Life’s Limit

Life’s Limit

"You don’t have to go far to see extremeophiles here in northern California," Rocco Mancinelli once told a crowd of astronomy lovers in a Bay Area lecture hall. People giggled. But Mancinelli wasn’t talking extreme life styles or fashion; he was talking about microbes. Specifically, salt-loving halophiles that thrive in the crimson patchwork of evaporation pools–those commercial salt extraction ponds clustered along southern portions of the San Francisco Bay. Tiny creatures that thrive in harsh conditions on Earth are of great fascination to astrobiologists. Mancinelli describes his area of expertise:

Astrobiology is an enormous field with ambitious goals. It seeks to understand the origin and evolution of life on Earth, to determine if life exists elsewhere, and to predict the future of life on our planet and in the rest of the universe. My own work within this field is also cross-disciplinary, and touches upon several elements of this big picture.

In order to understand how life began on Earth I study the origin of the chemical compounds that make up living organisms, and what kind of chemistry and geology are necessary to create an environment capable of supporting life.

My research interests encompass ecology, physiology, biogeochemistry, and geochemistry. Skills and techniques from all these fields help me better understand how an environment will shape, sustain and constrain the origin and evolution of life.

I currently examine four living systems in these studies. I study:

  • halophiles, salt-loving microbes in the evaporitic salt crusts that form along marine intertidal zones;
  • microbial mats inhabiting diverse environments (for example, the intertidal area of the Baja coast, the alkaline and acid hot springs of Yellowstone National Park, hypersaline lakes and the perennially ice-covered lakes in the dry valleys of Antarctica;
  • areas where rock (desert) varnish occurs; and
  • the space environment in Earth orbit.

I examine the organisms in these unique and challenging environments, study the mechanisms by which they survive and flourish in their current environment, and subject them to further rigors to test the limits of their survival mechanisms.

Cross section of soil layers, with red layer at top.
Laterites are layers of soil colored red from high concentrations of iron. This example is from Brazil, and illustrates the geological remnants of ancient microbial action. Credit: Univ. of Colorado/Joe Smyth.

The results of such experiments allow me to model the interactions of microbes with other microbes, and with their environment, and the role of nitrogen in these living systems. These models help us formulate hypotheses about the evolution of the nitrogen cycle, and the role exogenous sources of fixed nitrogen in the physiology of nitrogen metabolism, biogeochemistry and microbe community structure.

We also use these models to extrapolate from what is known about the environment (geochemistry and climatology) of early Mars in an attempt to determine the potential for life to evolve on that planet. Nitrogen seems a the key element for two reasons: 1) It (fixed-N) is an important limiting nutrient in many terrestrial systems; and 2) It appears that N would have been one of the most important limiting nutrients on Mars as well.

A common thread ties all my research projects together; I am searching for the definitive environmental limits in which life can arise and evolve on planets. Seeking these limits leads my research into examining the potential for life to arise elsewhere in the solar system, for example, Mars. Because Mars shares many common attributes to Earth, (this is particularly true for its early planetary history), it is the only other planet in the solar system that had potential for life to arise. This makes Mars a particularly appropriate test-bed for assessing the probability, and environmental parameters necessary for life’s origin and early evolution.

We know that the essential major and minor biogenic elements exist on Mars, and that its temperatures, pressures and radiation levels would not have precluded the origin and evolution of life. The primary factor in determining if life could have arisen on Mars lies in determining if liquid water existed on its surface for sufficient time. The history of water lies within the mineralogy of the rocks.

My research with Mars soil analogs (using differential thermal analysis coupled with gas chromatography) will allow me to interpret data from the suite of upcoming Mars missions and help answering the question of whether Mars ever possessed sufficient liquid water for life to evolve. This in turn may elucidate and define the limits for the origin and early evolution of life on earth.

And the future? This astrobiologist who studies salt samples from the red evaporation ponds near San Francisco would one day like to scrutinize a soil sample from the Red Planet. For Mancinelli, it’s all about finding limits.

Related Web Pages

Rocco Mancinelli
SETI Institute
NSF Life in Extreme Environments (LEXEN) Program
Introduction to the Archaea – Life’s extremists
Atlantis Diaries XI: Encore
Atlantis Diaries X: Reaction Zone
Atlantis Diaries IX: Rescue
Atlantis Diaries VIII: Science Basket
Atlantis Diaries VII: Poseidon’s Excellent Adventure
Atlantis Diaries VI: Portal on the Past
Atlantis Diaries V: Hump Day
Atlantis Diaries IV: Eating Iron
Atlantis Diaries III: Exploring Alien Eco-Regions
Atlantis Diaries II: First Dive
Atlantis Diaries I: Leaving Port
Life from Rocky Reaction
Lost City Expedition
Discovery of Lost City vent field-Univ. Washington

Univ. Washington School of Oceanography
Cafe Methane
Life without Volcanic Heat