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NASA Develops Plan to Search for Martian Fossils
Headquarters, Washington, D.C. March 22, 1994
Ames Research Center, Mountain View, Calif.
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
"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
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.
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
"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,
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
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