How do you produce life on an early Earth bathed in ultraviolet radiation? The presumption when I was growing up was that the combination of chemicals in ancient ponds, fed energy by lightning or ultraviolet light itself, would produce everything needed to start the process. Thus Stanley Miller and Harold Urey’s experiments, beginning in 1953 at the University of Chicago, which simulated early Earth conditions to produce amino acids out of a sealed ‘atmosphere’ of water, ammonia, methane and hydrogen, with electrodes firing sparks to simulate lightning.
But there are other ways of explaining life’s origins, as a new study from the Jet Propulsion Laboratory and the Icy Worlds Team at the NASA Astrobiology Institute reminds us. Hydrothermal vents on the sea floor have been under consideration since the 1980s, with some researchers pointing to the ‘black smokers’ that produce hot, acidic fluids. The new NASA work looks at much cooler vents bubbling with alkaline solutions like those in the ‘Lost City,’ a field of hydrothermal activity in the mid-Atlantic on the seafloor mountain Atlantis Massif.
Image: This image from the floor of the Atlantic Ocean shows a collection of limestone towers known as the “Lost City.” Alkaline hydrothermal vents of this type are suggested to be the birthplace of the first living organisms on the ancient Earth. Credit: JPL.
Here there is a field of about thirty large calcium carbonate chimneys — some 30 to 60 meters tall — and a number of smaller structures venting mainly hydrogen and methane into the surrounding water. The so-called ‘water world’ theory that JPL’s Michael Russell has been working on since 1989 draws on the idea that warm alkaline vents like these would have maintained a state of imbalance with ancient oceans that were acidic. Life is, in this formulation, seen as the inevitable outcome of disequilibrium, producing enough energy to drive its formation.
Thus we have a proton gradient with hydrogen ions concentrated largely on the outside of the vent’s chimneys, which the work refers to as ‘mineral membranes.’ We also have an electrical gradient between oceans rich with carbon dioxide. and hydrogen and methane from the vents as they meet at the chimney wall. The transference of electrons could have produced complex organic compounds, using processes not so different from those that occur in mitochondria.
“Within these vents, we have a geological system that already does one aspect of what life does,” said Laurie Barge, second author of the study at JPL. “Life lives off proton gradients and the transfer of electrons.”
The work represents a fundamental shift in focus over older ‘chemical soup’ models, its examination of membrane-spanning gradients pre-empting prebiotic chemistry. The paper explains:
…there is an advantage to be gained from examining the transition from geochemistry to biochemistry from the bottom up, that is, to “look under the hood” at life’s first free energy–converting nanoengines or “mechanocatalysts.” Such an approach encourages us to see life as one of the last in a vast hierarchical cascade of emergent, disequilibria-converting entropy-generating engines in the Universe. In doing so, we keep our sights on the “astro” in astrobiology.
The researchers speculate that minerals may have played the role of enzymes in the ancient ocean, interacting with local chemicals and driving reactions. A mineral called ‘green rust’ (fougèrite) could use the proton gradient to produce phosphate-laden molecules capable of storing energy. Molybdenum is also in play, a rare metal that can drive important chemical reactions. Thus basic metabolic reactions around sea floor hot springs may help to explain not only how life emerged on our own planet but also how it may emerge on worlds far beyond.
On this latter point, the paper explains how to proceed:
In considering habitability and the potential for life elsewhere in the Solar System and beyond, the physical and chemical disequilibria that obtain on wet icy rocky worlds, and the various processes that might relieve them, need to be established. If life’s origin is ultimately coupled to geophysical convection in a particular geochemical context, one should be able to make predictions about life’s likelihood on a planet or moon of interest from application of coupled chemical and fluid/geodynamical modeling, and from the availability of key feedstocks, thus accounting for other planetary energetic drivers, for example, tidal and radiogenic heating, solar wind interactions, magnetic dynamos—appropriate to the object in question.
We’d like to account, in other words, for the disequilibrium-producing factors that could play an astrobiological role on multitudes of exoplanets. The possibilities range widely, from gravitational effects to thermal and chemical gradients that can all play a role in life’s inception. Particularly close to home, of course, we focus in on places like Enceladus and Europa, where we have nearby laboratories for observing these processes in action. Until we can put the right kind of instrumentation on the scene, continuing Earth-bound lab work on these ideas is the way forward.
The paper is Russell et al., “The Drive to Life on Wet and Icy Worlds,” Astrobiology Vol. 14, Issue 4 (April 15, 2014). Available online. A JPL news release is also available.
A very thought provoking article about a field of research that I wish I understood better. Thanks Paul.
This article supports some notions I’ve had about the origin of life.
The phosphate bond of an RNA polymer is rather unstable and is easily hydrolyzes under heat, UV or changes in pH.
If you have RNA monomers in an acidic ocean and the they enter an area of more neutral pH with the right substrate, then chains of them could begin to form, presumably this would be in the chambers and fissures in the rocks feeding water into the alkali vents. You would also need to assume the RNA chains could circulate in this collegial environment for some time before being vented back into the acidic ocean, which would de-polymerize them.
If this arrangement was a laboratory experiment, you would have a vessel in which a trickle of RNA monomers are introduced, then gently circulated over a polymerizing substrate that could allow the polymers could break free and circulate, then the continuous removal of a small portion of the contents, which would be broken down into monomers to be fed back into the reaction vessel.
The resulting chains of RNA would be randomly arranged, but if under these circumstance an arrangement that could self-replicate arose by random chance, it would start replicating while circulating and, even though there would be continuous loss of the replicating chains, they would come to predominate and eventually you would have nothing but self replicating polymers.
What you would have is a natural set-up that selects for self-replication.
There is some evidence to indicate that you can get self-replicating RNA chains at about 50 base pairs long. The random chance of the right arrangement occurring is about 1 in 4 to the power of 50, which is a very large number, but given enough time this process would hit on it.
Robert Hazen covers the basis of this theory as a chapter in his book gen*e*sis: The Scientific Quest for Life’s Origins(2005). This paper nicely fleshes it out. It has also been suggested that cell-sized pockets in rocks could have been the template for lipid cell membranes to form, containing the metabolic system. What is interesting is that the article is suggesting metabolism came first, then replication, rather than replication (RNA world) and then metabolism.
@Dave Moore – there have been many experiments trying to make RNA polymerize without much success. Recently there was much interest in a “proto-RNA” that would polymerize well in water. This was considered a breakthrough. It doesn’t require alkaline conditions AFAICS.
Here is a nice overview of the metabolism first vs replication first theories. Note the implications for life elsewhere – metabolism first suggests life is ubiquitous, whereas replication first suggests it might be rare. Of course this changes depending on experiments that show that replicating molecules might be more easily formed that erstwhile thought.
I wonder where these creatures’ ancestors were living before South America and Africa split, opening up the Atlantic? Did they have much trouble migrating in? Were they living in subterranean biomes?
17 April 2014 Last updated at 21:54 ET
Ancient plants ‘frozen in time’ by space impacts
By Paul Rincon
Science editor, BBC News website
Ancient plant material has been preserved in the glass formed by asteroids hitting the Earth, scientists report.
The “frozen in aspic” appearance of what are apparently fragments of grass is spectacular enough.
But a team writing in Geology journal says that delicate organic chemicals have also been conserved inside.
Incredibly, the searing heat generated by the impacts was responsible for the remarkable preservation.
It turns out the composition of the plant material is very similar to the composition of the impact glass itself.”
The findings could even point to a new way of searching for past life on Mars.
stephen; the oceans have opened and closed many times since the origin of life on this planet, so life has had to migrate into new oceans on several occasions. Life can migrate much more rapidly than oceans can form, in any case.
The implications for the speed at which we can solve the mystery of the first stages of life are discussed here:
A collection of links to the July 14, 2014 meeting on astrobiology by NASA at their headquarters in Washington, D.C.
They appear to have used this meeting to give SLS yet another reason to exist. NASA must be desperate to find a mission for their big rocket plan if they have to resort to finding alien life as a promotion to make this booster a reality.
Astrobiology is the redheaded stepchild of NASA (is that still PC to say?), great for exciting the general public into thinking that is what it does – look for aliens – but otherwise confined to the back rooms. And in the early 1990s, its SETI program was scrapped by Congress and for a while after both astrobiology and SETI were dirty words at NASA, let us not forget this.
The last link above contains a video of the conference in its comments section, FYI.
September 29, 2014
Resurrecting 4-Billion-Year-Old Proteins to Decode Earth’s Early Epochs –“Will Aid Our Search for Life in the Universe”
Thanks to advances in a niche field called paleobiochemistry, researchers in the last decade have started to “resurrect” ancient proteins. Studying these proteins’ properties is offering us glimpses of what life was like in bygone epochs.
“Although the majority of resurrection studies currently focus on resurrecting one or two protein families at a time,” says Eric Gaucher, a pioneering paleobiochemist and a professor biology at Georgia Tech. “we anticipate that we will be able to resurrect a complete ancestral genome in the near future and jump-start this genome using modern life to, in essence, resurrect long extinct forms of life.”
The results so far are compelling. Take, for example, beta lactamase proteins, which first evolved between 2 to 3 billion years ago. These ancient proteins actually remain more stable and work better in hot spring-like temperatures of between 130 and 150 degrees Fahrenheit (54 and 66 degrees Celsius) compared to their modern counterparts.
Other proteins, called thioredoxins, originated 4 billion years ago at the time of life’s origin, and these ancient proteins stay active in acidities that would break down many modern proteins. Findings of this sort help paint a portrait of life prior to 500 million years ago in the vast era known as the Precambrian.
“Molecular resurrection studies provide a new line of evidence supporting geological models that suggest that the Precambrian Earth hosted a hotter and more acidic ocean than its modern counterpart,” siad Gaucher. “Early life was adapted to this environment.”
Paleobiochemistry should have much more to eventually say on this topic. Toward this end, Gaucher and colleagues at the University of Granada in Spain have a new paper in the June 2014 issue of the scientific journal Proteins: Structure, Function, and Bioinformatics. The study compares two common techniques used in paleobiochemistry that have potential biotechnology applications, such as finding ways of dealing with the scourge of antibiotic resistance. The two methods allow scientists to extrapolate the composition of proteins from eons ago.
Deciphering the development of biota on Earth is important not only for piecing together our planet’s past — and thus its potential future — but also for gauging where else life might arise in the cosmos.
“Knowing how life originated and diversified on early Earth provides us with a perspective on the conditions that support primitive life,” said Gaucher. “This information can better inform our decisions to search for life on other planets.”
Full article here:
Better yet than toying with individual proteins, though, would be sizing up a whole organism. And stay tuned: by building on their success with phylogenetics, Gaucher and colleagues hope to be able to bring ancient bacteria and archaea back from the dead.
“Although the majority of resurrection studies currently focus on resurrecting one or two protein families at a time,” Gaucher said, “we anticipate that we will be able to resurrect a complete ancestral genome in the near future and jump-start this genome using modern life to, in essence, resurrect long extinct forms of life.”