The odd case of desert varnish
(above: An example of desert varnish from Lower Calf Creek Falls Trail in Utah. Photo Credit: Darren E. Logan)
One prime candidate for further study, Cleland suggests, is desert varnish: “There is no scientific consensus on how it is produced, despite the fact that geologists have extensively studied it; even Darwin found it puzzling.”
Desert varnish is a thin chemical and mineralogical coating on rocks in arid regions. Cleland says it bears an “uncanny morphological resemblance to stromatolites,” which are sedimentary structures produced over time by microbes like cyanobacteria.
Further, Cleland points out, varnish coatings are high in manganese and iron despite the fact that the rocks on which they are found are not. Bacteria and algae commonly produce manganese and iron as by-products during metabolism, but microbes (as we know them) are rarely found on the surface of desert varnish.
Again, Cleland emphasizes, this does not mean that “shadow microbes” (forms of life we do not perceive as such) exist now or ever existed. “The point is only that the objections commonly raised against them do not bear up well under scrutiny,” she writes.
In her office recently, Cleland reflected on people’s sometimes-visceral reaction to discussions of shadow microbes. “When I first started talking about it, people got mad,” she says.
In a report on alternative life issued last year, the National Research Council all but dismissed the possibility of shadow microbes on Earth. “There is no reason to believe, or even to suspect, that life arose on Earth more than once, or that it had biomolecular structures that differed greatly from those shared by the Terran life that we know.”
The NRC may not share Cleland’s thesis, she says, “But at least they’re talking about it.” Indeed, the NRC report later concedes that “as Cleland and Copley have recently discussed, it is conceivable that Earth harbors yet undiscovered forms of life that are not related by common ancestry to the life that we know, have quite different biochemistry, and may have been overlooked for precisely that reason.”
The NRC also argues that the search for life on other planets should account for the possibility that life on alien worlds may be, biologically speaking, weird.
As the NRC wrote, “Nothing would be more unfortunate than to expend considerable resources in the search for alien life and then not recognize it if it is encountered.”
In reaching that conclusion, the NRC relied, in part, on the difficulty in defining “life” from a single example. The authoritative group cited the work of Cleland.
She understands why the possibility of a shadow microbe on Earth is unsettling. “That fact that it might be in your rug upsets people.”
That is, of course, no reason to stop studying the rug.
In his book “Science, Society, and the Search for Life in the Universe,” Professor Jakosky makes a similar point: “We are exploring our solar system and trying to understand the origins of life here and beyond in order to satisfy a deeply embedded human curiosity about the world.”
Understanding the potential and actual distribution of life in the universe will, he says, help us comprehend our species, our society and our individual lives.
Jakosky concludes by quoting an unlikely source, the poet T.S. Eliot, who presciently but unintentionally summarized the rationale for astrobiology: “We shall not cease from exploration, and the end of all our exploring will be to arrive where we started and know the place for the first time.”
Elsewhere on the new-life beat…
The efforts described here represent only some of the work on the search for new life. University of Colorado students and faculty have joined this effort in several ways. For instance:
- CU students are controlling one of NASA's Kepler spacecraft to hunt down Earth-like planets in other solar systems. A team of 20 students and 16 professionals from CU-Boulder's Laboratory for Atmospheric and Space Physics is operate the spacecraft from the LASP Space Technology Building in the CU Research Park following Kepler's launch from Cape Canaveral, Fla. The Kepler mission is fueling growing excitement among space scientists in the wake of the discovery of more than 300 planets orbiting other stars in the past 15 years. Although most are gas giants the size of Jupiter or larger, the sensitive instruments aboard Kepler will target the identification, location and orbit of small, rocky planets roughly the size of Earth that may indicate possible havens for life.
- Stephen J. Mojzsis, associate professor of geological sciences at CU, is participating in the “Origins Symposium” next month at Arizona State University. He will join a discussion titled “How does life originate and how do we recognize it?” Among the panelists assembled for this event are cosmologist Stephen Hawking, genomic pioneer J. Craig Venter and evolutionary biologist Richard Dawkins.
CU’s Office of News Services contributed to this report
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