Don Savage
Headquarters, Washington, D.C.                              March 
22, 1994
(Phone:  202/358-1547)

Diane Farrar
Ames Research Center, Mountain View, Calif.
(Phone:  415/604-9000)


RELEASE:  94-49

NASA DEVELOPS PLAN TO SEARCH FOR MARTIAN FOSSILS

   A scientist at NASA Ames Research Center, Mountain View, 
Calif., has developed a strategy to search for microfossils on the 
planet Mars.  His criteria are helping to guide site selections 
related to the search for evidence of past life on Mars during 
upcoming Mars missions planned for later this decade. 

   "Our focus in the search for life (exobiology) on Mars has 
shifted to the search for ancient life because of the formidable 
conditions on the martian surface," said Dr. Jack Farmer.  Farmer 
is a paleontologist and geologist at Ames. 

   Exobiology is the study of the origin, evolution and 
distribution of life in the universe.  Farmer calls his newly 
invented discipline exopaleontology. 

   Farmer, with colleagues at Arizona State University, has 
catalogued and prioritized the sites on the martian planet most 
likely to conceal well-preserved microbial fossils.  He bases his 
strategy on the principles of Precambrian paleontology, the study 
of the Earth's earliest fossil record.

   The Precambrian era includes more than 90 percent of Earth's 
history.  Beginning before the time of the oldest Earth rocks 
dated 3.9 billion years ago, it continues to the explosion of 
complex multicellular life of about 540 million years ago. 

   Many scientists think that ancient Mars was a much warmer, more 
volcanically active planet with a dense atmosphere and abundant 
water. 

   The largest volcano in the solar system is on Mars.  Olympus 
Mons, probably now dormant, is three times the height of Mt. 
Everest.  River channels and lake basins carved into Mars' 
now-dusty terrain show vast amounts of water were once present on 
the planet's surface. 

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   The channels and lake basins are concentrated in the oldest, 
most heavily cratered terrains of Mars.  These areas are believed 
to be the same age as the earliest microbial fossils on Earth -- 
about 3.5 billion years old, Farmer said. 

   Since microbial communities developed on Earth in less than a 
billion years, it is plausible that organisms also developed on an 
early warm and wet Mars, he said. 

   If life developed on Mars, it is likely to have left a fossil 
record.  According to Farmer, the best locations to hunt for 
martian fossils are where nutrient-rich water once bubbled to the 
surface as hot springs. 

   Farmer, with Drs. David Des Marais of Ames and Malcolm Walter 
from Australia, has studied hot spring deposits in Yellowstone 
National Park to learn how to recognize them on Mars.  

   "Where organisms coexisted with early mineralization, we have 
the potential for preserving soft-bodied microbes, sometimes for 
billions of years," he said. 

   "The hot water bubbling off carbon dioxide gases creates 
alkaline conditions.  This encourages minerals like silica and 
carbonate to separate out.  The precipitating minerals encase and 
bury organisms and even entire microbial mats," he said. 

   Silicous thermal springs are the best places to look because 
silica is relatively stable and has a long residence time in 
Earth's crust, Farmer said.  Carbonates are more soluble than 
silica, he said, but can still preserve soft-bodied microorganisms 
for billions of years.  

   Microbes also coexist with precipitating minerals in 
evaporating lakes like Mono Lake in California, another site being 
studied by Farmer. 

   Spring deposits on lake bottoms often form at lower 
temperatures that do not deteriorate the organic material as much 
as a high temperature spring.  Microbes trapped in these deposits 
can be preserved for hundreds of millions of years, he said. 

   Lakes can also evaporate, leaving salt that entraps the cell 
walls and extracellular material of microbes.  However, salt tends 
to dissolve easily.  If a surface water cycle is active, its 
crustal residence time is short, Farmer said. 

   Farmer presented his research at the Geological Society Meeting 
of America in San Bernardino, Calif.  Farmer and his colleagues 
recently compiled a catalog that includes Mars exobiology sites.  
NASA will publish the catalog later this year.

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