Cracking how life arose on Earth may help clarify where else it might exist

Jul 30, 2013
Elbert Branscomb is an affiliate faculty member at the Institute for Genomic Biology at the University of Illinois at Urbana-Champaign. Credit: Kathryn Coulter

Does life exist elsewhere or is our planet unique, making us truly alone in the universe? Much of the work carried out by NASA, together with other research agencies around the world, is aimed at trying to come to grips with this great and ancient question.

"Of course, one of the most powerful ways to address this question, and a worthy goal in its own right, is to try to understand how came to be on this planet," said Elbert Branscomb, an affiliate faculty member at the Institute for Genomic Biology (IGB) at the University of Illinois at Urbana-Champaign. "The answer should help us discover what is truly necessary to spark the fateful transition from the lifeless to the living, and thereby, under what conditions and with what likelihood it might happen elsewhere."

While many ideas about this fundamental question exist, the real challenge is to move beyond speculation to experimentally testable theories. A novel and potentially testable origin-of-life theory—first advanced more than 25 years ago by Michael Russell, a research scientist in Planetary Chemistry and Astrobiology at the NASA Jet Propulsion Laboratory—was further developed in a recent paper published in Philosophical Transactions of the Royal Society B (PTRSL-B), the world's first science journal, by Russell, Wolfgang Nitschke, a team leader at the National Center for Scientific Research in Marseille, France, and Branscomb.

Russell's hypothesis proposes that the transition to life was brought about by a peculiar geophysical and geochemical process called serpentinization—a process that played out on and just beneath the surface of our very 's ocean floor in the "Hadean" epoch more than 4 billion years ago.

One attractive aspect of the Russell hypothesis is that it provides potential explanations for several seemingly arbitrary and puzzling aspects of how all life on Earth works, including, most notably, how it taps into and exploits sources of energy. This process, quite oddly, involves constantly filling up and depleting a kind of chemical reservoir that is created by pushing a lot more protons onto one side of a membrane than the other—just like pumping water uphill to fill a lake behind a dam.

Then, mimicking how hydroelectric turbines are driven by water flowing downhill, these protons are only allowed to flow back "downhill" through the membrane by passing through a turbine-like molecular "generator," which creates, instead of high-voltage electricity, a chemical fuel called ATP, the cell's "gasoline." All cells then "burn" ATP in order to power their vital processes. The cells of air-breathing organisms, like us, "burn" ATP by ultimately converting oxygen to CO2.

Furthermore, while every bacterial cell has its own proton reservoir system, our bigger cells contain and cultivate herds of "ex-bacteria" (called mitochondria) that maintain their own reservoir, ATP-producing turbines, etc.—a trick of "agricultural domestication" at the cellular level that makes it not only possible for multi-cellular organisms to exist but to be huge, fast, and dangerous.

This "reservoir-mediated energy business" is not a minor undertaking of life, Branscomb notes. Every day our bodies produce and consume their weight in ATP molecules. In seconds, each newly made ATP molecule is used. In minutes, the body's entire ATP energy reserve is consumed and regenerated."That's why you can't stand to be without oxygen for more than a few minutes," Branscomb said. "We live on a thin, desperate edge to keep our metabolic motors running full blast. Yet in spite of this desperation, the process isn't carried out by using our energy sources directly, but by using the indirect, proton reservoir method. It's an arrestingly strange way of doing business that has made many scientists question why it is this way."The amazing answer, Russell's model suggests, is because that's how life got launched. "Before there was anything lifelike to take advantage of it, the geochemical process of serpentinization produced "for free" (along with much else of critical importance) two of the major components of this energy system: cell-like compartments surrounded by membranes and proton concentration differences on each side of the membranes," Russell said.

Thus, according to Russell's hypothesis, first life didn't have to make any of this stuff for itself. It was all a free gift of geochemistry on a wet, rocky, and tectonically-active planet.

"It's only later when life set out to take its act on the road that it had to figure out how to make its own membranes, pump protons uphill across these new membranes, tap into other sources of energy to do the pumping, etc.," Branscomb said. "But once hooked on the free stuff, the trans-membrane proton gradient in particular, life never broke the habit. And here we are, every living thing, still frantically pumping protons as if just staying alive depends on it—which it does."

Also notably, the Russell serpentinization hypothesis is founded directly on modern understandings regarding the physical nature of early Earth. In particular, at the time life arose, the world was almost entirely covered in a great, deep, and weakly-acidic ocean, the atmosphere was relatively oxidized and rich in CO2, and tectonic processes constantly replenished and destroyed the crusts of the ocean floor, as they still do today. And it is the exposure of newly made ocean crust to the ocean that gives rise to the geochemical magic of serpentinization.

As areas of new ocean crust cool, the still-stressed rock becomes brittle and develops cracks. Seawater gravitates down the cracks where it is heated and reacts chemically with rock minerals to form a highly-alkaline solution rich in hydrogen (H2) and methane (CH4), and containing molybdenum, a metal required by all life. This transformed water, or effluent, is then driven back to the surface, at a temperature of about 100 degrees centigrade, where, in Hadean times, it reacted with cooler, mildly acidic ocean water to create precipitates that form massive chimney-like towers similar to chemical gardens.

These highly-structured precipitate chimneys are comprised of a myriad of micro-compartments bounded by semi-permeable "mineral membranes." Across these membranes, a pH (i.e. proton) gradient arises between the extremely alkaline (~pH 11) emerging serpentine effluents and the surrounding, relatively acidic (~pH 5.5) ocean.

Magically, this pH gradient is almost exactly the same as the gradient that all living cells constantly recreate with the same strength and the same direction: acidic on the outside and alkaline on the inside.

"It is at least highly suggestive that every living thing is constantly and indeed furiously recreating something equivalent to this ancient 'ocean effluent' membrane-based proton gradient that serpentinization handed life to start with on the rocky floor of the ancient Hadean ocean," Branscomb said. "It was, in part, by exploiting that naturally-given, geochemical proton gradient that the engines required to produce the molecular 'starter kit' of life got going. So suddenly it's obvious why we pump protons and use this silly method—we became dependent on this 'free lunch' energy system when life was born, developed a lot of fancy machinery for using it, and have never severed that umbilicus since."

After Russell proposed this theory, scientists discovered a real-world example of an alkaline hot spring in the North Atlantic Ocean, famously called the Lost City. This geochemical edifice provides strong and detailed evidence in its structure and chemical properties for Russell's model that origin-of-life expert Nick Lane, a senior lecturer at University College London, has called the only credible theory to date.

One of the most important, and exciting, aspects of Russell's hypothesis is that the key ideas can, in principle, be tested. This just-released paper and its companion paper by Nitschke and Russell in PTRSL-B have advanced Russell's hypothesis and brought it substantially closer to experimental testing. To this end, Russell and his collaborators are currently making experimental model systems that recreate the serpentinization process, including the theory's mineralogical membranes and chemical gradients.

Branscomb, a member of the IGB's Biocomplexity research theme led by Swanlund Professor of Physics Nigel Goldenfeld, was funded in part by a recently awarded, five-year grant totaling $8 million from the NASA Astrobiology Institute. The grant funds the University of Illinois's Institute for Universal Biology, a member of the NASA Astrobiology Institute, which includes many members of the Biocomplexity theme who are studying the origin and evolution of life. Find out more about Illinois's Institute for Universal Biology and the IGB's Biocomplexity theme.

"We have a sample of only one planet known to harbor life," Goldenfeld said. "Thus it is critical that we be creative in extracting the most information from Earthly life as possible, if we are to ever understand the existence, likelihood, and nature of life elsewhere in the Universe. Russell, Nischke, and Branscomb's work lays an intriguing foundation for that endeavor, by cleverly bringing together concepts from thermodynamics, geochemistry and biology to advance a major new hypothesis for life's origins."

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verkle
1 / 5 (37) Jul 30, 2013
Mathematically it is near impossible (safe to say impossible) that life should suddenly come into being. Mathematically, it is even more impossible (if that can be said) that billions upon billions of amazing positive evolutional changes should happen to these first magical creatures.

We have to look elsewhere for the origin of life.
That part cannot be readily found by some of today's atheist scientists.

It is much more interesting, scientifically, to study today's creatures and find out more about how they are amazingly put together. That I call real science.

jsdarkdestruction
4.1 / 5 (26) Jul 30, 2013
verkle, rubbish. why don't you try reading about the miller experiment and tons of others on the possible origin of life instead of your bible? the bible is not real science. it is a bunch of myths and fairy tales.
kow
4.7 / 5 (20) Jul 30, 2013
Mathematically it is near impossible (safe to say impossible) that life should suddenly come into being. Mathematically, it is even more impossible...
...
It is much more interesting, scientifically, to study today's creatures and find out more about how they are amazingly put together. That I call real science.



I'd love to see your equations and mathematical models that makes you say that. Luckily science doesn't care about opinions. It only cares about theories, predictions and evidence. If your models prove that life can't rise from galactic dust then I call that science.
Andrew Palfreyman
1.6 / 5 (12) Jul 30, 2013
"Hadean" epoch => Hades!
serpentinization => Serpents!
The neolithic sheepshagger crowd (aka the Abrahamics) will have a field day with this.
Gmr
2.2 / 5 (13) Jul 30, 2013
"Hadean" epoch => Hades!
serpentinization => Serpents!
The neolithic sheepshagger crowd (aka the Abrahamics) will have a field day with this.

So, God actually favors pre-organic chemistry, that is the "pure" "Garden of Eden" was actually a chemical soup that had introduced into it the "fruit" of ATP - er, Knowledge...

God's message: become soup again.
deepsand
3.2 / 5 (26) Jul 31, 2013
Mathematically it is near impossible (safe to say impossible) ...

No, it is not "safe to say 'impossible.'" That is merely your uninformed opinion.
... that life should suddenly come into being. Mathematically, it is even more impossible (if that can be said) ...

It cannot be said. Impossible = probability vaue 0. There is no such thing as a negative probability.
.... that billions upon billions of amazing positive evolutional changes should happen to these first magical creatures.

The fact is that, given sufficient time, that which is not impossible is inevitable.

We have to look elsewhere for the origin of life.
That part cannot be readily found by some of today's atheist scientists.

Yet more uninformed opinion
It is much more interesting, scientifically, to study today's creatures and find out more about how they are amazingly put together. That I call real science.

Obviously you have no clue as to what "real science" is.
meBigGuy
4.2 / 5 (18) Jul 31, 2013
"Mathematically it is near impossible "

Actually, it has been shown that it is mathmatically very feasible. Based on the principle that the combinations deriving from failed mutations can be excluded. But, you won't hear that. Your mind is made up.
Also, the number of choices needed to get highly improbable results is much less than one would intuitively suspect.

I think in Wistar some idiot said the chances of life arising randomly was 1 in 10^350 (BTW, there are only 10^80 atoms in the Universe). He later recanted, but let's go with his number. It only takes 1163 correct decisions to resolve a 1 in 10^350 choice. That doesn't prove anything, only illustrates how small 10^350 actually is on a decision tree.

The supposed math arguments against the origin of life are all a joke. A distraction.

VendicarE
3.7 / 5 (12) Jul 31, 2013
"Mathematically it is near impossible (safe to say impossible) that life should suddenly come into being." - Verkle

Yes, and that is why life didn't spontaneously come to being. It took time for life to evolve from simple chemical reactions.

What fool told you that life suddenly came into being as if a 747 would spontaneously assemble itself?
antialias_physorg
4 / 5 (7) Jul 31, 2013
Mathematically it is near impossible (safe to say impossible) that life should suddenly come into being.

If you jump from 'mathematically near impossible' to 'safe to say impossible' then you might want to start over taking math classes.
Digi
4.3 / 5 (6) Jul 31, 2013
Ignoring the silly post from Verkle, I would like to say this was a well written interesting article and one I love to read on Phys.org - I actually learned something.
Torbjorn_Larsson_OM
2.3 / 5 (3) Jul 31, 2013
This is very interesting of course.

But I prefer Lane's & Martin's theory, especially since they show (testably and well tested) that alkaline hydrothermal vent chemistry is homologous with early chemoautotroph cellular metabolism. ["The Origin of Membrane Bioenergetics", Lane and Martin, Cell, 2012.] To that trait homology one should add the CHNOPS trait of terrestrials and cells (most common elements).

The reason I do so is because L&M don't predict extraneous chemistry coupling (serpentinization). It is a more parsimonious theory in that sense.

A nitpick would be that chemiosmosis integrates proton motive force over the membrane, so cells don't have to find motive forces larger than the largest free energy need of its cellular processes. This was likely nearly as important an evolutionary gain in early evolution as freeing a cellular compartment from its inorganic beginnings.
Torbjorn_Larsson_OM
3.7 / 5 (6) Jul 31, 2013
Creationists shouldn't troll science sites, it is hilarious and their inanities makes many deconverts from religion as seen on Dawkins's Convert's Corner.

Evolution, whether chemical or biological, is of course not "mathematically impossible" since it is, more importantly, empirically observed all the time. Nor is a physical process ever "magical", as opposed to astrology, creationism, prayers and reiki.

And no one has said evolution is a "sudden" process. On the contrary, for example it takes ~ 2 million years for us hominid apes to speciate according to the fossil record, and everyone says so. Chemical evolution started right after inflation ended in the big bang, and it took hundreds of millions of years for the first galaxies to form and spew out more complex elements than helium.
Torbjorn_Larsson_OM
2.8 / 5 (4) Jul 31, 2013
[cont]

As we now are down to the usual homologies of phylogenies between the non-living and the living, see my previous comment, the relevant math is simply maximum likelihood methods and of course hypothesis testing. Both statistic methods that undergraduates use. I can assure everyone that such math is not impossible! =D

That said, it was recently shown that activated nucleotides will be forced by free energy forces of thermodynamics to crystallize a replicating, living strand out of a random string gas under vent conditions in ~ 30 000 years. And I promise, besides the empirically observed parameters it was filled with math. (59 equations, I see.) ["Thermodynamic Basis for the Emergence of Genomes", Woo et al, PLOS Computational Biology, 2012.]

That makes abiogenesis "mathematically" possible on every habitable terrestrial that has hydrothermal vents and more than ~ 30 ky lifetime. Which is most of them. A conservative probability is ~ 1/2 of all stars or ~ 10^22 life emergences.
Torbjorn_Larsson_OM
2.8 / 5 (4) Jul 31, 2013
10^22 emergences in the observable universe. Our universe is conservatively at least 1000 times as large, hence 10^25 emergences.

Maybe I should add that the most "sudden" event studied with macroevolution methods* I know of is when B cells in our body diverge into cell lines, which can take days and weeks. Similarly for successful growth of plant hybrids.

So shortest days, for the first chemical population that evolved into a biological population tens of thousands of years at the least, for animal species millions of years at the most.

* I.e. comparable with the whole process from chemical (non-cellular chemistry) to biological (cellular chemistry) evolution.
Torbjorn_Larsson_OM
2.8 / 5 (4) Jul 31, 2013
@mBG: Ha, seems creationists have never played "20 questions", which illustrates how powerful an evolutionary process is.

Let us invert that. Our current population is ~ 10 billions or 10^10. Each will make a decision about every second (to reach for something, say), so ~ 6*10^5 decisions every day. Each day will be a unique 2^(10^(10*6*10^5)) ~ 2^(10^7) ~ 10^10^6 random outcome.

Meaning creationists thinks our daily life is about ~ 10 000 orders of magnitude as mathematically improbable and randomized than life evolving in the first place. Have I said how crazy and inane creationists are?

Well, for myself I will say my life is very probable and as ordered as I want it to be, thank you very much.
Torbjorn_Larsson_OM
2.8 / 5 (4) Jul 31, 2013
Oops, I dropped a power. It is 2^10^10^7 ~ 10^10^10^6. Daily life is ~ 10^1 000 000 oom as "random, improbable" as abiogenesis. According to creationist logic.

They don't need a creator. They need a fucking shepherd! ... oh, right.
beleg
1.2 / 5 (5) Aug 02, 2013
Understandable is defining life with physics and chemistry.
And no doubt you will eventually replicate genetics and create new genetics just with those branches of science alone.

Underlying genetics, as well as physics and chemistry, is the common denominator labeled 'information'.

Redefined life from an informational theoretical standpoint and the conditions for life no longer have constraints to exist only on earth.

Sara Walker attempted this. These are first attempts to redefine life.
You can continue to define life with physics and chemistry that lead to genetics.
That will limited your search to find life.

Or you can look at information to see where, how and what information does when you define life, death, physics, chemistry and genetics.

Once you do this you search for life stops. The origin is information.
No-cloning, no-deleting, no hiding, conserved and everywhere.
http://phys.org/n...lly.html
http://phys.org/n...ife.html

beleg
1 / 5 (1) Aug 02, 2013
last paragraph typo correction above corrected below as capitalization.
Once you do this youR search for life stops.