The Outside/In[box]: Was The Origin Of Life A Singular Event?
Every other Friday on Morning Edition, the Outside/In team answers a question from a listener about the natural world.
This week, Bill from Lyme asks: “Does anyone know if the origin of life was a singular event, or was there a particular period in earth’s development that spawned the creation of life in multiple places? Is there any evidence [that] process may still be going on somewhere on or under the earth at this time?”
The Primordial Question
In an 1871 letter to the English botanist Sir Joseph Dalton Hooker, Charles Darwin speculated about the origins of life on Earth, writing that perhaps it began “in some warm little pond with all sorts of ammonia and phosphoric salts…”
Fifty years later, a Soviet biochemist named Alexander Oparin took that idea and gave it a more flavorful twist: he called it the primordial “soup.”
So, yes, there was a period when scientists think conditions on Earth were rich with the building blocks needed to spark life. But did it catch fire more than once?
The oldest direct evidence for life is fossilized colonies of microbial organisms preserved in layers of rock that go back a staggering 3.5 billion years. In order to have evolved to that point, the first organisms would have to have appeared hundreds of millions of years prior.
How and where exactly that happened is still a matter of debate, but it’s definitely possible lightning struck more than once.
Stirring the Pot
The ingredients in that primordial soup might be familiar to you: things like proteins, lipids, and even RNA, the biological information storage system that’s similar to DNA.
Even though these might be things we associate with living organisms, these organic molecules can also exist outside the living world. In fact, one of the ways they would have been added to the primordial soup was through meteorites and asteroids smashing into the planet’s surface during “The Late Heavy Bombardment”.
Some scientists theorize that the primordial soup that spawned life was brewed in deep underwater ocean vents, while others think it was more likely to have been cooked up in pools near hot springs and geysers.
Either way, these ingredients are required to kickstart some of the essential processes of life: metabolism (the conversion of energy into life-sustaining activities) and the ability to pass down information from one generation to the next (i.e. evolution).
Luke Steller prefers the geyser theory. He’s a Ph.D. student and educator at the Australian Center for Astrobiology at the University of South Wales in Sydney, where he’s trying to recreate conditions similar to that early primordial soup. He likes the idea that it wasn’t a singular moment.
“It’s a good chance [life] might have popped up more than once in that really fertile period [when molecular building blocks were being delivered to Earth via meteorites]” explains Luke.
But Luke also says it’s helpful to think about it from another perspective.
Picture the most complete family tree there is, in which all of the living organisms on Earth - plants, animals, fungi, everything - branch out from the single trunk, when life on Earth first began. This is sometimes called “the tree of life.” The trunk, where all of the organisms eventually meet, is called the LUCA - or “Last Universal Common Ancestor.”
“You can also imagine that tree of life having an interconnected root system underneath it,” Luke says. “So you would have had all these different chemical processes, RNA in one pool, and metabolism in the other, coming together and eating each other… collaborating together, and eventually forming that one bottleneck LUCA. That would’ve then evolved out of that bottleneck into everything else.”
So life (or its chemical building blocks) might have sparked more than once, only to get eaten and wind up as part of the same original organism from which all life as we know it now stems.
Soup to Nuts
Now, to quickly answer Bill’s second question - could it happen again today? Probably not.
The days of the primordial soup are largely over. The oxygen created by the explosion of life (which really went nuts around 2.2 billion years ago) is destructive to some of those organic molecules needed to kickstart the process. And, even if it were to get going, good luck surviving in a world that’s now full of hungry predators.
“There’s no bubbling pools full of organic RNA and all that stuff,” Luke says, “because a little bit of bacteria will come and chomp that right up.”
That being said, Bill was on to something: Luke did mention the possibility of a “shadow biosphere” deep under the Earth’s crust, where there could be different forms of life completely unrelated to our own family tree.
Mole people? Lava worms? Probably not, but who knows! Guess it’s time for another sequel to Journey to the Center of the Earth.
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