Earliest life may have arisen in ponds, not oceans

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Primitive ponds may have provided a suitable environment for brewing up Earth's first life forms, more so than oceans, a new MIT study finds.

Researchers report that shallow bodies of water, on the order of 10 centimeters deep, could have held high concentrations of what many scientists believe to be a key ingredient for jump-starting life on Earth: nitrogen.

In shallow ponds, nitrogen, in the form of nitrogenous oxides, would have had a good chance of accumulating enough to react with other compounds and give rise to the first living organisms. In much deeper oceans, nitrogen would have had a harder time establishing a significant, life-catalyzing presence, the researchers say.

"Our overall message is, if you think the origin of life required fixed nitrogen, as many people do, then it's tough to have the origin of life happen in the ocean," says lead author Sukrit Ranjan, a postdoc in MIT's Department of Earth, Atmospheric and Planetary Sciences (EAPS). "It's much easier to have that happen in a pond."

Ranjan and his colleagues have published their results today in the journal Geochemistry, Geophysics, Geosystems. The paper's co-authors are Andrew Babbin, the Doherty Assistant Professor in Ocean Utilization in EAPS, along with Zoe Todd and Dimitar Sasselov of Harvard University, and Paul Rimmer at Cambridge University.

Breaking a bond

If primitive life indeed sprang from a key reaction involving nitrogen, there are two ways in which scientists believe this could have happened. The first hypothesis involves the deep ocean, where nitrogen, in the form of nitrogenous oxides, could have reacted with carbon dioxide bubbling forth from hydrothermal vents, to form life's first molecular building blocks.

The second nitrogen-based hypothesis for the origin of life involves RNA—ribonucleic acid, a molecule that today helps encode our genetic information. In its primitive form, RNA was likely a free-floating molecule. When in contact with nitrogenous oxides, some scientists believe, RNA could have been chemically induced to form the first molecular chains of life. This process of RNA formation could have occurred in either the oceans or in shallow lakes and ponds.

Nitrogenous oxides were likely deposited in bodies of water, including oceans and ponds, as remnants of the breakdown of nitrogen in Earth's atmosphere. Atmospheric nitrogen consists of two nitrogen molecules, linked via a strong triple bond, that can only be broken by an extremely energetic event—namely, lightning.

"Lightning is like a really intense bomb going off," Ranjan says. "It produces enough energy that it breaks that triple bond in our atmospheric nitrogen gas, to produce nitrogenous oxides that can then rain down into water bodies."

Scientists believe that there could have been enough lightning crackling through the early atmosphere to produce an abundance of nitrogenous oxides to fuel the origin of life in the ocean. Ranjan says scientists have assumed that this supply of lightning-generated nitrogenous oxides was relatively stable once the compounds entered the oceans.

However, in this new study, he identifies two significant "sinks," or effects that could have destroyed a significant portion of nitrogenous oxides, particularly in the oceans. He and his colleagues looked through the scientific literature and found that nitrogenous oxides in water can be broken down via interactions with the sun's ultraviolet light, and also with dissolved iron sloughed off from primitive oceanic rocks.

Ranjan says both ultraviolet light and dissolved iron could have destroyed a significant portion of nitrogenous oxides in the ocean, sending the compounds back into the atmosphere as gaseous nitrogen.

"We showed that if you include these two new sinks that people hadn't thought about before, that suppresses the concentrations of nitrogenous oxides in the ocean by a factor of 1,000, relative to what people calculated before," Ranjan says.

"Building a cathedral"

In the , and dissolved iron would have made nitrogenous oxides far less available for synthesizing living organisms. In shallow ponds, however, life would have had a better chance to take hold. That's mainly because ponds have much less volume over which compounds can be diluted. As a result, nitrogenous oxides would have built up to much higher concentrations in ponds. Any "sinks," such as UV light and dissolved iron, would have had less of an effect on the compound's overall concentrations.

Ranjan says the more shallow the , the greater the chance nitrogenous oxides would have had to interact with other molecules, and particularly RNA, to catalyze the first living organisms.

"These ponds could have been from 10 to 100 centimeters deep, with a of tens of square meters or larger," Ranjan says. "They would have been similar to Don Juan Pond in Antarctica today, which has a summer seasonal depth of about 10 centimeters."

That may not seem like a significant body of water, but he says that's precisely the point: In environments any deeper or larger, nitrogenous oxides would simply have been too diluted, precluding any participation in origin-of-life chemistry. Other groups have estimated that, around 3.9 billion years ago, just before the first signs of life appeared on Earth, there may have been about 500 square kilometers of shallow ponds and lakes worldwide.

"That's utterly tiny, compared to the amount of lake area we have today," Ranjan says. "However, relative to the amount of surface area prebiotic chemists postulate is required to get life started, it's quite adequate."

The debate over whether originated in ponds versus oceans is not quite resolved, but Ranjan says the new study provides one convincing piece of evidence for the former.

"This discipline is less like knocking over a row of dominos, and more like building a cathedral," Ranjan says. "There's no real 'aha' moment. It's more like building up patiently one observation after another, and the picture that's emerging is that overall, many prebiotic synthesis pathways seem to be chemically easier in ponds than oceans."


Explore further

Sulfites and bisulfites in shallow lakes may have set the stage for Earth's first biological molecules

More information: Nitrogen Oxide Concentrations in Natural Waters on Early Earth, Geochemistry, Geophysics, Geosystems, agupubs.onlinelibrary.wiley.co … 10.1029/2018GC008082
Citation: Earliest life may have arisen in ponds, not oceans (2019, April 12) retrieved 17 October 2019 from https://phys.org/news/2019-04-earliest-life-arisen-ponds-oceans.html
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Apr 12, 2019
Atmospheric nitrogen consists of two nitrogen ATOMS joined by a strong triple bond, not two "nitrogen molecules"! ! ! !

Middle school and high school students who have taken basic chemistry know this.

Apr 12, 2019
This makes sense in that a pond can provide less active physical environment and higher chemical concentrations...
Not to mention, a certain level of repetitive cyclicity...

Apr 12, 2019
A pond would have needed a source of fresh or slightly salty water to freshen it besides rain. It would also have needed a channel to empty the overflow. And a source of underground heat to prevent freezing in winter.
I prefer the ocean scenario in a protected cove near land, with an underwater volcano.

Apr 12, 2019
I would think that the UV light would be more effective in destroying nitrogenous compounds in a pond than in the ocean because the UV could penetrate all the way to the bottom of a pond whereas is could only penetrate the top layers of the ocean.

Apr 13, 2019
Atmospheric nitrogen consists of two nitrogen ATOMS joined by a strong triple bond, not two "nitrogen molecules"! ! ! ! Middle school and high school students who have taken basic chemistry know this.
The MIT original (currently) reads:
"Atmospheric nitrogen consists of two nitrogen atoms, linked via a strong triple bond, that can only be broken by an extremely energetic event — namely, lightning." I suspect Ms Chu corrected her copy, but phys.org doesn't proof their articles.

Apr 13, 2019
And a source of underground heat to prevent freezing in winter.
The time in question was around the Late Archean, when almost everywhere on Earth was warm at the very least.

Apr 13, 2019
Just want to say I TOLD YOU SO,
back last July 4th, 2018.
https://billymeie...e-ocean/
From Billy Meier, who knew it February 3rd, 1988.
Just added to the list of hundreds of things Meier printed in published copyrighted books years and decades before all the scientists.
Time for you all to see what else you don't know about science and space.

Apr 14, 2019
So, we are all pond scum!

Apr 14, 2019
So, we are all pond scum!
Or just scum.

Apr 14, 2019
It is laughable that any scientist would think the amazing thing we call life could come from a 10cm pond because it has some nitrogen in it. It is superstition and a myth, nothing more.

Apr 14, 2019
It is laughable that any scientist would think the amazing thing we call life could come from a 10cm pond because it has some nitrogen in it. It is superstition and a myth, nothing more.


Lol. Says an idiot that believes in all-seeing sky daddy!

Apr 14, 2019
Life as we know it is nothing but carbon chemistry. There is no need to suppose anything mystical about it. Energy gradients, abundant carbon and other common elements, stable aqueous environments, and lots and lots of time. No magic. Just chemistry.

Apr 15, 2019
It is laughable that any scientist would think the amazing thing we call life could come from a 10cm pond because it has some nitrogen in it. It is superstition and a myth, nothing more
Just saying something is true doesnt make it true you know?

Only 2 places where that happens - the psychotic brain and the religionist brain. Must be the same brain.

Apr 15, 2019
Interesting constraints, but the conclusions seem a far reach. On the plus side, I note familiar astrophysicist and excellent early planet hunter D. Sasselov is one of the authors.

When biochemists analyze early habitability they will inevitably conclude that concentrating catchment systems to ponds, often in combination with evaporation, are more akin to their own test tubes in getting reactions going. They also set an artificial time limit at 4 Ga, perhaps considering the hypothesis of a Late Bombardment [ https://www.natur...-01074-6 , https://www.natur...8-0564-3 , https://phys.org/...lar.html ].

- tbctd -

Apr 15, 2019
- ctd -

When the mainstream of biologists and geologists study the problem, they conclude from evolutionary evidence that life evolved in ocean hydrothermal vents [ https://www.natur...l2016116 ] where coincidentally pore systems can concentrate dilute chemicals 1000 times for every mm pore. The integrated evidence is that life can have evolved early on [ https://www.natur...8-0644-x ], perhaps before there were any plate tectonic continents (but perhaps volcano islands)..

That said, this paper that concentrates on the late 4 Ga of climate, also neglects the early high surface UV irradiation that an anoxic atmosphere would allow. They also neglect that ammonia will be produced from N2 in vents exactly when the NOx concentration is low [ https://www.ncbi..../9759725 ].

@TGO: What we call evidence religionists call 'laughable'. Likely because the facts laugh at them: the universe is now known to be 100 % mechanistic.

Apr 15, 2019
To be precise, the article discuss a result where it is shown *not* a myth that life could have evolved in ponds. But the myth is that it could not - which the comment you cite evidently peddles in. Oy vey, religion dies hard - though I note even US is moving rapidly in the direction away from the Bronze Age invention of The Asylum and towards The Enlightenment of the modern world.

The problem is - AFAIK - not the CHNOS or metal components of a biochemical machine cell, such sources were abundant on Earth and we can see life evolved. Even if the paper show we do not know all the sources and sinks yet. Or even if there were any ponds at all!

The problem is the P component in CHNOPS. It is very hard to find mineral sources, even in vents, a condition current, often P limited, biomes can attest to!

Apr 15, 2019
Scientists believe that there could have been enough lightning crackling through the early atmosphere to produce an abundance of nitrogenous oxides to fuel the origin of life in the ocean.

Since all the ingredients were there, it could just as well have originated in the atmosphere.

Apr 15, 2019
Oy vey, religion dies hard - though I note even US is moving rapidly in the direction away from the Bronze Age invention of The Asylum and towards The Enlightenment of the modern world.


Don't be too disparaging, the ignorant few are often the loudest attention seekers and shouldn't negatively reflect on the rest of us. (To clarify, speaking as someone from the US, NOT as a religionist.)

Apr 15, 2019
@TGO: What we call evidence religionists call 'laughable'. Likely because the facts laugh at them: the universe is now known to be 100 % mechanistic
-Cue my favorite quote...

"Reason is a whore, the greatest enemy that faith has; it never comes to the aid of spiritual things, but more frequently than not struggles against the divine Word, treating with contempt all that emanates from God." -the godlover/jewhater martin luther

Apr 17, 2019
It is truly amazing that so many people, most who think they are so extremely intelligent, can't understand in God but they have no problem with life springing up circumstantially/spontaneously. Even if you add combinations of various elements you will indeed get some reactions of various types but once it's finished you will NOT have life. Go ahead, add any combination in the vacuum of space or simulated one and guess what? You get the same, various reactions but NO life. We can't even find life anywhere our probes have gone and one would think earth would have somehow seeped life out into/onto other planets.
So come on scientists of the world, give up all your theories of how life began and just agree it's naturally impossible, doesn't and won't happen. God and how ever you want to imagine him/her (He) is the source, He decided the type of planet all forms of life (plant, animal, human) would need to survive. So learn to life and believe in this alone.

Apr 18, 2019
can't understand in God but they have no problem with life springing up circumstantially/spontaneously
What makes you think it springs up spontaneously? What makes you think it isnt a fairly common and routine result of simple electrochemical processes?

Whats that? Because your priests say it doesnt? Well they have to earn a living too dont they?
Even if you add combinations of various elements you will indeed get some reactions of various types but once it's finished you will NOT have life
How do you know? Are you a chemist?
Go ahead, add any combination in the vacuum of space or simulated one and guess what? You get the same, various reactions but NO life
Again, how would YOU know?
We can't even find life anywhere our probes have gone and one would think earth would have somehow seeped life out into/onto other planets
And what percentage of the universe have we explored and in what detail?

Apr 18, 2019
Your book is all about people who never existed and events that never happened. Evidence tells us this. And so the god who wrote it is either an incompetent or a liar. And why would he LIE to you in order to find out how much you TRUST him?

And why would you ever trust such a lying incompetent when he tells you that in order to live forever all you have to do is accept the notion that anyone who doesnt believe in him cant be honest, or decent, or trustworthy?

IOW everything you ever wanted in return for being a bigot?

The universe may well have been created by a god. But it definitely wasnt YOUR god, that much is certain.

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