Biosignatures & Paleobiology: August 2011

Fossils are essential to our understanding of the history and origins of complex life. New work from NAI's MIT and Penn State teams describes exquisitely preserved microfossils from mid-Neoproterozoic (811-717 million years old) rocks of the Fifteenmile Group, Yukon. These fossils are interpreted as biomineralized plates that covered the surface of a single-celled alga.

Their findings suggest that the minerals used by the ancient marine organisms have changed through time, perhaps linked to changing ocean chemistry. While the relationship of these fossils to modern organisms is difficult to determine, the researchers argue that it's likely that these unique fossils are the plates of an organism most closely related to green algae. Their paper appears online in Geology.

Ancient rocks are shedding new light on the timeline for life's emergence on Earth. The rocks from the Nuvvuagittuq Supracrustal Belt in Quebec, Canada, are believed to be some of the oldest on Earth. They contain carbon-based minerals that had been interpreted as evidence of the Earth's early biosphere, however, new research tells a different story. By applying cutting-edge technology to the rock samples, a team of scientists have revealed that the carbon minerals found in the rocks may be much younger than the rocks themselves.

"The characteristics of the poorly crystalline graphite within the samples are not consistent with the metamorphic history of the rock," said co-author Dominic Papineau in a news release from Boston College. "The carbon in the graphite is not as old as the rock. That can only ring a bell and require us to ask if we need to reconsider earlier studies."

The results were reported in the May 15, 2011 edition of the journal Nature Geoscience. Funding organizations for this work included the NASA Exobiology and Evolutionary Biology Program (Exo/Evo), the NASA Astrobiology Institute (NAI), the W.M. Keck Foundation, the Geophysical Laboratory of the Carnegie Institution of Washington, Carnegie of Canada, the Naval Research Laboratory, the NRC Research Associateship Program, Boston College, and the Fond Quebecois pour la recherche sur la nature et les technologies (FQRNT).

Researchers supported in part by the NASA Astrobiology Institute and the NASA Exobiology & Evolutionary Biology program have used computer models to study the potential of organic sulfur compounds to be biosignatures in exoplanetary atmospheres. The results indicate that the most detectable feature involves levels of ethane that are higher than expected based on a target planet's methane concentration. These detection techniques will be particularly useful for finding life on planets similar to the early Earth, that do have life but do not have atmospheric oxygen or ozone, two major biosignature gases. The team suggests that a mission that can detect the ethane and methane in exoplanet atmospheres could find life on such planets, thereby increasing our chances of finding a habitable world outside our solar system.

The study was recently published in the journal Astrobiology and is now available online.