Exobiology and The Search for Extraterrestrial Life
Absence of evidence is not evidence of absence,” Carl Sagan
Tomoko Adachi, The Evergreen State College, Olympia, WA

Did Life originate only on Earth?

In August 1996, NASA scientists announced that a microbe found in the Martian meteorite ALH 84001 might have once flourished on the red planet. A series of controversies in the scientific community followed this announcement. In 1997 a scientist, Robert Folk published his paper that discussed the discovery of nanobacteria within a rock in a hot spring. Folk’s summary of his 1997 paper: Nanobacteria are very small living creatures in the 0.05 to 0.2- micrometer range. They are enormously abundant in minerals and rocks, and probably run most of the earth’s surface chemistry. It is contended that they are responsible for a great deal of mineral precipitation as well as conversion of igneous minerals to soils, and the corrosion of metal.

Martian Meteorite
ALH 84001
Search for Past Life 
Nanobacteria found in a rock in a hot spring in Italy.
ROBERT L. FOLK
Microbe found in the Columbia River Basalt
Photo: NanoBacteria

References and bibliography is in the back.

While the scientist and researchers was fussing about these Earthbound discoveries, the Hubble Telescope made astronomer possible to observe deep space and telltale objects. Astronomers found our Solar system is surrounded by clouds of comets and asteroids (see Oort Cloud) that extend to the nearest star Alpha Centauri (4.0x10^13 km, 4.2 light-years). The space between stars is not empty; there are materials such as gas molecules and dust grains. Giant Molecular Cloud is one such that contains hydrocarbon compounds such as hydrogenated amorphous carbon (HAC), and polycyclic aromatic hydrocarbon (PAH). These organic compounds were also found in some comets. Implication is significant that these organic matter may serve as the building blocks for life on Earth.Another intriguing discoveries are Extremophiles. They are microbes that can thrive in extreme environments such as: high temperature (above boiling point), sulfuric acid solution (volcanic deep-sea vents), among salt crystals, radioactive radiation such as gamma and X rays and UV light. Implications of extremophiles are significant. These die-hard organisms are highly sophisticated in their survival schemes and can survive for millions of years. The chemical reactions that drive biological activity are now known to be much more diverse than anyone suspected before. It is now clear that reactions involving hydrogen, methane, sulfur or iron can sustain biological activity.

Last year, the research scientists of the Pacific Northwest Laboratory in Richland, Washington, discovered bacteria deep within basalt rock beneath the Columbia River that thrive only on Hydrogen. This hydrogen is continually produced by chemical reactions between water and crushed basalt.

The search for life on Mars has begun.
The final answer on whether life has ever existed on Mars will probably only come after careful studies of Martian samples are sent back to Earth. In 2005, NASA plans to bring back samples from one or more sites. The ultimate answer for the riddle, the origin of life may soon be answered.
 
 
 

The Oort Cloud
The solar system is surrounded by clouds of comets and asteroids that extends to 50,000 AU (Astronomical Units). One AU is the distance from Sun to Earth, and the distance from Sun to Pluto is about 30 AU. It is also about .8 light years to the cloud. This extended system has interacted with other star systems or a Giant Molecular Cloud. The range of the diameter of the Giant Molecular Clouds is from 50 to 300 light-years. We detected its CO (carbon monoxide) emission. (wavelength is 2.6 mm) Giant Molecular Clouds contain hydrocarbon compounds such as HAC, PAH, and polymer polyoxymethylene (POM) These carbonaceous compounds were detected in comets from the Oort cloud.
 
 

The Archaea
Researchers say that the heat and geochemical conditions in volcanic regions may be similar to conditions that existed on the young, cooling Earth. The volcanic microbe is different from the two other basic branches of life: bacteria and eukaryotes. The prokaryotes are the bacteria, while eukaryotes are the so-called higher formed of life, including humans, plants and animals. Archaea are thought to have a common ancestor with bacteria, but billions of years ago the third domain, eukaryotes, broke off from archaea, eventually developing into plants, animals and us. Archaea include microbes that live at the extremes environment on Earth. As such, archaea are the extremophiles.
 
 
 
The bacteriologist, Thomas Brock started probing the hot springs in Yellowstone National Park in the 1960s. At the time, biologists thought life would not tolerate temperatures anywhere near 80 °C. But Brock kept find bacteria. He found organisms that could live and reproduce near the temperature of boiling water – 100 °C. Some scientists have suggested that as such, archaea may represent the earliest form of life Earth and thus are considered to be the most likely form of life existing on other planets. 
Photo is adopted from:
BRAVE NEWBiosphere

The Search for Extremophiles
The most obvious example of a significant physical limit on life is the need for liquid water. The life made with carbon compounds floating in water does have some absolute constraints based on the nature of our chemistry. On Earth, we have environments ranging from the superheated waters of deep-sea volcanic vents to the ultra-dry biter cold of the Antarctic dry Valleys. We find organisms living in caves dripping with sulfuric acid and others thriving in intensely alkaline solutions. We find creatures happily existing in saturated salt solutions, enduring megadoses of ionizing radiation, or deriving their food and energy sources from inorganic materials like manganese, iron, and sulfur compounds.

Extremophiles who boldly thrive where no other life form would go.

Deep and Hot - Deep-Sea Volcanic Vent 
Bacteria convert chemicals from the sulfur-rich fluid spewed out of vents to energy, in a process called chemosynthesis. Other animals in the community eat the bacteria, harbor bacteria in their bodies, or eat bacteria eaters. Vent worms have no mouth or digestive tract. Instead, chemosynthetic bacteria living in their tissues provide nourishment.

No-light, No Oxygen, Dark and very Hot or Cold , Deep Dwellers
Microbes are living in the deepest gold mine in South Africa and 3 km below ground in South Carolina, where the temperature of the rock reaches 60 °C to 75 °C.
 
 

Methane Ice worm on Gulf of Mexico Sea Floor
The worms were observed using their two rows of oar-like appendages to move about the honey-combed, yellow and white surface of the icy mound. The researchers speculate that the worms may be grazing off chemosynthetic bacteria that grow on the methane or are otherwise living symbiotically with them. Some Microbes have developed DNA Repairing System (Radiation-resistant bacteria may clean up the nation’s worst waste sites.) The radiation resistant microbe, Dienococcus radioduran has an ability to repair genetic damage. This ability the has allowed the microbe to be used for clean up the nation’s worst problem; the nuclear waste which includes the legacy of the cold war. Deinococcus radiodurans is resistant to ionizing radiation, and revived the idea that comets seeded planets with the precursors of life, or even life itself.

Deinococcus radiodurans Could Survive Interstellar Journeys.
The bacterium shrugs off doses of radiation many thousands of times stronger than those that would kill a person. Only a radiation-tolerant bacterium such as D. radiodurans could survive interstellar journeys. This idea revived the researchers motive to search for extraterrestrial life on other planets such as Mars, Jupiter’s moon: Europa and Io, and Titan, the moon of Saturn.
 
 

ASTROBIOLOGY
The study of Extremophiles has lead scientists to discuss the question of whether life originated as a result of simple straightforward chemical reactions in an appropriate environment. Only in the last decade or two, and especially in the last few years, have these theories all come together to provide a compelling argument suggesting that life could exist elsewhere in our solar system and may even be widespread throughout the galaxy. With this argument comes a strong intellectual basis for understanding and searching for life, either in our own solar system or on planets around other stars. This drive has become a major centerpiece of NASA scientific missions, whether it be in the form of looking for life on Mars, liquid water and possible life on Europa, or Earth-like planets around other stars.
 
 

Jupiter’s Icy moon Europa, taken by NASA’s Galileo space probe photo by JPL
Roughly the size of our Moon, Europa is thought to contain an ocean of water nearly twice as voluminous as all of Earth’s oceans. The features also provide evidence that water, heat and organic compounds may have combined to create an environment suitable for the start of life. It has been suggested that hydrothermal life supporting vents similar to these on earth may exist in the ocean beneath the ice sheets of Europa. Also a new idea has emerged, suggesting that the heavy doses of lethal radiation surrounding Jupiter might spur chemical reactions on its tiny satellite, providing fuel for life in the suspected liquid ocean below.
 
 

Reference and Bibliography

The discover of a second genesis within our solar system would suggest that life develops wherever it can. (“The Search for Extraterrestrial Life,” by Carl Sagan; Scientific American, October 1994)

Brock Biology of Microorganisms, Madigan, Martindo, Parker, Ninth Edition

Deadly radiation could power life on Europa, Robert Roy Britt, January 2000

Cosmic-ray Particles and interstellar ice, THE ASTROPHYSICAL JOURNAL, 484:487498, 1997 July 20

Deep Sea Hydrothermal Vents, University of Washington School of Oceanography

Exploraquarium Radiation-resistant bacteria may clean up the nation’s worst waste sites, John Travis, Dec. 1998

Life Beyond Earth, Joel Achenback, National Geographic, January 2000

The Oort Cloud, Paul R. Weissman, Scientific American, Sep98, Vol.279 Issue 3, p84

Comet Reservoir Gets More Real, R. Cowen, Science News, 06/07/97, Vol. 151 Issue 23, p352

Hidden Worlds: Hunting for Distant Comets and Rogue Planets, Freeman J. Dyson, Sky & Telescope, Jan94, Vol. 87 Issue 1, p26

Beyond Pluto, Michael D. Lemoni, Time, 9/28/92, Vol. 140 Issue 13, p59

Odd Visitor From The Oort Cloud, Constance Holden, Science, 10/10/97, Vol. 278 Issue 5336, p229

Methane Ice Worms discovered on Gulf of Mexico Sea Floor, The Eberly College of Science

Chemical Evolution of Carbonaceous Material in Interstellar Clouds, W.W. Duley, School of Physics

Microbial Remnants from Mars?, SCIENTIFIC AMERICAN, March 19992

"SLiME" at Hanford hints at potential for microbes on Mars, Pacific Northwest Laboratory, October 24, 1995

Nanobacteria: surely not figments, but what under heaven are they?, Department of Geological Sciences, University of Texas, Austin Texas: http://www.geo.utexas.edu/Illite/index.html

Comets, the Oort Cloud and the Kuiper Belt http://cat.apg.ph.ucl.ac.uk/3c37/3c37-12.html

Photos in this paper are adopted from: NASA, Jet Propulsion Laboratory, ASTROBIOLOGY WEB SITE: http://www.astrobiology.com

NASA (Hot topics in Japanese) : http://spaceboy.nasda.go.jp/spacef/tour/j/cool_j.html

STARDUST: http://stardust.jpl.nasa.gov/

Deep-Sea Bioluminescence, MBARI: http://www.mbari.org/

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