Posted on 05/30/2008 1:35:19 AM PDT by LibWhacker
ScienceDaily (May 30, 2008) A new analysis of the Martian rock that gave hints of water on the Red Planet -- and, therefore, optimism about the prospect of life -- now suggests the water was more likely a thick brine, far too salty to support life as we know it.
The finding, by scientists at Harvard University and Stony Brook University, is detailed May 30 in the journal Science.
"Liquid water is required by all species on Earth and we've assumed that water is the very least that would be necessary for life on Mars," says Nicholas J. Tosca, a postdoctoral researcher in Harvard's Department of Organismic and Evolutionary Biology. "However, to really assess Mars' habitability we need to consider the properties of its water. Not all of Earth's waters are able to support life, and the limits of terrestrial life are sharply defined by water's temperature, acidity, and salinity."
Together with co-authors Andrew H. Knoll and Scott M. McLennan, Tosca analyzed salt deposits in four-billion-year-old Martian rock explored by NASA's Mars Exploration Rover, Opportunity, and by orbiting spacecraft. It was the Mars Rover whose reports back to Earth stoked excitement over water on the ancient surface of the Red Planet.
The new analysis suggests that even billions of years ago, when there was unquestionably some water on Mars, its salinity commonly exceeded the levels in which terrestrial life can arise, survive, or thrive.
"Our sense has been that while Mars is a lousy environment for supporting life today, long ago it might have more closely resembled Earth," says Knoll, Fisher Professor of Natural Sciences and professor of Earth and planetary sciences at Harvard. "But this result suggests quite strongly that even as long as four billion years ago, the surface of Mars would have been challenging for life. No matter how far back we peer into Mars' history, we may never see a point at which the planet really looked like Earth."
Tosca, Knoll, and McLennan studied mineral deposits in Martian rock to calculate the "water activity" of the water that once existed on Mars. Water activity is a quantity affected by how much solute is dissolved in water; since water molecules continuously adhere to and surround solute molecules, water activity reflects the amount of water that remains available for biological processes.
The water activity of pure water is 1.0, where all of its molecules are unaffected by dissolved solute and free to mediate biological processes. Terrestrial seawater has a water activity of 0.98. Decades of research, largely from the food industry, have shown that few known organisms can grow when water activity falls below 0.9, and very few can survive below 0.85.
Based on the chemical composition of salts that precipitated out of ancient Martian waters, Tosca and his colleagues project that the water activity of Martian water was at most 0.78 to 0.86, and quite possibly reaching below 0.5 as evaporation continued to concentrate the brines, making it an environment uninhabitable by terrestrial species.
"This doesn't rule out life forms of a type we've never encountered," Knoll says, "but life that could originate and persist in such a salty setting would require biochemistry distinct from any known among even the most robust halophiles on Earth."
The scientists say that the handful of terrestrial halophiles -- species that can tolerate high salinity -- descended from ancestors that first evolved in purer waters. Based on what we know about Earth, they say that it's difficult to imagine life arising in acidic, oxidizing brines like those inferred for ancient Mars.
"People have known for hundreds of years that salt prevents microbial growth," Tosca says. "It's why meat was salted in the days before refrigeration."
Tosca and Knoll say it's possible there may have been more dilute waters earlier in Mars' history, or elsewhere on the planet. However, the area whose rocks they studied -- called Meridiani Planum -- is believed, based on Mars Rover data, to have been one of the wetter, more hospitable areas of ancient Mars.
Tosca, Knoll, and McLennan's work was supported by NASA and the Harvard Origins of Life Project.
Ah, the dangers of single-point extrapolations. I’m sure that a rock sample from the Dead Sea or Salt Lake would prompt the same assessment....
What are the extremely halophilic organisms?
What organisms can survive water activity below .75?
Or below .50?
Just curious.
So you say again. That does not help your position or argument.
Here's a couple of clues for you. MOST scientific research isn't peer reviewed.
According to many posters here, it is not science if it is not peer-reviewed. Take it up with them. That still not justify believing something classed as "double secret".
From the pictures I've seen, abundant life is obvious right up to the margin of the "smoker" vent itself.
You've got sharp eyes if you can see bacteria and determine temperature and concentrations from pictures taken from submersibles.
I could give a crap what "many posters here" say. I'm a practicing scientist, and I know how the world of science actually works (INCLUDING "peer review").
"That still not justify believing something classed as "double secret""
Your choice. I've had may say. Believe it or not.
I suppose then you have little reason to be on this site posting on these particular threads. Especially when you do belittle those scientists that we all know are practicing science, whether their conclusions are right or wrong.
I respect your chosen profession, however, at the moment I believe the conclusions drawn by the authors of this study and not your "double secret" data and conclusions.
See the last line in my last post to “netmom”. It applies to you, too.
Calcium carbonate
Re: calcium carbonate
Thanks, Prof. I merely copied the heading on the picture.
Okay, Rhett. Your "absence" will not be missed.
I accidently took home a plastic bag of these deposits from Mono Lake on a trip through the area; Mark Twain commented on their excellent cleaning powers around the time he spent in Virginia City, Nevada.
Here’s a WIKI snip:
[Tufa is the name for an unusual geological form of calcite rock.
Tufa is a rough, thick, rock-like calcium carbonate deposit that forms by chemical precipitation from bodies of water with a high dissolved calcium content. Tufa is not to be confused with tuff, which is volcanic.
Tufa deposition occurs in seven known ways:
Mechanical precipitation by wave action against the shore. This form of tufa can be useful for identifying the shoreline of extinct lakes (for example in the Lake Lahontan region).
Precipitation from supersaturated hot spring water entering cooler lake water.
Precipitation in lake bottom sediments which are fed by hot springs from below.
Precipitation from calcium-bearing spring water in an alkaline lake rich in carbonates.
Precipitation throughout the lake as the lake dries out.
Through the agency of algae. Microbial influence is often vital to tufa precipitation.
Precipitation from cold water springs (for example in the foothills of the Rocky Mountains near Hinton, Alberta).
There are some prominent towers of tufa at Mono Lake and Trona Pinnacles in California, USA, formed by the fourth method mentioned above whilst submerged and subsequently exposed by falling water levels. Tufa is also common in Armenia.]
Thanks Prof. I always appreciate learning new things. I knew that Mono Lake approaches saturation levels of some of the chemicals in the water and that can lead to the growth of these towers.
Mars Rovers Sharpen Questions About Livable Conditions
Jet Propulsion Laboratory | February 15, 2008 | Guy Webster
Posted on 02/23/2008 12:11:53 PM PST by SunkenCiv
http://www.freerepublic.com/focus/chat/1975123/posts
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