Research Summary for Previous Grant
How could we determine whether life did or could have existed? State-of-the-art techniques currently focus on organic molecules which may have altered over time; however, minerals can preserve information on the presence of life on the early Earth or elsewhere in the solar system. We propose to investigate the signatures and environments of life with a comprehensive, multidisciplinary program centered on chemical and isotopic biosignatures. Our work will touch on issues ranging from extraterrestrial delivery of the organic inventory required for life to development of instrumentation for remote in situ isotopic measurements on other planetary bodies. In addition, we propose an extensive experimental and computational program aimed at understanding the chemical and isotopic fingerprints left by life in three key mineral groups: sulfates, carbonates, and oxides. This work will develop the critical interpretive framework required to distinguish biologic from abiologic origins and constrain paleoenvironments of formation. Finally, we will test the biosignatures we develop through studies of natural terrestrial systems, ranging from modern field sites to 3.8 billion year old rocks.
We propose four investigations:
1. The inventory of organics in a planetary body – acquisition and modification during biogenic and abiogenic processes: To understand if life has affected a system, logically we begin with delivery of organic material to a planetary body early in its history. We seek to understand the chemical composition and isotopic fractionation of extraterrestrial organic matter that may represent the major carbon source for life’s origin on Earth and possibly Mars. In addition, we will study how to distinguish between abiogenic and biogenic carbonaceous material. Because long-term exposure to severe environments (temperature, UV-radiation, etc.) may change the nature of organics, we will test their survival in simulated planetary environments to determine the most plausible inventory of organics to be targeted by future space mission. Details on Investigation 1.
2. Development of biosignatures, paleoenvironmental proxies, and pathway tracers for aqueous-mineral systems: Robust biosignatures can only be developed though extensive experimental and computational work investigating abiologic and biologic formation pathways that may produce a proxy for life. We plan to focus on three mineral groups that are critical to astrobiology: sulfates, carbonates, and iron oxides. We will study the influence of microbial catalysis and abiological effects on O, S, Ca, Mg, and Fe isotopes during pyrite oxidation. The biotic and abiotic origins of mixed cation carbonate compositions will also be investigated, focusing on formation mechanisms and Ca, Mg, Fe, C, and O isotope variations. We will address key issues of iron oxide mineral genesis, including studies of the biologic and abiologic O and Fe isotope fractionations that occurr during oxidation of Fe2+. This investigation forms almost half of our research effort. Details on Investigation 2.
3. Testing covariations of biosignatures and paleoenvironmental indicators in natural terrestrial systems: Successful detection of life and its environments on other planetary bodies will only be possible if the methods used have been rigorously validated experimentally (Investigation 2), as well as field tested. We will test models for S and Fe oxidation in a modern environment, Rio Tinto, Spain, and determine the formation pathways of Fe, Ca, and Mg sulfates in such systems and their isotopic fingerprints. Another goal is to determine the relative roles of abiologic and biologic processes that formed iron oxide concretions in the Navajo Sandstone, an analog for iron concretions discovered on Meridiani Planum (Mars). We will investigate the origin of ferric iron oxides in the early Earth (3.8-2.5 b.y. ago) paleo-weathering horizons and oolitic banded iron formations (BIFs), and the evolution of sulfate- and iron-reducing bacteria in early Archean sedimentary sulfides and magnetite deposits. We will determine the genesis of early Archean (3.5 Ga) chert layers that contain low-C13/C12 carbon. Finally, we will investigate the oxidative pathways involved in ferric iron oxide formation in key BIFs that formed between 3.8 and 2.5 b.y. ago, as well as determine the role of Fe(III)-reducing bacteria in formation of magnetite and siderite in BIFs. Details on Investigation 3.
4. Development of in situ instrumentation to detect isotopic biosignatures on planetary missions: The ultimate goal of our biosignature studies is in situ measurement of the isotopic compositions of organic matter, minerals, and rocks on another planetary body. In the absence of sample return, sending high-precision mass spectrometers to make measurements that are analogous to those involved in Investigations 1, 2, and 3 above is our best chance of finding life elsewhere in the universe. This investigation dovetails with on-going instrumentation development at JPL, adding the critical components of sample introduction and calibration with conventional mass spectrometers. We will develop methods to introduce bulk samples into a JPL-developed miniature mass spectrometer (MMS) for complete isotopic analysis of H, C, O, S, Fe, Ca, and Mg in iron oxide, carbonate, and sulfate minerals. We will test the accuracy and precision of isotope analyses using the MMS for isotopic analysis against conventional instruments. Details on Investigation 4.