How to Find Signs of Life on Mars

December 18, 2009 by Clara Moskowitz
On sandy beaches microbial mats composed of cyanobacteria form characteristic structures. The left column of this figure shows modern structures, the right column the fossil counterparts. Credit: Noffke, 2009, Earth Science Reviews

By studying the signatures of fossil life on Earth, geobiologists can get a clue of what to look for when hunting for extraterrestrial life on Mars.

Certain environments on Earth that host life are very similar to places on and other terrestrial planets, scientists have found. So if life can exist here, why not there?

Nora Noffke is a geobiologist at Old Dominion University in Norfolk, Virginia. She has found evidence of all over the world - in both modern and in coastal areas. Bacteria that grow on beach sand form microbial mats - organic layers that resemble carpets over the ground. Such carpets - composed of trillions of individual moving actively through the sand - leave characteristic traces in the beach deposits. We can study those traces in modern beaches of our Earth today. However, those bacterial traces also can become fossils that record ancient coast lines of the past. The oldest traces of such fossils date back to 3.2 billion years ago.

Noffke and her colleague Sherry Cady of Portland State University in Oregon recently wrote an article in the November 2009 issue of the Geological Society of America's journal, GSA Today, detailing how the melding of geology and biology can teach us about the environments most likely to host extraterrestrial life.

The microbes Noffke studies are simple organisms called that require no more than sunlight to grow. Organisms like this, which use the process of photosynthesis to convert sunlight to energy to live on, are called photoautotrophs.

"They can live basically anywhere," she said. "They can grow directly on pure sterile sand. They don’t need any soil. They gather all they need from the atmosphere and sunlight."

A microphotograph of cyanobacteria (blue-green algae) that photosynthesize carbon dioxide to produce oxygen. Credit: NASA

Cyanobacteria that colonize sand are pioneer organisms that help to pave the way for more complex plants to develop by creating usable nitrogen as a byproduct.

Since cyanobacteria have had such an easy time existing in austere environments on Earth, there's no reason they couldn't have lived on other planets, Noffke said. Earth's solar system neighbor, Mars, seems an especially good candidate because it is thought to have, or to have once had, liquid water.

"The likelihood that there were some kind of bacteria colonizing lakes or oceans on Mars is very high," Noffke said.

If it's so likely, why haven't we found evidence of life on Mars yet?

"It's just a matter of continuing to search," Noffke said. "It just takes time to hit the right spot, to be lucky to find something."

Noffke herself has travelled around the world looking for evidence of cyanobacteria in new and diverse locations both along modern coasts and in ancient rocks. Even on this planet with past and present life abundant, finding colonies of cyanobacteria can sometimes take time, she said.

"I went to South Africa," she said. "It took weeks until we found one little spot where we actually saw something in a rock. Even on Earth you have to search for a long time to find it. Bacteria are small, which we cannot say of a whole planet such as Mars."

Once you find them, the signs of cyanobacteria are unmistakable. The mat-like extent of the bacteria leaves a wrinkle pattern in the rock. The crinkle structure cannot be mimicked by anything else, and isn't easily mistaken for other processes, Noffke said.

Future explorers will have to look closely to detect fossil traces in the rocks of Mars. Opportunity rover found hematite “blueberries” scattered across the surface of this rock. Scientists think groundwater carrying dissolved iron percolated through the sandstone to form the tiny spheres. Image credit: NASA/JPL-Caltech/Cornell.

"If you'd really like to search for life elsewhere, that’s what to look for first," she said. "That’s the most dominant structure."

Noffke and other geobiologists help the search for life beyond Earth by compiling databases of the signals life leaves in its wake. Then if an intriguing pattern is ever found in Martian rock, for example, the structure can be compared with Earthly analogues, and statistical analysis can tell whether they are sufficiently similar to prove the structure was made by living things.

"We came up with a whole catalog of what we term biosignatures," Noffke said. "Those biosignatures are signals caused by life in an environment (past or present). Our biosignatures in the sand or sandstone are significant, simply because sand and sandstone is a very common deposit on Mars. We send our catalogue of fossil and modern biosignatures to NASA to provide the information what to look for."

By some analyses it seems like , or at least proof of its past existence, is a sure thing, just waiting to be discovered in the solar system. But scientists still don't know all of the necessary conditions for life, nor what the spark was that started life on Earth. Until we can answer those questions, the best hope for discovering whether there is life on another planet is to look for evidence of it in the rock record, Noffke said. Noffke’s catalogue of biosignatures should help future missions identify the signs of , if they are really there to be found.

Explore further: Cold case: Looking for life on Mars

Related Stories

Cold case: Looking for life on Mars

March 22, 2006

Evidence never dies in the popular TV show Cold Case. Nor do some traces of life disappear on Earth, Mars, or elsewhere. An international team of scientists, including researchers from the Carnegie Institution's Geophysical ...

Seeking Life's Shadow

October 1, 2009

They haven't yet figured out how to draw blood from stones, but a group of French researchers is offering new insight that could change how scientists search for signs of life in Martian rocks.

Evidence of ancient hot springs on Mars detailed

February 12, 2009

New Rochelle, NY, February 12, 2009 -Data from the Mars Reconnaissance Orbiter (MRO) suggest the discovery of ancient springs in the Vernal Crater, sites where life forms may have evolved on Mars, according to a report in ...

NASA images, White Sands features support a wetter Mars

December 7, 2006

NASA's announcement yesterday of evidence that water still flows on Mars, at least in brief spurts, demonstrates that the view of Mars as a very dry planet should be reevaluated, says Dawn Sumner, professor of geology at ...

Australia's ancient oceans: toxic and purple

October 6, 2005

Ancient oceans in Australia’s north were toxic seas of sulfur, supporting coloured bacteria that made the seas appear purple and unlike anything we know of in the Earth’s history, according to new ANU research.

Recommended for you

Major space mystery solved using data from student satellite

December 13, 2017

A 60-year-old mystery regarding the source of some energetic and potentially damaging particles in Earth's radiation belts is now solved using data from a shoebox-sized satellite built and operated by University of Colorado ...


Adjust slider to filter visible comments by rank

Display comments: newest first

not rated yet Dec 18, 2009
What ever came of the last Mars lab that was operating in the past year or two? I searched the NASA site and couldn't find anything about it and I can't remember the project name.
Surely NASA has finalized and reported the results of that mission by now.
1 / 5 (1) Dec 20, 2009
Phoenix. They had a hard time getting samples into the ovens, and then the Martian winter came and it ran out of power.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.