Text 662, 124 rader
Skriven 2004-11-05 12:26:00 av Michael Ragland (1:278/230)
Ärende: Response to Robert Karl S
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This "appears" to possibly be examples of "chemosynthetic" organisms
but the researchers acknowledge they are poorly understood. My own
view is chemosynthesis preceded photosynthesis and we would not be
alive today as an organism had it not been for chemosynthesis although
it was photosynthesis which allowed life to incredibly flourish and
diversify and managed to kill off many chemosynthetic organisms.
http://www.geo.unimib.it/Conisma/KIELBIO.htm Mud diapirs and mud
volcanoes are present at different sites along the crestal area of the
Mediterranean Ridge. The geological deformation of this accretionary
prism pressurizes the circulating fluids which are expelled from
sediments. Relatively dense macrobenthic communities, mainly composed
of mollusks were observed in cores and video images recorded at the
top of the Napoli Dome, S of Crete. A box-corer taken (fig. 1-2) near
a "black spot", showed 3 cm of fluid, surficial, pteropod mud
containing some lucinids (fig.3). Other lucinids and vesicomyids
(fig.4) were recognized on the top of other bottom samples collected
on the Napoli Dome. All these taxa are known to host bacterial gill
symbionts, which exploit the reduced gases emitted from the mud
volcano for the synthesis of organic compounds. The chemosynthetic
organic compounds provide energy to the molluscan hosts, allowing them
to thrive in these otherwise inhospitable, extreme environments. The
precise type of chemotrophy which characterizes the bacteria linked to
the anoxic lakes and to the mud volcanoes and the different type of
producers involved in these trophic webs are still far to be
completely understood. C.Corselli, D.Basso (1996) -First evidence of
benthic communities based on chemosynthesis on the Napoli mud volcano
(eastern Mediterranean). Marine Geology, 132: 227-239 
ACKNOWLEDGEMENTSWe are grateful to the Italian Consiglio Nazionale
delle Ricerche (CNR) for the ship time of the R/V Bannock and R/V
Urania. Funds from Consiglio Nazionale delle Ricerche (CNR), and EU
MAST Programme Projects: MARFLUX (MAST I), PALEOFLUX (MAST II), SAP
(MAST III). EU-Workshop on Extreme Marine Environments, Kiel 19-22
November 1998 Re: Is chemosynthesis older than photosynthesis?Date:
Thu Mar 16 13:23:34 2000Posted By: Neil Saunders, Post-doc/Fellow,
Molecular Cell Physiology, Vrije UniversiteitArea of science:
EvolutionID: 953094577.Ev Message:Hi Raul, Thanks for this question-it
is a good one. Here is the short answer: yes, chemosynthesis is a more
viable option for early life and yes, we believe that it predates
photosynthesis. Now for the longer answer! There is a lot of debate
about the composition of the early earth. It was hot and therefore
volcanically active. There would have been large out- gassings of
water vapour into the atmosphere and frequent electrical storms, all
as depicted in the pictures that you mention. In the 1950's,
biologists Harold Urey and Stanley Miller tried to simulate the early
atmosphere by passing electrical discharges through mixtures of water
vapour, methane and ammonia, and they showed that many basic
biochemicals could be formed in this way, including sugars, amino
acids and the bases of nucleic acids. These experiments have shaped
the way that scientists think about how life started ever since. The
experiments assumed that the early atmosphere was reducing-that is,
rich in hydrogenous compounds such as methane. Since then there has
been much debate about this, with many scientists now believing that
the atmosphere was less reducing than previously assumed. However, one
thing we are quite sure of is that the early atmosphere was not
oxygen-rich. The oldest known rocks contain very low amounts of
"banded iron ores", formed when iron reacts with free oxygen. These
types of ore increase over time, starting about 2.5 billion years ago.
So it seems that free oxygen appeared and increased over time, and the
only source of oxygen that we know for this is photosynthesizing
micro-organisms. But we have fossil evidence for simple, single-celled
organisms long before this time. They must have had very simple
metabolisms and the simplest that we know of are chemosynthetic. They
were probably similar to the kingdom of micro-organisms called
Archaea, that exist today. They often live in extreme environments and
can derive energy by oxidising simple compounds or even elements, like
iron or hydrogen. Photosynthesis had to wait for 2 things: (1) the
production of chlorophyll, or a similar compound, that could capture
energy from sunlight, split water and generate hydrogen and (2) the
ability to combine that hydrogen with carbon dioxide to make sugars.
But once photosynthesis was established, the organisms that could
perform it spread to take over the earth. Of course, the new oxygen
was toxic to the previous inhabitants and they were banished to the
extreme corners of the earth for ever! And in time, organisms evolved
that could tolerate and use the oxygen.This is a vast and fascinating
topic, with many unanswered questions and contentious areas. If you
want to read more, a good discussion of the early earth can be found
in a great book, "Life: An Unauthorised Biography" by Richard Fortey.
There are also excellent resources at:http://www.talkorigins.org/This
is the Talk.Origins archive, which discusses many evolutionary topics,
including the early earth.Neil Saunders  Current Queue | Current Queue
for Evolution | Evolution archives Try the links in the MadSci Library
for more information on Evolution.  MadSci Home | Information | Search
| Archives | Mad Library | MAD Labs | MAD FAQs | Ask a question | Join
Us!  MadSci Network, webadmin@www.madsci.org© 1995-2000. SS16
Permeable Sediments - Physics, Biology and GeochemistryDate: Thursday,
June 17, 2004Time: 10:00 AMLocation: Room 100 Biddanda, B A Grand
Valley State University, Muskegon, USA, biddandb@gvsu.eduJohengen, T H
University of Michigan, Ann Arbor, USA, johengen@umich.eduRuberg, S 
NOAA Great lakes Environmental Lab, Ann Arbor, USA,
steve.ruberg@noaa.govRediske, R  Grand Valley State University,
Muskegon, USA, redisker@gvsu.eduKendall, S  Grand Valley State
University, Muskegon, USA, kendalsc@gvsu.eduMeadows, G  University of
Michigan, Ann Arbor, USA, gmeadows@engin.umich.eduColeman, D 
Institute for Exploration, Mystic, USA, dcoleman@ife.org ECOLOGY OF A
SUBMERGED SINKHOLE IN LAKE HURON: IS THERE EVIDENCE FOR
CHEMOSYNTHESIS, AND CHEMOSYNTHESIS-BASED HETEROTROPHIC
PRODUCTION?Dissolution of Silurian-Devonian aquifer in the Lake Huron
Basin has produced karst formations (sinkholes) through which
groundwater seeps into the lake bottom. Using a remotely operated
submersible, we explored one such sinkhole ecosystem during September
2003. Venting groundwater at 100m depth was 4-5 C warmer and had
10-fold higher conductivity than ambient lake water. A 1-2m thick dark
cloudy nepheloid layer with a strong hydrogen sulfide odor prevailed
just above the venting area. This layer was characterized by very high
concentrations of organic matter (up to 400 mgC/L having a C:N molar
ratio of 8-9), sulfate and chloride. Bromide, acetate and formate were
also present at lower concentrations. Compared to surface water, vent
water was characterized by 10-fold higher dissolved organic matter,
bacterial biomass as well as heterotrophic bacterial production.
Significant uptake of 14C-bicarbonate in dark incubations provided
preliminary evidence for occurrence of chemosynthesis in this
sulfide-rich, oxygen-poor, organic-rich, aphotic environment. Could
the observed high rates of heterotorphic production be supported by
intense chemosynthetic production of organic matter within this
submerged sinkhole ecosystem in the Laurentian Great Lakes?           
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