Geobiology: August 2011

The Department of Geology at Kansas State University invites applications for a full-time tenure-track position in Environmental Geobiology, at the rank of Assistant Professor. Compensation is based on the nine-month academic year, although two months summer salary may be negotiated for up to two years. A competitive startup package is available. The position will start no later than August 2012 and may begin earlier if mutually agreeable.

Review of applications will begin on September 15, 2011 and continue until the position is filled.

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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).

In recent years, scientists have found evidence that a 'near complete' biological nitrogen cycle existed in the oceans during the late Archean to early Proterozoic (from 2.5 to 2 billion years ago). Modern bacteria use an enzyme called nitrogenase to cycle nitrogen from one form to another. This enzyme is dependent on the presence of metallic elements like iron (Fe), vanadium (V) and, most often, molybdenum (Mo). However, ancient oceans didn't contain much molybdenum. Could Fe-nitrogenase or V-nitrogenase have played a larger role in the archaean oceans than they do today? To answer this question, a team of researchers at NAI's Montana State University and Arizona State University teams studied the phylogenetic relationships between the proteins that allow nitrogenase to interact with each of the three elements. Their results suggest that the protein (known as Nif protein) actually developed in methanogenic microorganisms, and was then incorporated into bacteria by lateral gene transfer around 1.5-2.2 billion years ago. Ultimately, if Mo-nitrogenase originated under anoxic conditions in the Archaean, it would have likely happened in an environment where both methanogens and bacteria coexisted, and where molybdenum was present for at least part of the time.

The emergence of enzymes like Mo-nitrogenase was a significant step in the evolution of life, and had powerful repercussions for planet Earth and its biosphere as a whole. This research can help answer important questions about the environmental conditions that were present on the early Earth, and the interactions that occurred between life and the ancient planet.

The results were published in the May edition of the journal Geobiology

The record of Earth's sulfur cycle preserved in sedimentary rocks is commonly used to track the evolution of microbial sulfur metabolisms and levels of atmospheric oxygen throughout geologic history. Sulfur isotope evidence suggests the Earth's atmospheric oxygen appeared about 2.4 billion years ago, but its level remained rather low until about 650 million years ago.

New studies by NASA Astrobiology Institute scientists have questioned the extent to which the record of the sulfur cycle reflects the oxygenation. The team has demonstrated that a laboratory culture of a marine sulfate-reducing bacterium can produce sulfur isotope signatures beyond the threshold previously used to define the boundaries for different sulfur metabolisms. This finding suggests that oxygenation is not the only mechanism that can explain similar signatures in modern and ancient sediments. The team's paper was published in the July 1 issue of Science.