Saturday, September 21, 2013
Diatoms From Outerspace? How Not to Find Life on Comets
By now most of you will have seen the breathless reports that claim alien life has been found in cometary debris collected by a high altitude balloon during the Perseid meteor shower. The facts however are far more mundane.
A fragment of diatom caught in the upper atmosphere by the sampling ballooon. Image Credit University of Sheffield.
You can see the actual research the news paper reports are based on here. The summary in the conclusion of the paper is a bit less triumphal than the news reports
Despite all the images of weird looking blobs in the newspapers they have one, count it, one, fragment of a diatom (a kind of algae with hard shells, they found a bit of the shell). No alien DNA, no other evidence except this one fragment (most of the pictures in the press reports aren't even of the actual diatom fragment, but random dust particles). The authors even admit it looks like a terrestrial diatom fragment.
The authors entire argument rests on it being unlikely that chunks of diatom can last in the stratosphere for a long time.
Cometary dust, almost certain to not contain diatoms.
Except it is not that unlikely. We know that diatoms are ubiquitous in atmospheric dusts, indeed the worlds largest source of atmospheric dust is diatomaceous earth, let alone marine and other surface water droplets. Contamination of forensic and other materials with extraneous diatoms is a perennial problem. So extreme caution is need when interpreting these sorts of results.
Diatomaceous dusts can travel long distances, from the Sahara to Great Britain, and diatom containing droplets can travel far and be wafted high up.
So high that Diatoms are thought to play important roles in forming nucleation centres for rain clouds. While the authors claim there is no known mechanism for getting big dust particles that high, the very ubiquity of diatomaceous dusts, their presence at high altitude in cloud formation, and the ability of cloud air currents to loft material high into the sky make it plausible that diatom fragments could be lofted high but turbulent air currents.
Another mechanism for getting diatoms high in the air is volcanic eruptions. Despite authors claim that there were no volcanic eruptions before the balloon flight, the volcano Bata Tara in Indonesia has been exploding continuously since March, producing huge ash plumes).
Another issue relating to the contamination question is appropriate controls. While the authors had a good control for the ground based contamination of the sample cabinet, they did not do a control flight when there was no meteor shower, so we do not know if they would have picked up any diatom fragements in the absence of meteor dust.
Also, there is the question of WHY an algae that has evolved to live in marine or fresh water environments is on a comet in the first place, a frozen ball that spends most of its time far from the light of the sun is hardly the best place for things that photosynthesise in liquid water. Algae live in some very extreme environments, but spending your life frozen in a vacuum in the dark just doesn't make any sense algae wise.
The authors claims that comets have a "watery environment" is cause for head shaking, Comets are mixtures of ices (water, carbon dioxide, Carbon monoxide amongst others) which is normally frozen at the temperature below that of dry ice (frozen CO2), when the ices heat up during the comets fleeting visit to the Sun they don't go liquid, but sublimate. Hardly the best environment for a marine or river organism.
The Journal of Cosmology has form for publishing articles on life from outer space with very weak evidence. You can see my discussion of a previous paper from a different group claiming bacterial fossils in a meteorite here http://pandasthumb.org/archives/2011/03/life-from-beyon.html
Comets may have bought the building blocks of life to a primitive Earth billions of years ago, but modern diatoms living on current comets? No.
You can see the Bad Astronomers sceptical take here, and the Conversation commentary here.
You can see the actual research the news paper reports are based on here. The summary in the conclusion of the paper is a bit less triumphal than the news reports
"To conclude we note that the results presented here provide unequivocal evidence that a diatom fragment has been found in the lower stratosphere."Yes. That's the whole paper basically. "We found a diatom fragment, it's unlikely that diatom fragments can last that long in the high atmosphere, therefore it came from outer space"
Despite all the images of weird looking blobs in the newspapers they have one, count it, one, fragment of a diatom (a kind of algae with hard shells, they found a bit of the shell). No alien DNA, no other evidence except this one fragment (most of the pictures in the press reports aren't even of the actual diatom fragment, but random dust particles). The authors even admit it looks like a terrestrial diatom fragment.
The authors entire argument rests on it being unlikely that chunks of diatom can last in the stratosphere for a long time.
Except it is not that unlikely. We know that diatoms are ubiquitous in atmospheric dusts, indeed the worlds largest source of atmospheric dust is diatomaceous earth, let alone marine and other surface water droplets. Contamination of forensic and other materials with extraneous diatoms is a perennial problem. So extreme caution is need when interpreting these sorts of results.
Diatomaceous dusts can travel long distances, from the Sahara to Great Britain, and diatom containing droplets can travel far and be wafted high up.
So high that Diatoms are thought to play important roles in forming nucleation centres for rain clouds. While the authors claim there is no known mechanism for getting big dust particles that high, the very ubiquity of diatomaceous dusts, their presence at high altitude in cloud formation, and the ability of cloud air currents to loft material high into the sky make it plausible that diatom fragments could be lofted high but turbulent air currents.
Another mechanism for getting diatoms high in the air is volcanic eruptions. Despite authors claim that there were no volcanic eruptions before the balloon flight, the volcano Bata Tara in Indonesia has been exploding continuously since March, producing huge ash plumes).
Another issue relating to the contamination question is appropriate controls. While the authors had a good control for the ground based contamination of the sample cabinet, they did not do a control flight when there was no meteor shower, so we do not know if they would have picked up any diatom fragements in the absence of meteor dust.
Also, there is the question of WHY an algae that has evolved to live in marine or fresh water environments is on a comet in the first place, a frozen ball that spends most of its time far from the light of the sun is hardly the best place for things that photosynthesise in liquid water. Algae live in some very extreme environments, but spending your life frozen in a vacuum in the dark just doesn't make any sense algae wise.
The authors claims that comets have a "watery environment" is cause for head shaking, Comets are mixtures of ices (water, carbon dioxide, Carbon monoxide amongst others) which is normally frozen at the temperature below that of dry ice (frozen CO2), when the ices heat up during the comets fleeting visit to the Sun they don't go liquid, but sublimate. Hardly the best environment for a marine or river organism.
The Journal of Cosmology has form for publishing articles on life from outer space with very weak evidence. You can see my discussion of a previous paper from a different group claiming bacterial fossils in a meteorite here http://pandasthumb.org/archives/2011/03/life-from-beyon.html
Comets may have bought the building blocks of life to a primitive Earth billions of years ago, but modern diatoms living on current comets? No.
You can see the Bad Astronomers sceptical take here, and the Conversation commentary here.
Labels: comet, origin of life, scepticism
Saturday, March 12, 2011
More on Microbes and Meteorites
Over at Science in Pen and Ink Lelia Battison has an in-depth discussion of Richard Hoovers' paper on alleged "fossil" bacteria in CI1 Carbonaceous Meteorites in the Journal of Cosmology. It is an excellent article that covers a lot of issues not previously covered, and brings together some other information that has been scattered around. I'm referenced as well. Go have a read of Microbes on a Moonbeam, disentangling the Meteorite Microbe claims.
(for reference my posts on the subject are here and here)
(for reference my posts on the subject are here and here)
Labels: Meteors, origin of life, review, science
Saturday, November 28, 2009
More Evidence of Life on Mars
This mornings Australian had an article on more evidence of life existing on MArs, at least in the past. Re-examination of the Martian meteorite ALH84001 by the McKay goup suggests that the magnetite grains found in the meteorite really are of biogenic origin. The abstract of the paper is here, and it is discussed over at Spaceflight Now and Universe Today.
Personally, I think the evidence that the magnetite is from organisms is now very strong, but we still have a way to go to be fully convinced.
Personally, I think the evidence that the magnetite is from organisms is now very strong, but we still have a way to go to be fully convinced.
Labels: Mars, origin of life
Friday, January 16, 2009
Much Ado About Methane (Is there life on Mars?)
Map of Methane distribution on Mars. Image credit NASA:NASA has a headline saying "Mars is Not a Dead Planet". The reason for this headline is the discovery of appreciable amounts of Methane on Mars. What's the fuss about a gas we usually associate with bottom burps from cows? Will precisely because they are associated with bottom burps from cows, due to methane generating bacteria. Bacteria are one way the methane on Mars could have been produced, it's seasonally produced and found in special hot spots. This could be an indicator that bacteria deep in the Martian crust are churning way at whatever it is bacteria do a kilometer of so underground.
Or it could be more prosaically due to volcanic activity, but Mars is supposed to be geologically pretty inactive. Either way, the prospect that Mars is either much more geologically active than we thought, or harbouring deep seated microbes, make this red world a heck of a lot more interesting.
The NASA story is here, and more images and animations here. Emily Lakdawallah has a great post on the whole issue. Here is an article from Astrobiology Magazine, one from New Scientist and finally one from Science.
Labels: Mars, origin of life
Saturday, November 08, 2008
The Origin of Life at the Museum of Science
Aminoacyl-tRNA synthetase ribozyme, an example of the RNA-based catalysts that may have preceded protein enzymmes during the origin of life.The Museum of Science at Boston has a fantastic interactive web resource on the origins of life. Exploring Lifes Origins has a timeline of lifes evolution (with sliders), and pages on understanding the RNA world and building protocells, with a nice animation of protocell replication. The pages have been made in collaboration with ribozyme guru Jack Szostak and his laboratory, and there is a handy resources page for educators.
If you are interested in our current understanding of the origin of life, this is a very handy starting off point. You can explore ribozymes in more detail with proteopedia.
(Hat tip to Sandra Porter, biology educators should not miss her blog)
Labels: education, evolution, origin of life, prebiotic chemistry
Click to read about or order
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