Study tests theory that life originated at deep sea vents

Apr 09, 2014
Clear hot spring fluids spew from a talc structure at the Von Damm vent field, a mile and a half beneath the Caribbean Sea. The researchers show that fluids emanating from Von Damm and other hot spring areas around the global mid-ocean ridge system contain a sulfur compound, methanethiol, that is indicative of pyrolysed subsurface life. The red laser dots are 10cm apart, for scale. Photograph courtesy of the Little Hercules ROV, NOAA Okeanos Explorer Program, Mid-Cayman Rise Expedition 2011. Credit: Woods Hole Oceanographic Institution

One of the greatest mysteries facing humans is how life originated on Earth. Scientists have determined approximately when life began (roughly 3.8 billion years ago), but there is still intense debate about exactly how life began. One possibility - that simple metabolic reactions emerged near ancient seafloor hot springs, enabling the leap from a non-living to a living world – has grown in popularity in the last two decades.

Recent research by geochemists Eoghan Reeves, Jeff Seewald, and Jill McDermott at Woods Hole Oceanographic Institution (WHOI) is the first to test a fundamental assumption of this 'metabolism first' hypothesis, and finds that it may not have been as easy as previously assumed. Instead, their findings could provide a focus for the search for on other planets. The work is published in Proceedings of the National Academy of Science.

In 1977, scientists discovered biological communities unexpectedly living around seafloor hydrothermal vents, far from sunlight and thriving on a chemical soup rich in hydrogen, carbon dioxide, and sulfur, spewing from the geysers. Inspired by these findings, scientists later proposed that hydrothermal vents provided an ideal environment with all the ingredients needed for microbial life to emerge on early Earth. A central figure in this hypothesis is a simple sulfur-containing carbon compound called "methanethiol" - a supposed geologic precursor of the Acetyl-CoA enzyme present in many organisms, including humans. Scientists suspected methanethiol could have been the "starter dough" from which all life emerged.

The question Reeves and his colleagues set out to test was whether methanethiol—a critical precursor of life – could form at modern day vent sites by purely chemical means without the involvement of life. Could methanethiol be the bridge between a chemical, non-living world and the first microbial life on the planet?

Carbon dioxide, hydrogen and sulfide are the common ingredients present in hydrothermal black smoker fluids. "The thought was that making methanethiol from these basic ingredients at seafloor hydrothermal vents should therefore have been an easy process," adds Reeves.

To collect their samples, the researchers went to hydrothermal vent sites where the chemistry predicted they would find abundant methanethiol, and others where very little was predicted to form. In total, they measured the distribution of methanethiol in 38 hydrothermal fluids from multiple differing geologic environments including systems along the Mid-Atlantic Ridge, Guaymas Basin, the East Pacific Rise, and the Mid-Cayman Rise – an unprecedented survey - over a period between 2008 and 2012. Credit: Meg Tivey, Woods Hole Oceanographic Institution

The theory was appealing, and solved many of the basic problems with existing ideas that life may have been carried to Earth on a comet or asteroid; or that genetic material emerged first – the "RNA World" hypothesis. However, says Reeves, "it's taken us a while to get out there and actually start to test this 'metabolism first' idea in the natural environment, by using modern vents as analogs for those that were around when life first began."

And when they did get out there, the scientists were surprised by what they found.

To directly measure methanethiol, the researchers went to sites where the chemistry predicted they would find abundant methanethiol, and others where very little was predicted to form. In total, they measured the distribution of methanethiol in 38 from multiple differing geologic environments including systems along the Mid-Atlantic Ridge, Guaymas Basin, the East Pacific Rise, and the Mid-Cayman Rise over a period between 2008 and 2012.

"Some systems are very rich in hydrogen, and when you have a lot of hydrogen it should, in theory, be very easy to make a lot of methanethiol," says Reeves. The fluids were collected in isobaric gas-tight samplers (IGTs) developed by Jeffrey Seewald, which maintain fluids at their natural pressure and allow for dissolved gas analyses.

Instead of an abundance of methanethiol, the data they collected in the hydrogen-rich environments showed very little was present. "We actually found that it doesn't matter how much hydrogen you have in black smoker fluids, you don't seem to be making a lot of methanethiol where you should be making a lot of it," Reeves says. Surprisingly, in the low-hydrogen environments, where much less should form, the research actually found more methanethiol than they had predicted, contradicting the original idea of how methanethiol forms. Overall, this means that jump-starting proto-metabolic reactions in hydrogen-rich early Earth hydrothermal systems through carbon-sulfur chemistry would likely have been much harder than many had assumed.

Critically, the researchers found an abundance of methanethiol being formed in low temperature fluids (below about 200°C), where hot black smoker fluid mixes with colder sea water beneath the seafloor. The presence of other telltale markers in these fluids, such as ammonia – a byproduct of biomass breakdown – strongly suggests these fluids are 'cooking' existing microbial organic matter. The breakdown of existing subseafloor life when conditions get too hot may therefore be responsible for producing large amounts of methanethiol.

"What we essentially found in our survey is that we don't think methanethiol is forming by purely chemical means without the involvement of life. This might be disappointing news for anyone assuming an easy start for hydrothermal proto-metabolism," says Reeves. "However, our finding that methanethiol may be readily forming as a breakdown product of provides further indication that life is present and widespread below the seafloor and is very exciting."

The researchers believe this new understanding could change how we think about searching for life on other planets. "The upside is, now we have a pretty simple marker for life. Someday if we can land a rover on the ice-covered oceans of Jupiter's moon Europa – another place in the Solar System that may host hydrothermal vents, and possibly life – and successfully drill through the ice, the first thing it should probably try to measure is methanethiol," Reeves says. "This is already something scientists are thinking about, and it is exciting to think this might even happen in our life time."

As for the search for the origins of life, Reeves agrees that hydrothermal vents are still a very favorable place for life to emerge, but, he says, "maybe methanethiol just wasn't a good starter dough. The hydrothermal environment is still a perfect place to support early life, and the question of how it all started is still open."

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RealScience
5 / 5 (2) Apr 09, 2014
It would have been good if they had check alkaline hydrothermal vents (white smokers) as well, as these have been favored over black smokers for many years now for life's origins.
Torbjorn_Larsson_OM
5 / 5 (1) Apr 10, 2014
Nice to see testing of the serpentinization/fuel cell theories of life!

The article is somewhat confusing though, since it mentions black smokers but then the sample map (as well as the abstract http://www.pnas.o...4e7550ba ) mentions vents of all kinds, including the serpentinization (ultramafic) white smokers that are the (Hadean, so CO2 fed) chemical factories considered.
Torbjorn_Larsson_OM
5 / 5 (1) Apr 10, 2014
[ctd]

Seeing the datings, the 2008-2012 research seems to rely on the Martin & Russell 2007 paper http://rstb.royal...887.long : "A model for the origin of biochemistry at an alkaline hydrothermal vent has been developed that focuses on the acetyl-CoA (Wood–Ljungdahl) pathway of CO2 fixation [...] when sulphur is included in thermodynamic simulations of H2/CO2 equilibria in hydrothermal systems, the results indicate that millimolar—or even greater—concentrations of methyl sulphide (CH3SH, methanethiol) are expected in hydrothermal fluid (Schulte & Rogers 2004). "

[tbctd]
Torbjorn_Larsson_OM
5 / 5 (1) Apr 10, 2014
[ctd]

That pathway was (for phylogenetic reasons) succeeded by the 2013 merged pathway of Nitschke & Russell, perhaps also having foreknowledge of the 2008-2012 data: "we propose that a variant of modern methanotrophy is more likely than traditional WL systems to date back to the origin of life. The proposed model furthermore better fits basic thermodynamic demands and palaeogeochemical conditions suggested by recent results from extant alkaline hydrothermal seeps." [ http://rstb.royal...20120258 ] (Unfortunately I have no access to it right now, so can't see if the thiols are indeed replaced by other metabolites.
Torbjorn_Larsson_OM
5 / 5 (1) Apr 10, 2014
Now I've checked the old vs new vent theory WL pathways.

The former pathway indeed contains a sulphide pathway, but starting as a supplement to the serpentinization process reduction of CO (vent/ocean vs deep vent localized). Then there is a WL need for a HSCoA prerunner. which is proposed to be a simpler thiol ending up as acetyl thioester. [Ibid.]

The new UCA pathway, which was suggested from phylogeny, keeps the latter CoA dependence. However, and crucially, there doesn't seem to be an initial need for a CoA analog to make the acetyl. It can derive from an inorganic compartment barrier, where NiFe sites do the ACS type reaction (where later CoA becomes involved). So no initial need for organic sulfur.
Torbjorn_Larsson_OM
5 / 5 (1) Apr 10, 2014
There may be a bootstrap involved (unless the breakdown of existing life presumes thiols). Meaning that life may have been responsible for introducing the breakdown pathway that captured sulfur into organic compounds, making thiols available for initial use.
georgi_gladyshev
1 / 5 (1) Apr 29, 2014
Dear Colleagues,
I am sending you the information on new my hierarchical thermodynamic idea about the origin of abiogenic and simple living structures, for example, nanobes....
It can be argued that in the evolution of the water local cycles on the young Earth due to chemical and supramolecular transformations of trace contaminants were formed liquid- crystal hierarchical structures. These structures during many water cycles step by step were turned into abiogenic, and later into "simple living structures." Individual unstable molecules (eg , purines ) were preserved due to the action of "the principle of substance stability". This principle prevented the breakdown of fragments of these molecules in short chains of nucleic acids. In other words, these unstable molecules (their fragments) were protected as a result of action of relatively strong hydrogen bonds between nucleobases. It can be assumed that the initial stages of such cyclic processes of origin of life we can also see now, in their initial stages. ... http://endeav.net...ure.html]http://endeav.net...ure.html[/url]]http://endeav.net...ure.html[/url]
Sincerely,
Georgi Gladyshev
Professor of Physical Chemistry

Addition
Dear Colleagues,
I am sending you the information about thermodynamics of origin of life and evolution. Have a look at, please.
Thank you!
Sincerely,
Georgi Gladyshev
Professor of Physical Chemistry

Life arises and exists where there are the appropriate conditions of the environment and the cyclic exchange of matter and energy. http://endeav.net...ure.html]http://endeav.net...ure.html[/url]]http://endeav.net...ure.html[/url]
During the formation of the most thermodynamically stable supramolecular structures in evolution, in accordance with the second law, Nature spontaneously uses predominantly the least thermodynamically stable molecules. http://gladysheve...ess.com/article/on-the-principle-of-substance-stability/]http://gladysheve...ability/[/url]
Life: The simplest forms of life can occur in the water cycle on the planet. http://endeav.net...ure.html]http://endeav.net...ure.html[/url]]http://endeav.net...ure.html[/url]

The origin of life can be understood on the foundations of hierarchical thermodynamics without representations about dissipative structures and any fantastic ideas. Hierarchical thermodynamics was created on the foundation of the theory of Gibbs - the most rigorous physical theory.
Nature seeks to the minimum values of the specific Gibbs function (to the specific free energy) of formation of supramolecular structures. The same we can say also about the interactions between atoms.
One can also say that these structures are looking for stability.
This statement corresponds to the familiar doctrine that nature to strive for the densest packing of interacting supramolecular structures. In other words, nature tends to "the maximum satisfaction." It is looking for a maximum matching of "the key to the lock." We see this situation at the crystallization and the recrystallization of minerals, biological crystals and liquid crystal structures. Biological structures are improved in ontogeny, phylogeny and evolution. The structure of catalytic systems also is improved, which leads to acceleration of biological processes in the evolution. Finding of appropriate structures in nature is associated with cyclical changes of environmental parameters. http://gladysheve...ess.com/article/thermodynamics-of-origin-of-life/]http://gladysheve...of-life/[/url]
http://www.mdpi.o...0098.pdf]http://www.mdpi.o...0098.pdf[/url]]http://www.mdpi.o...0098.pdf[/url] Aging

As part of its applicability thermodynamics explains everything that happens in the world.
To understand the origin of life, its evolution and aging we should use the hierarchical thermodynamics and principle of substance stability (1977). http://www.mdpi.o...0098.pdf]http://www.mdpi.o...0098.pdf[/url]]http://www.mdpi.o...0098.pdf[/url]
Life: The principle of substance stability establishes the common life code in the universe http://endeav.net...ife.html
The origin of life can be explained through the study of thermodynamics of universe evolution http://gladysheve...ess.com/
Origin of Life (Abiogenesis) - Darwin's selection: the survival of stable supramolecular structures.
Why does life originate and exist now? Origin of life and its evolution are the result of action of laws of hierarchical thermodynamics and the principle of substance stability. The criterion of evolution of living system is the change (during evolution) of the specific free energy (Gibbs function, G) of this living system formation. http://endeav.net/news.html
The hierarchical thermodynamics has predicted the observed effects many years ago. About the phenomenon of life has been written in many articles and some monographs (for example, see: Gladyshev Georgi P. Thermodynamics Theory of the Evolution of Living Beings.- Commack, New York: Nova Science Publishers, Inc.- 1997.- 142 P., Thermodynamics optimizes the physiology of life http://ru.scribd....-11-2011 , Int. J. Mol. Sci. 2006, 7, 98-110 http://www.mdpi.o...0098.pdf]http://www.mdpi.o...0098.pdf[/url]]http://www.mdpi.o...0098.pdf[/url] , Site in English:
Hierarchical thermodynamics solves the puzzle of life. The role of catalysis
http://gladysheve...ess.com/article/hierarchical-thermodynamics-solves-the-puzzle-of-life/ http://gladysheve...ess.com/article/thermodynamics-of-origin-of-life/]http://gladysheve...of-life/[/url]
http://creatacad....;lng=eng http://creatacad....;lng=eng , http://www.eoht.i...raphy%29 http://www.statem...ladyshev )!
Thermodynamic evolution http://www.statem...volution
georgi_gladyshev
not rated yet May 03, 2014
Life as a defending process

Abiotic development and primary life evolved on the young Earth (or on the celestial bodies). These processes are still produced today. However, the existing life protects itself and prevents the development of own primary forms. This is the self-defending property of life. Origin, development and the preservation of life is controlled by the hierarchical thermodynamics of complex systems.
http://endeav.net...ife.html