With the new award, University of Wisconsin-Madison scientists and their collaborators from the University of Georgia and the Jet Propulsion Laboratory (JPL) will become a key part of NASA's Astrobiology Institute.

"The long-term goal is to understand when life began on Earth, what are the criteria for determining that life existed on another planetary body," says Clark Johnson, the UW-Madison professor of geology and geophysics leading the new effort. "What we're looking for is the signature of past life as preserved in minerals."

If life existed elsewhere in our solar system or beyond, odds are it would have been single-celled organisms such as bacteria, which can leave a chemical trail preserved in stone. Such is the case with microbes on Earth. Scientists have developed a bevy of techniques to read those chemical signatures to understand something about life that existed on Earth hundreds of millions or even billions of years ago.

Earth, in fact, will be the laboratory for the new initiative as researchers seek to refine their understanding of the chemical impressions left by ancient bacteria and other microorganisms. Such a baseline will give scientists an interpretive framework for analyzing samples from Mars and other places beyond our planet that may have once harbored life.

Such context was lacking with the Allan Hills meteorite, a suspected piece of Mars found in Antarctica and theorized to be one of the oldest relics of our solar system at 4.5 billion years old. The meteorite made news in 1996 with the publication of a paper suggesting that tiny features in the rock might be artifacts of ancient Martian life.

That evidence, it turns out, is now discounted by most scientists. Thus, any future sample purported to harbor evidence of extraterrestrial life will be the subject of intense scientific scrutiny. "The bar is really high," says Johnson. "The (scientific) community is not going to believe it unless the interpretive framework behind it is fully developed."

To help achieve that, Johnson's group plans an isotopic approach as a way to ferret out the signatures of life from rocks that may be hundreds of millions or billions of years old. Most elements have different masses called isotopes, and very subtle changes can occur during biological reactions.

"Geologists are good at going back in time, and we will explore the isotopes in very ancient rocks," Johnson explains.

The allure of chemical isotopes as biosignatures, Johnson says, resides not only in their ability to identify the chemical fossils of past life, but also in their great durability.

He explains that any sample will have a complicated history and may have endured many changes over long periods of time. For example, minerals from another planet may have been exposed to large doses of ultraviolet radiation for billions of years, or geologic processes that can potentially change their composition. But the isotopic makeup of elements that were cycled by living creatures, Johnson notes, tend to resist such change.

His group will first compile an inventory of organic materials such as carbon, and in simulated planetary environments, test their survivability to assemble a plausible inventory of things to look for on another planet.

"We'll look for terrestrial analogs that we can really pull apart," says Johnson.

In recent years, scientists have found numerous Earthbound microbes that live in extremely hot and chemically forbidding environments, and it has been long known that microbial life can live off of and process elements such as iron. Knowing the kinds of signatures they leave behind will be a big help when samples from other planets become the subject of scientific scrutiny.

The new project, Johnson hopes, will exert influence on future NASA missions. Ultimately, his group will help with the development of a miniature mass spectrometer and other instruments that could be deployed by a probe to search for signs of past life on Mars or other planets.

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