2012 Annual Science Report
Arizona State University Reporting | SEP 2011 – AUG 2012
The “Follow the Elements” NAI Team at ASU carries out research, education and outreach activities centered on the chemical elements of life. Our activities are motivated by a simple observation: that life-as-we-know-it uses a non-random selection of the chemical elements. This observation prompts many questions:
*What are the rules that govern the selection of these “bioessential” elements?
*How might these elements differ in extreme environments on Earth or beyond?
*How common are the bioessential elements in the extraterrestrial environments that might harbor life?
*How are the distributions of these elements in the cosmos shaped by astrophysical processes?
The answers to these questions will shape the future exploration for life on other worlds. We seek to answer these questions through laboratory, field and computational research, and use them as the basis for much of our education and outreach. To this end, the project is organized around three major research themes: The Stoichiometry of Life; The Habitability of Water-Rich Environments; and Astrophysical Controls on the Elements of Life. We pursue each theme by way of a number of focused research tasks.
During Year 4 of our program, the Astrobiology Program at Arizona State University continued to advance most of the major research tasks described in our CAN5 proposal, and other new projects. Some of these projects reached very significant conclusions, as summarized below. These efforts resulted in ~ 60 publications that appeared in print during the reporting period. These included several publications in high-profile journals. Collectively, this ongoing research advanced our goal of integrating life science, geoscience, planetary science and astrophysics to understand how the distribution of chemical elements shapes the distribution of life in space and time, and to guide the search for life beyond Earth. This work is comprehensively described in the main report. Key outcomes are highlighted here.
1. The Stoichiometry of Life
This theme includes several tasks aimed at elucidating relationships between the availability of bioessential elements and prokaryotic ecosystems. These tasks involved: experimental studies in the laboratory (Task 1); field studies and associated laboratory analyses at Yellowstone National Park (YNP) and Cuatro Cienegas (CC), Mexico (Tasks 2a and b respectively); evolutionary studies in the geologic and genomic records (Tasks 3a and 3b, respectively); and a coupled modeling-experimental project to understand the connections between biogeochemical cycles of carbon, oxygen and bioessential nutrient elements in prokaryote-dominated oceans (Task 4).
As in Year 3, in this project year Task 1 projects melded somewhat with our Task 2 projects as samples gathered in the field were intensively studied in the laboratory. Notable outcomes from Tasks 1 and 2 included:
*Significant progress in the physical separation of cells from non-biological materials collected from hotsprings at YNP, for subsequent analysis of C, N, P and other elements. Initial findings are that C:N:P of cells from photoautotropic and chemoautotrophic communities are both similar to the Redfield ratios, although the communities differed in their patterns of P and Mn enrichment. The implications are being investigated. In parallel, we initiated an X-ray microanalysis investigation of C, N and P in single cells, using electron microscopy.
*Ongoing advances in our work reconstructing nitrogen and carbon metabolism in hotsprings at YNP. These efforts use 15N and 14C tracers to follow these elements. A highlight from NanoSIMS analyses of samples from incubation experiments is that only a portion of the microbial community is responsible for most of the N assimilation, and that N uptake was highly variable among cells.
*Development and deployment of MEMS temperature sensor arrays and conductivity sensors in YNP, targeting the transition zones between different microbial communities. A similar set of sensors was deployed at a privately owned hotspring in Gerlach, NV, but configured for long-term monitoring via satellite communication. These studies investigate the dynamics of the temperature-dependent “fringe” between photosynthetic and chemosynthetic communities.
*Initiation of a new study of metabolomics of the cyanobacterium Synechocystis sp. PCC6803 under different nutrient conditions in the laboratory, in collaboration with Autonomous University of Barcelona.
*Initiation of a new study of microbial colonization of floating pumice rafts, taking advantage of the massive eruption of the Puyehue / Cordon Caulle volcano in Argentina.
*Publication of multiple papers tied to the genomics and biological stoichiometry of the CC field site (a special issue of Astrobiology on this site was published in mid-2012), led by ASU Co-I Jim Elser and collaborator Valeria Souza (National Autonomous University of Mexico).
In Task 3a, the specific Proterozoic basin work pursued in prior years shifted from data collection to manuscript preparation, and so we broadened our efforts to records of Proterozoic ocean redox evolution more broadly. One key highlight, which began to emerge in Year 3, was the generation of yet more evidence that mid-Proterozoic oceans, once thought to be dominated by sulfidic deep seas, were characterized by low O2 and elevated iron abundances – so-called “ferruginous” conditions. In Year 4, this new view was summarized by Lyons and Reinhard (2011), with key insights coming from Planavsky et al. (2011) and Li et al. (2012). Our work suggests that prevailing ocean redox during the mid-Proterozoic and coupled nutrient limitations may have throttled the proliferation of prokaryotic life, the early rise of eukaryotes, and ultimately the first appearance of animals—and, in the process, the burial of organic matter and the further rise of oxygen.
We also saw the culmination in publications of efforts to develop and apply new paleoredox proxies, notable Cr, Se and U isotopes (respectively, Konhauser et al., 2011; Mitchell et al., 2012; Brennecka et al., 2011), as well as several studies to calibrate and test the more established Fe and Mo isotope proxies.
Task 3b advanced a number of new techniques for interrogating evolutionary mechanisms in modern environments as a way to understand the ancient genomic record, and further resolved how and when these events changed the evolutionary trajectory of early life on Earth.
Task 4 completed a set of pilot experiments validating an approach to characterize and quantify the production of extopolymeric substances (EPS) by the cyanobacterium Synechococcus sp. WH8102 and demonstrating that these materials lead to formation of sinking aggregates that play a role in carbon export from the surface oceans even if they are bacterially dominated.
2. The Habitability of Water-Rich Environments
This goal of this theme is to improve our ability to infer the availability of bioessential elements in aqueous environments on Mars, in the outer Solar System, and on water-rich exoplanets. It includes tasks involving: Improving computational codes to model water-rock interactions (Task 1); application of modern geodynamics codes to ice dynamics on Europa and other icy bodies (Task 2); integration of these and other computational models with observational data to better assess the habitability Europa (Task 3), Mars (Task 4), other small icy bodies (Task 5), and postulated extrasolar “waterworlds” (Task 6).
Work along these tasks continued to advance. Notable highlights included: the development and application of a novel thermodynamic model that can be used to predict phase equilibria on Saturn’s moon Titan (Task 1); preliminary findings, via geodynamic modeling, of significant mass transfer from ocean to surface during ice convection on Europa (Task 2); new constraints from thermochemical models about the composition of Europa’s oceans (Task 3); model-based inferences of strong acidic weathering on the surface of Mars (Task 4); and investigations of crustal overturn on Kuiper Belt Objects (Task 5).
The most exciting development in this theme was the landing of the Mars Science Laboratory (Curiosity), which involved Co-I Jack Farmer and many other members of the “Follow the Elements” astrobiology community.
3. Astrophysical Controls on the Elements of Life
This theme aims to elucidate the influence of supernovae and other nucleosynthetic processes on the formation of solar systems, their composition and evolution. The theme includes tasks involving: High-precision isotopic studies of meteorites to quantify the timescales of the injection of supernova-derived materials (Task 1); computational modeling of the physical and chemical evolution of massive stars (Task 2); quantification of the injection of supernova ejecta to star-forming molecular clouds (Task 3) and protoplanetary disks (Task 4); modeling the chemical evolution of star-forming regions (Task 5); determining what elements might be used as observational proxies in stellar spectra for elements and isotopes not amenable to direct observation (Task 6); and incorporate element abundance data in the “HabCat” of nearby stars that could support life (Task 7).
Notable highlights in the project year included the development of a new approach to look for FUN inclusions in meteorites, which will help constrain the timing of injection of 26Al and other elements into the early Solar System (Task 1); discovery that variation in element abundance ratios observed in nearby stars have a substantial effect on the evolution of habitable zones around stars – the effect of the O/Fe ratio is particularly significant (Task 2); research showing with high confidence that supernova material will mix into nearby molecular clouds, so that all stars forming late (> 4 Myr) into the lifetime of a massive cluster will be contaminated with supernova material at a mass fraction ~ 10-4 – exactly the shift needed to explain the abundances of short-lived radio-nuclides like 26Al (Task 3); improved modeling of how radionuclides injected by a supernova into a protoplanetary disk might subsequently be mixed (Task 4); new modeling work on the transition from primordial star formation to formation of stars enriched in heavy elements (Task 5); the integration of stellar element abundance data with models of planetary interior composition and dynamics to model the thermal evolution of exoplanets (Task 6); and completion of the first complete database of bioessential elements for the stars closest to the Sun (Task 7).
Education and Public Outreach
EPO activities centered on:
Continued development of media-rich, immersive “virtual field trips” (VFT), mostly collaborative with the Australian Centre for Astrobiology and the NAI’s MIT team. The initial Ediacara (Flinders) and Shark Bay VFTs reached a high state of maturity, were converted to HTML5, and experiments were initiated to integrate an adaptive e-learning platform into these experiences. Additional VFTs were initiated with other support. VFTs can be seen at: http://vft.asu.edu.
The first two offerings of the fully online version of the general science class, Habitable Worlds, occurred in Fall 2011 and Spring 2012, to 300 ASU undergraduates. The course successfully incorporated several innovative technologies (including VFTs). Student surveys revealed solid statistical success and extremely positive anecdotal responses.
Support of the 2nd annual Teacher Leadership Academy (TLA) in Earth and Space Sciences organized by the Triad Project, an educational collaborative of the American Geosciences Institute (AGI), the School of Earth and Space Exploration at ASU, and NASA Goddard Space Flight Center. The TLA and its ancillary activities were funded by NASA Goddard Space Flight Center through a K-12 Cooperative Agreement with AGI and ASU. PI Anbar and Co-PI Semken are also Triad Project Co-PIs, and this enabled considerable cross-pollination between NAI science and Triad teacher professional development activities. Both Semken and Anbar were facilitators and presenters at the TLA.
These activities reached a variety of constituencies, including K-12 children and educators, college students, and the public at large.
As in past years, the ASU Team helped build the astrobiology community in a variety of ways, not all of which are captured in the standard reporting framework. Notably, on Feb. 27, 2012, we sponsored a Workshop Without Walls, “What Don’t We Know About Intelligence”, organized by Lori Marino and Kathryn Denning.