Re: Lecture of the Week: Part II: Could We Tell Life If We Saw It?

"Wirt Atmar" <atmar@xxxxxxxxxxxxxxxxx> wrote in message news:e09btv$2gnb$1@xxxxxxxxxxxxxxxxxxxxxx
The webpage for the lectures is:

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)

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.
[snip to related research by Fisk]
"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?