#17! The question posed by a reader was just too good not to include the series.
What's the current take on a deep-sea origin of life? I just finished reading Genesis by Robert Hazen where he discusses some of the hypothesis' pros and cons and how there is something of a divide between the "ventists" and the "Millerites" and was wondering if deep-sea scientists naturally fell into the "ventist" camp.
First some background, in Origin of Life Circles you can either be a Ventist or Millerite. Millerites are disciples of Stanley Miller, who created an early earth analog in the laboratory that produced organic molecules from water, methane, ammonia, hydrogen, and shot of electricity. Miller and Urey's experiments in 1952, although quite distant from demonstrating how life evolved, pointed to the possibility that the conditions on the young earth's surface could produce the basic building blocks of life. They operate under the Oparin-Haldane hypothesis or the organic soup (or primordial ooze) hypothesis. The problem is that the early atmosphere would have to be reducing for these reactions to work. Recent evidence suggests this may not be the case. As well, some argue that CO2 and/or CO would reduce organic material by chemosynthesis. So if the earth as a whole was not reducing, then you would need particular evironments to be.
Fast forward to the 1970's and the discovery of hydrothermal vents, a reducing envrionment, which spawns a new line of thinking. The interface of cold and hot waters allow for unique reactions to occur. Moreover, the extreme pressure, protection from UV radiation, abundant geothermal energy, and both methane and sulfide provide the necessary conditions to serve as a cradle of life in the deep depths of the ocean.
But to be a ventist is blasphemy, guilty of desertion of the very principles of Miller and Urey!
Of this group is Robert Hazen publisher of 19 books, concert trumpist, professor, cyrstallographer, etc. Hazen claims, "Miller and his scientific cohort had staked their claim to a surface origin of life, and they seemed determined to systematically head off dissenting opinions." The Millerites attack the theory that life could have begun at ocean vents, saying high temperatures would have destroyed amino acids. Van Dover in her book on vents, points to both empirical and laboratory evidence indicating this is not the case. Van Dover also present an excellent figure of phylogentic tree of Bacteria, Eucarya, and Archaea, that point to the hyperthermophilic nature of the basal taxa.
Add to this a recent study from Geology that types of clay mineral can convert simple carbon molecules to complex ones in conditions similar to the hot and wet environment of hydrothermal vents. The group simulated a vent in the laboratory by immersing various types of clay in pressurized water at 300 °C for several weeks and looking at the fate of methanol, a compound formed readily formed at vents. Having helped such delicate molecules to form, the clays can also protect them from getting broken down in the piping hot water issuing from the vents." Not to mention the ultimate buffering from meterorite impacts that occurred on the early earth.
On the other hand. Miller, himself, called the vent hypothesis "a real loser." "This whole hype on hydrothermal systems and everything is just bogus," says Jeff Bada, professor of marine chemistry at Scripps and the most prominent protégé of Miller. "I think he oversells this." Bada questions an experiment that Hazen and his colleagues conducted in which they managed, in mimicking deep-sea pressures and temperatures, to create an important biomolecule called pyruvate: "I have some strong questions about whether that experiment is even valid. We haven't been able to repeat it." Hazen says, "Ultimately the truth comes out."
Quotes via Achenbach's article in the Washington Post
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Are you up on pyrrhite chimneys?
God, not Bada again. He doesn't represent anything about the community except for the Miller - Bada - Lazcano tripe that they endlessly push in popular articles and the occasional pompous review. Urey had some different opinions, polymath that he was. Not to mention, at the time of the original experiments in the late 50's, nobody even knew of such a thing as a vent. It's ridiculous to pretend they pro-actively negated any related hypotheses.
The fact remains that there a million ways to make an enormous variety of organics, whether you go the Miller-Urey route, the simulated vent route, or a hundred pathways in between. Making organics is no big deal. Stability and persistence are the larger issue. And, any way you slice it, Bada needs to button it and stop getting in the way of people's ability to do research and explore new avenues. You would think it was blasphemy of the worst order not to agree with him. Bada's experiments have consisted primarily of heating some arbitrary solutions in pyrex. Apparently the last word, you know.
Right now the cutting edge stuff is all coming out of Japan, and a lot of it in now in English. Do have a look if you are serious about the field. Also, your statements about 'Miller' people and 'vent' people completely neglect the iron-sulfur hypothesis, on which there is a lot of good work.
Ironically, I believe I just saw a multiple-author review in Science just this month, with both Bada and Hazen on it. Strange bedfellows? Hazen's book was not bad, if simplistic and a bit melodramatic at times.
If life originated at vents, where did oxygen come from in the seawater? The microbes need oxygen for chemoautotrophy. Current theory seems to point to photosynthetic microbes saturating the early oceans and atmosphere with oxygen. Is there any evidence that the (deep) oceans were oxygenated prior to the arrival of photosynthetic microbes? I don't know of any off the top of my head...
Or perhaps anaerobic oxidation of reduced chemicals gave rise to microbes who could utilize oxygen once it became available over time as photosynthesis produced more oxygen and currents had enough time to mix the oxygen around the global oceans.
"Abundant UV" - where would this come from so deep below the surface? Surely not the Sun.
Kevin,
Probably the latter and to David UV from the thermal radiation of the vent.
Craig - any thoughts concerning how life migrated away from the vents given the major environmental conditions this would entail? Or would a self-contained, auto-catalytic proto-life not really "care" about these changes as much as an evolved organism?
Jim,
Not quite sure about the process of evolving away from the vent. Will have to do some more research.
anonchemist,
I am sorry you misinterpreted the post. I meant to have some fun talking about the two camps.
I enjoyed this post, thank you. May I suggest changing the "Live" in the title to "Life". I don't know if it was typo or not and I'm not from the spelling or grammar police -- I make more than enough of my own. I actually read it as "Life" and didn't notice it until I was creating a link here at my blog. This post is more likely to be picked up on a google search with "womb of life" and it deserves to be read by more people!
Thanks for the heads up! A busy week and the error in the title slipped through.
CR McClain: UV radiation.
I checked some numbers.
1: thermal radiation from the vent. No. Vent temperature is aboout 750 degrees max. Significant UV radiation doesn't start until about 5000. At least. (F vs C irrelevant for that much difference).
2: UV penetration from surface insolation. Again, no. UV energy is down to 1% at 25m depth. Vents are considerably deeper than that.
So the UV comment must have been a typo. At most there's minor IR flux, not enough to drive mutative chemical processes. Maybe better to just drop the reference altogether - the other factors are xtreme enough.
So I am now interested in the migration path from reducing vent environment to oxidizing surface environment. If.
David,
Thanks for catching the typo. I lost some text apparently in the transfer over to moveable type. It should have read protection from UV and abundant geothermal energy.
It would be very interesting to see if at shallow vents you find a consortia of microbes utilizing photosynthetic energy and reduced chemical energy.
It may be reasonable that vents were shallower in the past and the microbes evolved with the depth decrease of vents until they were no longer able to utilize photosynthetic energy and relied fully on reduced chemicals or metals.
In the sediments around seeps you see microbial consortia (and in the guts of termites!) that supply each other with the chemicals needed for energy. See Boetius et al. 2000 (Nature 407: 623-626) for a seep example http://www.nature.com/nature/journal/v407/n6804/abs/407623a0.html
and Raghoebarsing et al. 2006 (Nature 440: 918-921) http://www.nature.com/nature/journal/v440/n7086/abs/nature04617.html
for an agricultural example.