1. MOTIVATION & OVERVIEW At its surface, Earth is an oxygenated world. Molecular oxygen (O2), the second-most abundant gas in the atmosphere, largely determines Earths surface mineralogy (Hazen et al., 2008; Sverjensky and Lee, 2010), and makes metazoan life possible (Catling et al., 2005; Payne et al., 2011). In contrast, oxygen is never present as O2 deep beneath the Earths surface, which is a substantially more reducing environment. In Earths core, oxygen is highly depleted, possibly reflecting an early phase of the accretion process (Wood 2011; Huang et al. 2011). The redox contrast between the surface and deep Earth is extreme. This fundamental aspect of the Earth system is poorly understood (Canfield, 2005). We know that biology is essential to O2 production, converting solar energy into redox disequilibrium, but we do not know when, how, and why the system arrived at its present state. In short, we do not understand the geochemical cycling and dynamics of the most abundant element on the planet. The problem is difficult because the geochemical cycles of oxygen and other redox-sensitive elements span vast spatial and temporal scales. Interactions between the oxidized surface and the reduced deep Earth dominate on timescales of 108 - 109 years. Tectonics, weathering, and sedimentary basin processes are important on timescales of 105 - 108 years. On shorter timescales, the production and consumption of O2 are affected by complex relationships between biological productivity, nutrient cycling, atmospheric chemistry, and carbon burial. Any comprehensive model of Earths redox budget must couple these disparate processes that are usually studied and taught in isolation. To meet this challenge, we propose a FESD project of multi-disciplinary research, training, and education outreach, bridging the deep time and deep Earth communities. The project centers on the Great Oxidation Event (GOE), the large, secular rise of O2 in the atmosphere 2.45 - 2.32 Ga that initiated a prolonged and complex transition to an oxygenated ocean over the subsequent 2 billion years (e.g., Holland, 2002; Canfield, 2005). The cause of this transition is surprisingly unsettled. Our goal is to solve this mystery and to apply the lessons learned to more generally understand the dynamics of environmental oxygenation, including the Neoproterozoic Oxygenation Event (NOE) associated with the rise of metazoa (Shields-Zhou and Och, 2011), and later changes in environmental redox. This research is poised for a major advance because of dramatic recent advances in our knowledge of what happened during the GOE and its aftermath. A wealth of data has led to a proliferation of hypotheses that are ripe for testing by synthesizing existing information with carefully targeted new datasets and models. A team-based interdisciplinary approach is required because many of these hypotheses invoke connections between the surface and deep Earth, and so cannot be tested without collaboration between research communities. The project is potentially transformative because it recognizes that a fundamental understanding of the O2 problem requires a novel integration of geobiological, geochemical, and geophysical principles and observations. Our goal to understand how the interconnectedness of these processes leads to simple consequences such as an oxygenated atmosphere represents an attempt to go beyond biocentric ideas views such as the Gaia hypothesis (Lovelock, 1979) and theories that attribute Earth history purely to the evolution of plate tectonics and other physical processes. If successful, our project will spark the ascendance of a holistic perspective that integrates all facets of the Earth system to understand its history and future.
|Effective start/end date||9/1/13 → 8/31/20|
- National Science Foundation (NSF): $4,845,000.00