Were hot, humid summers the key to life's origins?

Were hot, humid summers the key to life's origins?
A new study from the NSF-NASA Center for Chemical Evolution reports a possible model for how biological polymers may have formed during the origin of life on Earth. Credit: Bracher Lab, Saint Louis University.

Uncovering how the first biological molecules (like proteins and DNA) arose is a major goal for researchers attempting to solve the origin of life. Today, chemists at Saint Louis University, in collaboration with scientists at the College of Charleston and the NSF/NASA Center for Chemical Evolution, published a study in the journal Nature Communications that suggests deliquescent minerals—which dissolve in water they absorb from humid air—can assist the construction of proteins from simpler building blocks during cycles timed to mimic day and night on the early Earth.

"In terms of the history of the planet, how life originated is probably the greatest scientific question we can ask," said Paul Bracher, Ph.D., assistant professor of chemistry at Saint Louis University and principal investigator of the study. "A key piece of this grand challenge is figuring out how big polymer molecules we know to be important for life could have formed before all of our biological machinery evolved to make them."

Baking Proteins in the Prebiotic Kitchen

Amino acids are the molecular building blocks linked together by peptide bonds to form proteins. Chemists have long known that simply baking mixtures of amino acids to dryness will lead to the formation of . The yields of peptides improve when water is added and the sample is dried again, after the ingredients are allowed to re-mix. Subjecting amino acids to repeated wet-dry cycles could have been a good recipe for cooking up peptides and proteins on the early Earth, as hot sunny days interrupted by the occasional rainstorm seem like reasonable weather patterns. But a major criticism of this process is its reliance on unpredictable storms that may have watered-down the ingredients to excess.

Water: A Necessary But Problematic Ingredient

"Follow the water" has been NASA's motto in the search for life outside our planet. Without water, the biochemistry of life as-we-know-it would be impossible.

In chemistry, the solution is often the problem. For constructive chemical processes to occur, the building blocks must dissolve in a liquid solution to find partners to react. On Earth, this medium is water, the solvent of life.

However, water can be a double-edged sword. While life needs water to survive, too much water can be destructive. Most biological molecules are prone to hydrolysis, a process in which water breaks apart chemical bonds. And too much water will eventually flood developing cells that contain the evolving biomolecules, strewing them too far away from each other to react.

A Pinch of Salt

Deliquescent minerals offer a means to side-step the limitations of traditional wet-dry cycling. These salts absorb a limited amount of water from the air, based on the relative humidity, offering natural regulation of the water present in a solution.

The new study—a collaboration between scientists at SLU and the College of Charleston—reports how deliquescent salts can assist making peptides from the simplest amino acid, glycine, during self-regulated, repeating wet-dry cycling. During the day, the reaction mixtures form peptides when they evaporate to dryness at high temperatures. At night, the reactions acquire water from the atmosphere to form aqueous solutions at low temperatures, thereby rewetting without the addition of water by a rainstorm and avoiding the possibility of destructive overdilution.

Seemingly minor differences, like changing the ambient humidity from 50% to 70%, can lead to profound differences in the tendency of samples to absorb water, and hence, large differences in the yields of reactions they host. And while potassium and sodium are neighbors on the periodic table with almost identical reactivities, many potassium salts are deliquescent where their sodium counterparts are not. The salt K2HPO4 fostered yields of peptides from glycine ten times greater than in Na2HPO4.

The team believes their system may provide clues relevant to solving the mystery of why all life on Earth spends so much energy enriching potassium inside cells and throwing sodium out.

"This creative research, exploring how the chemical environment regulates formation of large molecules, represents another major step toward CCE's goal of understanding the chemistries behind early biological molecules. Successful engagement of undergraduate researchers in this work also reflects NSF's mission of integration of research with education for the training of future workforce," said Dr. Lin He, the Acting Deputy Division Director for the Division of Chemistry at the National Science Foundation.

Bakeries Beyond Earth

Despite their exotic-sounding name, deliquescent salts are common and exist in natural settings where they can play a role in enabling liquid water to exist in environments that are otherwise too cold and/or dry.

In a hyper-arid region of Chile's Atacama Desert that is inhospitable to life, microbial communities reside in deposits of the mineral halite. Their photosynthetic activity spikes when the rises above 70%, exceeding the threshold where their halite environment becomes deliquescent.

Deliquescent mixtures of chloride and perchlorate salts have also been identified on Mars. These mixtures appear to flow seasonally and have garnered significant interest from astrobiologists as the only liquid on the surface of the planet.

Making use of these naturally occurring minerals, this new study proposes wet-dry cycles regulated by natural daily oscillations in temperature and humidity—not on uncontrollable rain events—constitute a prebiotically feasible model for driving the chemical formation of biopolymers central to biology.

Was a simple pinch of salt the missing ingredient for cooking up life on Earth? We may never know for sure, but in this case, it certainly seems to make a great improvement to the recipe for baking proteins.

Explore further

Origin of life insight: peptides can form without amino acids

More information: Campbell, Thomas D.; Febrian, Rio; McCarthy, Jack T.; Kleinschmidt, Holly E.; Forsythe, Jay G.; Bracher, Paul J. "Prebiotic Condensation Through Wet-Dry Cycling Regulated by Deliquescence." Nature Communications (2019). dx.doi.org/10.1038/s41467-019-11834-1
Journal information: Nature Communications

Citation: Were hot, humid summers the key to life's origins? (2019, October 4) retrieved 17 October 2019 from https://phys.org/news/2019-10-hot-humid-summers-key-life.html
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User comments

Oct 04, 2019
Wet-dry cycles are all very interesting. But that's not what goes on in any known cell. Metabolism is *always* wet.

Oct 04, 2019
"...can assist making peptides from the simplest amino acid, glycine,"
So the peptides made were all repeats of a single amino acid? And they started with a good supply of glycine, without other amino acids? And the whole process goes south if exposed to some rain? Jayarava has a point, too.

Sounds like a stretch to go from this research to talking about how life might have begun.

And according to one commentator on another report, we already know life began near an undersea hydrothermal vent so all these land-based theories are moot.

Pardon me for being skeptical about the whole idea.

Oct 05, 2019
" Metabolism is *always* wet. "

"life began near an undersea hydrothermal vent"

psst... don't tell the panspermia nutbars
they have their hearts set on
living organisms surviving billions of years
of exposure to desiccating vacuum & radiations

Oct 05, 2019
Bacterial endospores, fungal spores, tardigrades, viruses, bdelloid rotifers, nematodes, plant seeds, brine shrimp eggs, and the larvae of an insect known as the sleeping chironomid can all survive dessication and rehydration, a phenomenon Jayarava has just assured us is not possible. Billions of years is a bit of a stretch, but there's strong evidence of organisms being revived after millennia of dehydration.

Oct 05, 2019
To answer the headline, no, hot summers won't give you life. To even suggest that some simple thing like this could bring on life shows that the authors have no idea how complex life is. Please move on, acknowledge that there could be a Creator God, and then enjoy the real science of exploring and finding out how He made this world and universe of order and laws.

Oct 05, 2019
well bm, you listed a whole lot lifeforms that are hypothesized
may possibly survive exposure to desiccating vacuum & constant radiation bombardment

however, you did not offer a link tp a verified. peer-reviewed research that proved that hypothesis

& please, no fake-science fiction
or unproven speculations
or wishful thinking
or excerpts out of context
from failed experiments

tell you what, forget about billions of rears or millions
or even centuries

come up with one, confirmed, verified, peer reviewed
laboratory experimental research project
that kept the specimens
sealed in real vacuum
for ten years
with a healthy dose of ionizing radiation

then successfully revived the little critters back to Earth environment
& the spores/eggs/seeds/larvae hatched, flourished, reproduced

much less reviving adult bugs that will thrive across multiple generations

you noticed i used the term
"back to Earth environment"?
what other planetary surface is proven to feed &support Earth bugs?

Oct 07, 2019
can all survive dessication and rehydration, a phenomenon Jayarava has just assured us is not possible.

That's not quite what I said. I said "metabolism is always wet". That is, the *inside* of a living cell is always a watery environment. When cells are dessicated they either have to retain water by closing the pores in their membrane, or suspend metabolism. Either is fine, but neither contradicts my initial statement.

Moreover there is no evidence of such peptides occuring in nature. The Atacama desert is mentioned, but they talk about existing cells surviving, they don't mention finding any spontaneously generated peptides. I'm not sure anyone has ever found abiogenic peptides in nature, so please direct me to the research on that.

Oct 07, 2019
I cannot find any reference to abiogenic production of peptides outside cells. Maybe I don't have the right keywords?

If it happened abundantly enough in the past to spark life, then we'd need some theory about why it stopped happening. And this wet/dry thing doesn't seem to offer that. According to this we ought to be finding "free-living" peptides in nature.

Again please direct me to evidence of peptides forming outside of cells in nature now, or any evidence of it happening in the past that also explains why it doesn't happen now.

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