Bacteria or Boulders? Methane and Life on Mars

By Fazale R. Rana, Ph.D.

During the summer of 2005, Paramount Pictures released a remake of H.G. Wells' War of the Worlds, a story about a Martian invasion of Earth. The real "invasion," however, has been occurring in reverse: it's NASA and ESA (European Space Agency) scientists who have been probing Mars. These two space agencies have dispatched orbiters and rovers to the red planet at a frantic pace in an attempt to find any evidence for Martian life.

Astrobiologists and origin-of-life researchers consider the discovery of indigenous life on Mars as a powerful way to confirm the naturalistic, evolutionary paradigm. They also look to Mars as a potential origin-of-life site, because the gathering evidence makes life's naturalistic origin on Earth increasingly unlikely. If life did not arise by natural means on Earth, they reason, perhaps it originated on Mars and was subsequently transferred to Earth about 3.8 billion years ago.[1]

Recently, astrobiologists found the possible smoking gun for Martian life: methane in the atmosphere (at 10 parts per billion).[2] Why methane? On Earth, atmospheric methane comes primarily from methanogens, bacteria-life!-that produce methane as a metabolic by-product. Therefore, astrobiologists reason that Martian methane, too, comes from microbes.

Methane has a short residence time in the Martian atmosphere (about 350 years) due to its photolytic breakdown by the Sun's UV radiation. This means that for this gas to exist in the atmosphere of Mars there must be ongoing methane production. Scientists estimate that it would take 20 tons of methanogens to maintain the atmospheric level of methane at 10 parts per billion. Does the discovery of methane indicate that methanogens (life) will follow?

Other scientists say no. They are not so quick to accept atmospheric methane as a life signature on Mars. Geologists point out that methane can be produced through nonbiological, geochemical pathways. For example, methane can form when hydrogen reacts with carbon dioxide. Hydrogen is readily generated when water reacts with the minerals olivine and pyroxene at the low temperatures and high pressures likely to exist within the Martian crust.[3]

Recently, two geologists from Dartmouth demonstrated that the resources (water, carbon dioxide, and olivine) needed to geochemically produce methane existed on Mars in the past, and may well exist today. They also determined that the olivine-mediated production of methane would be thermodynamically and kinetically favorable within the Martian crust.[4] Astrobiologists need only to detect serpentine (the mineral by-product of the reaction between olivine and water) to confirm this explanation for Martian methane. Rather than life-confirming methanogens, it seems that boring rocks may be responsible for Martian methane.

In the original release of War of the Worlds, the invading Martians were done in by disease-causing bacteria found on Earth. In the real life invasion of Mars, the scientific marauders in search of Martian microbial life appear to have been thwarted by methane-producing rocks.

References:

[1] Fazale Rana and Hugh Ross, Origins of Life: Biblical and Evolutionary Models Face Off (Colorado Springs, CO: NavPress, 2004).

[2] Mark Peplow, "Martian Methane Hints at Oases of Life," news@nature.com (September 21, 2004) http://www.nature.com/news/2004/040920/pf/040920-5_pf.html, accessed September 12, 2005.

[3] Mark Peplow, "Martian Methane Could Come from Rocks," news@nature.com (June 2, 2005) http://www.nature.com/news/2005/050531/pf/050531-10_pf.html, accessed September 12, 2005.

[4] Christopher Oze and Mukul Sharma, "Have Olivine, Will Gas: Serpentinization and the Abiogenic Production of Methane on Mars," Geophysical Research Letters 32 (2005): L10203-L10206, http://www.agu.org/pubs/crossref/2005/2005GL022691.shtml.