Lecture of the Week: Part II: Could We Tell Life If We Saw It?
Wirt Atmar
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Part II: Could We Tell Life If We Saw It?
Potential for Early Life Hosted
in Basaltic Glass on a Wet Mars
Neil R. Banerjee
University of Alberta, University of Bergen, Norway
11 min. (requires QCShow Player)
Can we recognize the hallmarks of life if we see it, even if it is of
a completely different biochemistry than anything we currently know?
This is the question that will pervade our coming search for life in
the universe.
We believe that the answer is yes, simply because we expect the
physics of the Darwinian evolutionary process to be universal. Life
inherently builds complex and highly refined structures. Andy Knoll of
Harvard has said that a good biomarker should be something that is
difficult to accomplish through inorganic processes. And Norm Horowitz
of CalTech said much earlier, in 1956, that a good biomarker should
display the fingerprint of natural selection.
Joe Kirschvink, in the previous lecture, emphasized the extraordinary
quality of the magnetite crystals found in the Martian meteorite
ALH84001, levels virtually impossible to achieve by inorganic means.
This week's lecture is similar, but celebrates a completely different
phenomenon: the etchings made by bacteria feeding on glass.
It wasn't until the early 1990's that the etchings in medieval church
windows in Europe were first recognized to be caused by bacteria. That
finding was almost immediately extended to natural basaltic glasses as
well, where the same patterns were quickly discovered.
In this short but compelling talk given by Neil Banerjee to The Second
Conference on Early Mars in October, 2004, Neil describes the
bacterial process in both modern and very ancient terrestrial rocks.
Evidence for early life on Earth has proven to be similarly
controversial. Neil and his co-authors have recently discovered
indicators of early life in the formerly glassy rims of ~3500 million
year-old basaltic pillow lavas, essentially indistinguishable from
those found in modern rocks. These ancient volcanic glasses represent
a previously unexplored setting in the search for early life on Earth.
If this environment is true for Earth, it may well be true for Mars as
well. The cratered surface of Mars likely hosts countless glassy
basaltic impact breccias that may have been submerged in water for
extended periods of time. Such rocks may well represent a viable
habitat for early life on Mars, and Neil recommended at the end of his
talk that such rocks be seriously considered for a future sample
return mission.
As it occurs, that sample return mission may already have been
accomplished — a century ago, in 1911, at Nakhla, Egypt.
In an article published this week in the journal Astrobiology, Martin
Fisk and co-authors argue that a new study of the Nakhla Martian
meteorite has revealed a series of microscopic tunnels that are
similar in size, shape and distribution to tracks left on Earth rocks
by feeding bacteria (see image at left).
Fisk, a professor of marine geology in the College of Oceanic and
Atmospheric Sciences at Oregon State University and lead author of the
study, said the discovery of the tiny burrows do not confirm that
there is life on Mars. "Virtually all of the tunnel marks on Earth
rocks that we have examined were the result of bacterial invasion,"
Fisk said. "There are two possible explanations," he added. "One is
that there is an abiotic way to create those tunnels in rock on Earth,
and we just haven't found it yet. The second possibility is that the
tunnels on Martian rocks are indeed biological in nature."
The igneous rock fragment from Nakhla — which weighs about 20 pounds —
is 1.3 billion years in age. It is believed that the rock was exposed
to water about 600 million years ago, based on the age of clay found
inside the rocks. "It is commonly believed that water is a necessary
ingredient for life," Fisk said, "so if bacteria laid down the tunnels
in the rock when the rock was wet, they may have died 600 million
years ago."
"Several types of bacteria are capable of using the chemical energy of
rocks as a food source," he said. "One group of bacteria in particular
is capable of getting all of its energy from chemicals alone, and one
of the elements they use is iron – which typically comprises 5 to 10
percent of volcanic rock."
The igneous rocks from Mars are similar to many of those found on
Earth, and virtually identical to those found in a handful of
environments, including a volcanic field found in Canada. Although the
tracks in the Nakhla meteorite do not appear to be as complex as they
are in Neil Banerjee's terrestrial basaltic glasses, they are
nonetheless strikingly similar.
=====================================
Perplexed in Peoria
"Wirt Atmar" <at...@aics-research.com> wrote in message news:e09btv$2gnb$1...@darwin.ediacara.org...
>
> Potential for Early Life Hosted
> in Basaltic Glass on a Wet Mars
> Neil R. Banerjee
> University of Alberta, University of Bergen, Norway
> 11 min. (requires QCShow Player)
>
> quality of the magnetite crystals found in the Martian meteorite
> ALH84001, levels virtually impossible to achieve by inorganic means.
> This week's lecture is similar, but celebrates a completely different
> phenomenon: the etchings made by bacteria feeding on glass.
>
> It wasn't until the early 1990's that the etchings in medieval church
> windows in Europe were first recognized to be caused by bacteria. That
> finding was almost immediately extended to natural basaltic glasses as
> well, where the same patterns were quickly discovered.
>
> In this short but compelling talk given by Neil Banerjee to The Second
> Conference on Early Mars in October, 2004, Neil describes the
> bacterial process in both modern and very ancient terrestrial rocks.
> Evidence for early life on Earth has proven to be similarly
> controversial. Neil and his co-authors have recently discovered
> indicators of early life in the formerly glassy rims of ~3500 million
> year-old basaltic pillow lavas, essentially indistinguishable from
> those found in modern rocks. These ancient volcanic glasses represent
> a previously unexplored setting in the search for early life on Earth.
> "Several types of bacteria are capable of using the chemical energy of
> rocks as a food source," he said. "One group of bacteria in particular
> is capable of getting all of its energy from chemicals alone, and one
> of the elements they use is iron – which typically comprises 5 to 10
> percent of volcanic rock."
These glass-eating, or glass tunneling, microbes are fascinating, but
where does their energy come from? Presumably they are chemolithoautotrophs.
By definition, glasses are higher in energy than crystals of the same
composition. And presumably there may be some decrease in energy due
to simply dissolving the glass and releasing the more soluble ions into
solution. But it doesn't seem easy to turn this kind of diffuse energy
supply into phosphate bonds for organism growth and maintenance. To
do that it would seem that you need redox chemistry. So what element
is being oxidized so that carbon can be reduced?
Laboratory glassware is not generally soluble in acids. I wonder whether
basaltic glasses are more susceptible. I do note that an organism
living in a tunnel and exporting protons to the face of the tunnel can
probably generate an extremely low pH. But it takes energy to export
those protons. Where does the energy come from? Not from turning Fe++
to Fe+++, I think. Something else must be being oxidized and then
released to solution. Sulfur? Phosphides? There are some trace
metals like Mo and Cr that might be oxidized to a soluble form, but
I would be surprised if the microbes could find enough of them to
pay the expense of mining for them. Does anyone have a link to info
on the overall metabolic scheme for these microbes?
Tom Hendricks
> Evidence for early life on Earth has proven to be similarly
> controversial. Neil and his co-authors have recently discovered
> indicators of early life in the formerly glassy rims of ~3500 million
> year-old basaltic pillow lavas, essentially indistinguishable from
> those found in modern rocks. These ancient volcanic glasses represent
> a previously unexplored setting in the search for early life on Earth.
This is the part that caught my eye. Does anyone know more
about this study? An abstract on the net perhaps?
The 3,500 million period for life is very controversial.
I'd like to see his 'recently discovered' take on it.
Tom Hendricks
> Evidence for early life on Earth has proven to be similarly
> controversial. Neil and his co-authors have recently discovered
> indicators of early life in the formerly glassy rims of ~3500 million
> year-old basaltic pillow lavas, essentially indistinguishable from
> those found in modern rocks. These ancient volcanic glasses represent
> a previously unexplored setting in the search for early life on Earth.
This is the part that caught my eye. Does anyone know more
Wirt Atmar
> These glass-eating, or glass tunneling, microbes are fascinating, but
> where does their energy come from? Presumably they are chemolithoautotrophs.
> By definition, glasses are higher in energy than crystals of the same
> composition. And presumably there may be some decrease in energy due
> to simply dissolving the glass and releasing the more soluble ions into
> solution. But it doesn't seem easy to turn this kind of diffuse energy
> supply into phosphate bonds for organism growth and maintenance. To
> do that it would seem that you need redox chemistry. So what element
> is being oxidized so that carbon can be reduced?
>
> Laboratory glassware is not generally soluble in acids. I wonder whether
> basaltic glasses are more susceptible. I do note that an organism
> living in a tunnel and exporting protons to the face of the tunnel can
> probably generate an extremely low pH. But it takes energy to export
> those protons. Where does the energy come from? Not from turning Fe++
> to Fe+++, I think. Something else must be being oxidized and then
> released to solution. Sulfur? Phosphides? There are some trace
> metals like Mo and Cr that might be oxidized to a soluble form, but
> I would be surprised if the microbes could find enough of them to
> pay the expense of mining for them. Does anyone have a link to info
> on the overall metabolic scheme for these microbes?
All good questions, but I suspect a bit premature.
Bacteria are the putative agent for the tracks seen in the basaltic
glasses, but to the best of my knowledge, no one has yet identified an
actual culprit species or even caught any of them in the act.
The primary reason for the suspicion of bacteria as the tunnelling agent
are (i) the non-thermodynamic nature of the tunnels and (ii) the
occasional finding of DNA in the tunnels, but in this sort of work you
constantly have to remind yourself that you're quite possibly seeing
things that aren't (or were never) there.
Good scientific research always works right on the edge of complete
ignorance. Unfortunately, that leaves you quite vulnerable to being
totally wrong.
Wirt Atmar
Wirt Atmar
The article by Neil Banerjee and his co-authors appeared in 23 April
2004 issue of Science. Unfortunately, if you don't maintain a
subscription to the journal, you can't access the article.
However, I have copied below an accompanying bit of explanation
regarding their findings that appeared in the same issue.
Neil's talk, which was the original subject of this thread, very closely
replicates the material that appears in their Science paper, which is
available for free, and quite enjoyable to boot.
Wirt Atmar
====================================================
Science 23 April 2004:
Vol. 304. no. 5670, p. 503
DOI: 10.1126/science.304.5670.503
News of the Week
PALEONTOLOGY:
New Biomarker Proposed for Earliest Life on Earth
Richard A. Kerr
Recognizing life's remains becomes increasingly difficult as they shrink
in size and increase in age. Little wonder paleontologists and
astrobiologists have taken to tussling over what was and wasn't alive
billions of years ago on Earth or on Mars.
Now, on page 578, a group of geoscientists takes a newly developed
marker of recently past life and applies it to some of the oldest rocks
on the planet. The researchers report the discovery of microscopic
tubules in 3.5-billion-year-old sea-floor rock that strongly resemble
microtubules apparently bored in modern sea-floor rock by
microorganisms. If the ancient borings indeed had a biological origin,
life was firmly established just a few hundred million years after the
end of the rain of giant impacts that had repeatedly sterilized the
young Earth. But, true to the field's recent history, the first
application of the microtubule biomarker to ancient rocks is getting a
mixed reception.
This new contender for oldest biomarker on Earth comes from South
African rock that formed as lava oozed across a sea floor 3.5 billion
years ago. Geologists Harald Furnes and Neil Banerjee of the University
of Bergen, Norway, and their colleagues have found tubular structures
sprouting from mineral-filled fractures in what was once the glassy rind
of submarine lavas resembling a pile of pillows. These ancient
microtubules, which average 4 micrometers in width and 50 micrometers in
length, bear a striking resemblance to microtubules in modern sea-floor
pillow basalts.
In the past decade, Furnes and other researchers have built a case for
modern microtubules, at least, being the tracks of rock-eating
microorganisms. These geologically young microtubules have the right
size and shape to have been formed by micrometer-scale organisms. They
can contain lingering organic remains and nucleic acids or just enhanced
amounts of carbon and nitrogen, building blocks of life. The carbon is
isotopically lighter, which could be life's doing. And in the lab,
particular microbes have been shown to eat their way into rock and
glass, taking up essential nutrients stored there such as phosphorus and
iron. Still, yearlong experiments produce only shallow pits.
Furnes and his colleagues found most of those characteristics--similar
size and shape, signs of organic matter, and light carbon isotopes--in
the microtubules from the South African rocks, convincing them that that
they have found a "3.48-billion-year-old biomarker." Others agree. "I've
looked at hundreds of rocks" while studying modern microtubules, says
petrologist Martin Fisk of Oregon State University in Corvallis. "To me,
it's unequivocal that the textures they see were created by
microorganisms. I think they've got the best evidence I've seen for life
at that time." Other equally ancient signs of life have all come in for
criticism lately (Science, 24 May 2002, p. 1384).
Others are a bit more cautious. The South African microtubules "do look
just like modern analogs in deep-sea glasses," says microbial geochemist
Jennifer Roberts of the University of Kansas in Lawrence. But although
compelling, the evidence "isn't a smoking gun," she adds. Abiotic
chemical reactions, she notes, might move a few elements and isotopes
around while carving out tubules in glass.
Paleontologist Martin Brasier and his colleagues at the University of
Oxford, U.K., think they have an example of just such ancient abiotic
borings. Unaware of Furnes's latest work, they were pursuing
microtubules in Australian sea-floor lavas of the same age. "There's no
doubt theirs and ours are the same sort of thing," says Brasier, but "we
have a completely different interpretation of what's going on." In
analogy to examples previously reported by others, Brasier believes that
decomposition--possibly of organic matter--produced fluids that drove a
mineral grain into the glass as chemical reactions at the grain ate into
the glass, sort of like a corrosive-tipped pile driver. "We still do not
know whether life is needed," says Brasier.
With the inevitable uncertainties inherent in any one biomarker, "we're
really going to need to look at a number of pieces of biological
evidence," says Roberts. That's the approach--still unsuccessful after 8
years--that proponents of biomarkers in martian meteorite ALH84001 have
followed. In the meantime, Fisk is upping the ante a tad. At last
month's Lunar and Planetary Science Conference in Houston, Texas, he and
his colleagues presented examples of microtubules in the mineral olivine
that resemble those in volcanic glass. Then he made a planetary
connection by showing similar "tubelike alteration" in Nakhla and
Lafayette, two martian meteorites.
====================================================
Tom Hendricks
> However, I have copied below an accompanying bit of explanation
> regarding their findings that appeared in the same issue.
Thanks, much appreciated.
. If the ancient borings indeed had a biological origin,
> life was firmly established just a few hundred million years after the
> end of the rain of giant impacts that had repeatedly sterilized the
> young Earth. But, true to the field's recent history, the first
> application of the microtubule biomarker to ancient rocks is getting a
> mixed reception.
More and more the evidence points to an earlier origin for life.
Yet we keep coming up on the 'rain of giant impacts' that
'repeatedly sterilized the young earth."
I wonder if it isn't time to challenge that idea. One alt scenario
suggested that the moon impacts were just other bollides in the
same orbit as the moon, remnants of the collision with earth that
caused
the moon in the first place. Thus most of the moon craters were
restricted to the moon and did not impact the earth.
We aren't that sure about early life. Are we all that more sure of this
sterilizing period?
Something has to give here. We can't have both life sprung in
a somewhat evolved form, and no time to evolve that form.
And panspermia seems to be a red herring to me.
Perplexed in Peoria
"Tom Hendricks" <tomhend...@cs.com> wrote in message news:e0f0js$1qtq$1...@darwin.ediacara.org...
> More and more the evidence points to an earlier origin for life.
> Yet we keep coming up on the 'rain of giant impacts' that
> 'repeatedly sterilized the young earth."
>
> I wonder if it isn't time to challenge that idea. One alt scenario
> suggested that the moon impacts were just other bollides in the
> same orbit as the moon, remnants of the collision with earth that
> caused
> the moon in the first place. Thus most of the moon craters were
> restricted to the moon and did not impact the earth.
>
> We aren't that sure about early life. Are we all that more sure of this
> sterilizing period?
>
> Something has to give here. We can't have both life sprung in
> a somewhat evolved form, and no time to evolve that form.
> And panspermia seems to be a red herring to me.
To me too. Though the time available from the last big impacts
around 4.0 - 3.8 Ga to the Apex chert and Barberton greenstone
'fossils' is 300 million years. Seems like plenty of time to me.
Nonetheless, you will be happy to hear, Tom, that the first
chapter of "The RNA World" (2nd ed) supports your arguments
that there may not have been a severe bombardment as late as
3.8 Ga. I was very surprised to read that they even consider
reasonable your idea that only the moon got hit.
The chapter is available online here:
http://rna.cshl.edu/content/free/chapters/01_rna_world_2nd.pdf
Well worth reading. However, you may be disappointed with its
dismissal of the Miller experiment, the "soup", and the
possibility of concentrating organics in tidal pools.
An excerpt (about the Miller experiment):
However, it is now held to be highly unlikely that the
conditions used in these experiments could represent
those in the Archean atmosphere. Even so, scientific
articles still occasionally appear that report experiments
modeled on these conditions and explicitly or tacitly
claim the presence of resulting products in reactive
concentrations “on the primordial Earth” or in a
“prebiotic soup.” The idea of such a “soup” containing
all desired organic molecules in concentrated form in
the ocean has been a misleading concept against which
objections were raised early (see, e.g., Sillén 1965).
Nonetheless, it still appears in popular presentations
perhaps partly because of its gustatory associations.
And also:
A related casualty of the organic aridity of a
near-neutral atmosphere is the concept of solution
in the ocean, taken for granted almost automatically
in much of the literature as the site of early chemical
evolution toward complex biomolecules. The dilution
in the ocean of soluble compounds from any weak source
is forbidding; already sparse, unstable molecules
introduced in a volume of 1.3 × 10^9 km^3 of seawater
are mutually unreactive and hardly retrievable by
evaporation or other means.
William Morse
> Jim asks:
>
>> These glass-eating, or glass tunneling, microbes are fascinating, but
>> where does their energy come from? Presumably they are
>> chemolithoautotrophs. By definition, glasses are higher in energy
>> than crystals of the same composition. And presumably there may be
>> some decrease in energy due to simply dissolving the glass and
>> releasing the more soluble ions into solution. But it doesn't seem
>> easy to turn this kind of diffuse energy supply into phosphate bonds
>> for organism growth and maintenance. To do that it would seem that
>> you need redox chemistry. So what element is being oxidized so that
>> carbon can be reduced?
>>
>> Laboratory glassware is not generally soluble in acids. I wonder
>> whether basaltic glasses are more susceptible. I do note that an
>> organism living in a tunnel and exporting protons to the face of the
>> tunnel can probably generate an extremely low pH. But it takes
>> energy to export those protons. Where does the energy come from?
>> Not from turning Fe++ to Fe+++, I think. Something else must be
>> being oxidized and then released to solution. Sulfur? Phosphides?
>> There are some trace metals like Mo and Cr that might be oxidized to
>> a soluble form, but I would be surprised if the microbes could find
>> enough of them to pay the expense of mining for them. Does anyone
>> have a link to info on the overall metabolic scheme for these
>> microbes?
>
> All good questions, but I suspect a bit premature.
Very true, but it is hard to resist a chance to posit a just-so story.
> Bacteria are the putative agent for the tracks seen in the basaltic
> glasses, but to the best of my knowledge, no one has yet identified an
> actual culprit species or even caught any of them in the act.
>
> The primary reason for the suspicion of bacteria as the tunnelling
> agent are (i) the non-thermodynamic nature of the tunnels and (ii) the
> occasional finding of DNA in the tunnels, but in this sort of work you
> constantly have to remind yourself that you're quite possibly seeing
> things that aren't (or were never) there.
Elevated levels of C, P, and N were also found in the weathering
features. The article I found (Science 8/14/98) noted that reduced iron,
manganese, and sulfur were available as electron donors. Acidic etching
seems a little dubious - typically this requires hydrofluoric acid. Is
there any chance that carbon is substituting for silicon in portions of
the glass?
Yours,
Bill Morse
Tom Hendricks
> > We aren't that sure about early life. Are we all that more sure of this
> > sterilizing period?
> >
> > Something has to give here. We can't have both life sprung in
> > a somewhat evolved form, and no time to evolve that form.
> > And panspermia seems to be a red herring to me.
>
> To me too. Though the time available from the last big impacts
> around 4.0 - 3.8 Ga to the Apex chert and Barberton greenstone
> 'fossils' is 300 million years. Seems like plenty of time to me.
>
> Nonetheless, you will be happy to hear, Tom, that the first
> chapter of "The RNA World" (2nd ed) supports your arguments
> that there may not have been a severe bombardment as late as
> 3.8 Ga. I was very surprised to read that they even consider
> reasonable your idea that only the moon got hit.
That idea is not mine. I read it from others - but I've forgotten
the originator's name
> introduced in a volume of 1.3 * 10^9 km^3 of seawater
> are mutually unreactive and hardly retrievable by
> evaporation or other means.
I don't think Miller has to hide his awards just yet.
IF the Miller Urey experiment does not explain the first
phase of life - the producing of the necessary organics,
then we really are back to square one. And one asks
well how then? And what does?
On the other hand, his work is so open to just about any
environmental condition and or force (once the necessary gases are
there)
that it seems logical that it happened that way somehow. If other
factors say no - then we must look for ways that both fit.
I think the M-U experiments are such important clues that
we shouldn't knock them out just yet.
Personally I think we just move the clock back. And even
without the heavy bombardment - there is still more heat,
more shock from meteorites, more lightning,
shallower seas, more volcanic spewing of
methane, water, etc.; more environmental forces, more
chemical activity, more greenhouse gases - etc.
Let's take it back and not be so worried about every
meteor, as if it alone could knock out life. More and more I think this
so called danger time was a necessary part of the initiation
of life.
Perplexed in Peoria
"Tom Hendricks" <tomhend...@cs.com> wrote in message news:e0uhs1$2aqh$1...@darwin.ediacara.org...
[Re criticisisms of relevance of Miller experiment to OOL]
> I don't think Miller has to hide his awards just yet.
> IF the Miller Urey experiment does not explain the first
> phase of life - the producing of the necessary organics,
> then we really are back to square one. And one asks
> well how then? And what does?
>
> On the other hand, his work is so open to just about any
> environmental condition and or force (once the necessary gases are
> there) that it seems logical that it happened that way somehow.
> If other
> factors say no - then we must look for ways that both fit.
Or we can observe that perhaps the 'building blocks of life'
are not prerequisites for life and proceed to build scenarios
on that basis. An autotrophic basis.