Paleobiology & Biosignatures: September 2011

The Institute for Astronomy (IfA) invites applications for a Postdoctoral Fellowship with interests in the origin of Earth's water to work with the University of Hawai'i's NASA Astrobiology Institute lead team (see The UH lead team maintains an innovative and multi-disciplinary research environment linking astronomical, biological, microbiological, chemical, and geological sciences to investigate the origin, history, distribution and role of water as it relates to life in the universe. The program centers around interactions with an interdisciplinary group of postdoctoral fellows. We have a particular need for an individual interested in the origin of Earth's water, and, by analogy, terrestrial planetary volatiles. The work involves geological field work to sample primitive, deep-mantle-plume materials, preparation of samples of melt inclusions in olivines from Hawaiian and Icelandic basalts for isotopic measurements using the petrographic microscope, scanning electron microscope, and electron microprobe, and measurements of D/H ratios and hydrogen abundances in the melt inclusions using the UH Cameca ims 1280 ion microprobe. The Fellowship is for one year and may be renewable up to a total of 3 years assuming satisfactory progress and continued availability of funds. The fellow will receive a stipend of approximately $5,000 per month, a small relocation allowance and basic research costs.

Molecular Fossil Records

Among the various geochemical proxies for the presence of molecular oxygen in the environment, molecular fossils offer a unique record of oxygen where it was first produced and consumed by biology: in sunlit aquatic habitats. Steroid biosynthesis requires molecular oxygen, making the study of sterane molecular fossils important in reconstructing early environmental conditions. In a new study, NAI-funded scientists and their colleagues present evidence that microaerobic marine environments where steroid biosynthesis was possible could have been widespread and persistent for long periods of time prior to the earliest evidence for atmospheric oxygen. Their study is published in a recent issue of PNAS.

Source: NAI newsletter

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.

Cycling Nitrogen in Ancient Oceans

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

Searching for Extrasolar Biosignatures

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.