think life could have come to Earth from somewhere else in space, a concept with the slightly off-putting name of
panspermia.
The idea is that life travelled to earth via a meteoroid or some other kind of space body, from another planet. Somehow surviving the hostile environment of space and the crash landing here on Earth to begin our evolution.
But that doesn’t seem very credible since we have no evidence for any life elsewhere in the cosmos, and it doesn’t help us answer the fundamental question of how life arose in the first place.
Darwin wondered if life began in a “warm little pond” but the first serious theory about the origin of life was called the primordial soup. Scientists thought w hen Earth was young, the oceans were filled with simple chemicals needed for life, and eventually they assembled themselves into simple living cells.
Then came Stanley Miller’s experiment. And while it didn’t create life itself, it did produce amino acids – the building blocks of proteins.
Further experiments showed that amino acids could assemble themselves into proteins when they’re heated up. Proteins perform lots of essential functions in living organisms, such as acting as enzymes that speed up chemical reactions.
But the idea that proteins started life on their own has now been largely rejected. Life has to be able to reproduce, and that means that you need molecules that can copy themselves. The strongest candidate is RNA.
RNA
is a similar chemical to DNA, but it can also fold up and act as an enzyme, just like a protein. RNA is not as good for storing information as DNA, and it’s not as versatile as proteins, but it is a bit of a molecular jack of all trades.
So, it seems more likely that the first life forms were based on RNA, and DNA and proteins came later.
But in a lab, we find RNA needs a lot of help to assemble or copy itself, so chances are
it probably wasn’t enough
to start life on its own.
As far as we know, life can’t exist as chemicals in a soup. All living things we know of are made of cells that package up the chemicals.
So some scientists reckon the first organisms were made up of oil droplets or bubbles that acted like primitive cells, providing the structure for life to get going.
In the lab we can create droplets that
show life-like behaviour
, sensing and responding to their neighbours and moving towards “food” sources. A bit like Pac-Man.
Crucially though, these droplets can’t replicate or evolve, meaning, it’s unlikely that this guy is your ancient ancestor.
Finally, it has been suggested that life began with chemical reactions that extracted energy from the environment and used that energy to build the molecules of life. In other words,
metabolism came first
. This might have happened in hydrothermal vents at the bottom of the ocean, where energy from inside Earth heats the water up to 400C.
So, which came first: cells, metabolism, or genetics? It’s a bit of a chicken-and-egg conundrum. When any of these theories are tested out in the lab, none of the experiments produce anything particularly life-like.
The alternative is that life arose fully formed, with all these elements present right at the start. That might seem even more unlikely, but recent evidence has led some scientists to think that’s
exactly what happened
. The chemistry required involves ultraviolet light, and periodic drying, so the most likely location is thought to be chemical-rich pools on land.
So, the origin of life is still shrouded in mystery. Scientists have tried all sorts of experiments aiming to recreate life from chemicals in the lab. They haven’t gone all the way yet, but we’ve made lots of progress. Maybe one day soon, we’ll succeed in creating artificial life in the lab, which could tell us how our oldest ancestor came to be. What could possibly go wrong?
