New geochemical data from the South African Agouron drill cores paint a clearer picture of oxygen distribution in the Late Archean marine environment! Rhenium and molybdenum abundances and sedimentary iron geochemistry in 2.6-2.5 Gyr old black shales indicate that photosynthetic production of oxygen by cyanobacteria was vigorous in the Late Archean surface ocean near the continents. Mildly oxygenated waters extended below the photic zone before giving way to anoxic deep and open oceans. Mass independent fractionation of S isotopes indicates that atmospheric oxygen abundances remained below 0.001% of the present atmospheric level. Our results show that substantial oxygen accumulation began along productive ocean margins more than 100 million years before the first significant increase in atmospheric oxygen concentrations. This research was a collaborative effort with Chris Reinhard and Timothy Lyons from the University of California (Riverside), Alan Jay Kaufman from the University of Maryland, and Simon Poulton from Newcastle University. The paper is now available in the September 2010 issue of Nature Geoscience.

FIGURE CAPTION: Simplified representation of the redox conditions along Late Archean ocean margins beneath a low-oxygen atmosphere (credit: Susan Selkirk). The orange cells in the inset figure are Synechococcus, a unicellular cyanobacterium only about 1 um in size (credit: Susanne Neuer/Amy Hansen). Organisms like Synechococcus were responsible for pumping oxygen into the environment 2.6-2.5 Gyr ago.

Uranium ore concentrates (UOCs) from around the world were measured for both ²³⁸U/²³⁵U and ²³⁵U/²³⁴U ratios.  These isotopic signatures can reveal the type of geologic environment in which the uranium was deposited (²³⁸U/²³⁵U), as well as the extent of modern water/rock interactions (²³⁵U/²³⁴U).  The pairing of these two systems on the same sample allows the a mine to develop a uranium isotope "fingerprint" which can be useful in cases of illicit smuggling of nulcear material.

Jennifer Glass has a new publication in Limnology & Oceanography entitled "Molybdenum-nitrogen colimitation in freshwater and coastal heterocystous cyanobacteria", coauthored with Anbar alum Felisa Wolfe-Simon, collaborator Jim Elser and Ariel Anbar. This work experimentally evaluates the sensitivity of several species of cyanobacteria to molybdenum and nitrogen limitation. Molybdenum (Mo) is a metal critical for nitrogen fixation, and the requirements for freshwater and salt water organisms might be expected to vary due to the more than five-fold Mo concentration decrease in freshwater compared to the ocean. Contrary to expectation, cyanobacteria from both environments were able to continue fixing nitrogen for more than a month even under low Mo conditions. Details of the rates of nitrogen fixation and chlorophyll content suggest that freshwater cyanobacteria were more robust in Mo-limited conditions due to gene expression of the Mo-storage protein mop.

An All Hands meeting of ASU's "Follow the Elements" Astrobiology group at ASU's Memorial Union on January 25-26th, 2010 brought together the many investigators on this grant from NASA's Astrobiology Institute. Two days of workshops, talks and poster sessions outlined the results already emerging from this exciting field of research, including Greg Brennecka's recent Science paper.

Other talks included The Stoichometry of LIfe - Lab, Field, Geology and Genomes (Jim Elser, lead); Astrophysical Constraints on the Elements of Life - ²⁶Al, Water, Supernovae (Frank Timmes, lead); and Habitability of Water-rich environments - Mars, Europa, Enceledus, Titan and KBOs (Mikhail Zolotov, lead).

Updates on NASA Missions included presentations from Phil Christensen (Mars), Paul Scowen (Astronomy), Ron Greeley (Europa) and Dante Lauretta (asteroids). An undergraduate outreach event on the evening of January 26th was lead by Steve Desch.

Greg Brennecka is lead author on a paper appearing in the January 22nd, 2010 issue of Science. Coauthored with Stefan Weyer, Meenakashi Wadhwa, Phil Janney, J. Zipfel and Ariel Anbar, this paper measures the ²³⁸U/²³⁵U ratio in meteoritic material. This ratio has been assumed to be invariant, and is a critical assumption when calculating the age of the Solar System by the lead-lead dating method. These results show that the ²³⁸U/²³⁵U variations seen in these samples could cause miscalculation of the Solar Sytems oldest solids by as much as five million years. Calcium-Aluminum-rich Inclusions (CAI's) of the Allende meteorite have variable ²³⁸U/²³⁵U ratios, and correlations with curium analogs of thorium and neodymium suggests the variability is caused by decay of ²⁴⁷Cm to ²³⁵U in the early Solar System. This exciting result was profiled in a Science Perspective article by J.N. Connely in the same issue.

Ariel is a coauthor on four papers in the journal Science that have emerged out of study of sediments in Western Australia deposited during the Late Archean, 2.5 billion years ago These papers all provide evidence of trace amounts of O2 in the environment before the transition to a generally oxidizing atmosphere. The latest paper is in the October 30th issue. You can read about some of the results here. This latest work is in conjunction with collaborator Tim Lyons at University of California, Riverside and is first-authored by UCR grad student Chris Reinhard. The paper studies iron speciation in black shales, and demonstrates that the early oxygenation of the Earth system was more nuanced and variable than previously thought.

This summer we bid a sad goodbye to postdoc Brian Majestic, visiting scientist Tsuyoshi Komiya and undergraduate Bryan Rolfe, and welcomed postdoc Amisha Poret-Peterson and lab technician Carina Arrua. Brian left us for a position at Northern Arizona University in the Department of Chemistry and Biochemistry, while Bryan has continued on to pursue a doctorate in Chemical Engineering at Cornell. He hopes to pursue the topic of his NSF fellowship proposal, nanofluidic batteries. Komiya returns to his position as an Associate Professor at the Tokyo Institute of Technology. Amisha joins us from the University of Louisville, where she worked Professor Martin Klotz on nitrification genes in methane-oxidizing bacteria. Carina comes to us with a Masters from the Universidad Nacional de Córdoba in Argentina, where she used multivariate statistics to authenticate wines from several regions in Argentina. She will be assisting users in the clean lab and with measurements on the quadrupole ICP-MS in the Keck lab. Gabi Montanez is still at ASU, but is focusing on completing her Master of Science in Engineering (MSE) program in the School of Mechanical, Aerospace, Chemical and Materials Engineering.

Jennifer Glass's project has been selected for the NASA Astrobiology Institute/APS Lewis and Clark Fund for Exploration and Field Research. Her project is entitled "Evaluation of Molybdenum Diagenesis in Sediments of Castle Lake, California". Read about the prize and all the winning projects.

At the first meeting of the Astrobiology seminar of the Fall 2009 semester, Everett Shock outlined the importance of the Yellowstone hot spring ecosystem and reviewed the sampling design for the recent successful 2009 field season. Steve Romaniello then described the purpose and methodology of the experiments to look at the rates of nitrogen cycle steps by spiking incubated experiments with 15N. Come join us at this cutting edge exploration of the science of astrobiology!

Ariel, Steve, Hilairy, Stan, Everett, Amisha, Tracy and Chris (among others!) returned from a successful field season collecting samples in the hot springs of Yellowstone. These extreme environments inform us about the limits of life and what life in other parts of the solar system and beyond might be like. In fact, fall semester 2009, there will be a seminar series, "Hydrothermal Ecosystems" to allow students (and faculty!) to gain a greater appreciation of the system dynamics. Co-led by Everett Shock and Jeff Dick, the organizational meeting for this course was Monday, August 24th at 4 pm in PS-H 460.

Jennifer Glass completed a successful field season at Castle Lake collecting porewater, sediment core and water column samples at this glacial molybdenum-poor lake.

"When do black shales tell molybdenum isotope tales?" Geology vol 37 no 6, p. 535-538, doi: 10.1130/G25186A.1 appears in June 2009. Molybdenum isotopes in ancient black shales have been used to tell us about the amount of oxygen in the world’s oceans in the past. Lighter isotopes preferentially go into oxic sediments, while sediments laid down in water columns with high sulfide reflect the isotopic composition of the water. By looking at two similar sequences of Devonian rocks (~380 million years old), Gordon et al. constrain what types of organic-rich sediments record the signal from ancient seas. The evidence is consistent with larger areas of the seafloor with low oxygen in the middle Devonian.

A paper, by Gwyn Gordon with co-authors Matt Rockman (New York University), Karl Turekian (Yale) and Jeff Over (SUNY at Geneseo), appears in the May issue of the American Journal of Science ("Osmium Isotopic Evidence Against an impact at the Frasnian-Famennian boundary", AJS v. 309, p.420-430; doi:10.2475/05.2009.03). This paper demonstrates conclusively that there could not have been a global meteorite impact immediately prior or during this mass extinction boundary - one of the five largest in Earth's history. The paper examines two sites: one in upstate New York and the other in France. The upstate New York sequence measured ten depths below, at and above the boundary and derived an isochron that is consistent with other measurements of the boundary's age. This is the first direct measurement of osmium isotopes at the F-F boundary; the initial 187Os/188Os value of 0.49 ±0.16 is consistent with other estimates of marine Os isotopes for this period and demonstrates no indication of significant extraterrestrial material. Samples at La Serre, France, have highly enriched Os concentrations of greater than 33 ppb - the highest published Os concentrations for this boundary and more than two orders of magnitude higher than average shale - but the 187Os/188Os is highly radiogenic and indicates no addition of significant meteoritic material.

Jennifer Glass' new article entitled, "Coevolution of metal availability and nitrogen assimilation in cyanobacteria and algae" is in press at Geobiology. It can be found at DOI: 10.1111/j.1472-4669.2009.00190.x. Coauthored with Felisa Wolfe-Simon and Ariel Anbar, this publication represents an important advance in our understanding of how the oxygenation of the early Earth was reflected in biological evolution.

Ariel's December 2008 publication in the Perspectives section of the December 5th issue of Science inspired a profile of his pioneering research in ASU's Research magazine. You can find the article here.

"Re-Os and Mo Isotope Systematics of Black Shales from the Middle Proterozoic Velkerri and Wollogorang Formations, McArthur Basin, Northern Australia" in Geochimica Cosmochimica Acta is now available here. Coauthored with Rob Creaser (at the University of Alberta), Gwyneth Gordon and Ariel Anbar, this paper represents an exciting combination of careful age dating with the Re-Os method and Mo isotopes for constraining the paleoredox of the ancient oceans at this time. Dr. Kendall is currently the only scientist implementing both isotope systems to closely link paleoredox to precise points in Earth history.

Ariel's article entitled "OCEANS: Elements and Evolution" appears in the December 5th issue of Science. The article can be found at DOI: 10.1126/science.1163100. It outlines how changes in elemental abundances in Earth's oceans on geological time scales are intimately linked to evolutionary processes.

A display about the W.M. Keck Foundation Laboratory for Environmental Biogeochemistry (aka KFLEB) is now on view from August 18th - October 18th in the Dean's office in the Foundation building. Examples of types of samples analyzed by our group are included.

Ph.D. students in the Anbar Lab Steve Romaniello and Jen Glass, along Cornell University professor Louis Derry, will be chairing an exciting session at the upcoming AGU meeting: PP13, Evolution of the Marine Nitrogen Cycle through Time. For more information, click here. Abstracts are here September 10, 2008 -- for abstract submission, click here.

Coffee, cotton and cannabis: Sr isotopes and the geolocation of botanical materials!

For the list of Isoscapes 2008 abstracts (Gwyn's is #47), click here.

To learn about the Isoscapes 2008 conference, click here