A5011371408- Paleontology and Stratigraphy of Fossils
- Geology and Paleoclimatology Research
- Isotope Analysis in Ecology
- Geochemistry and Elemental Analysis
- Geological and Geochemical Analysis
- Methane Hydrates and Related Phenomena
- Marine and environmental studies
- Astro and Planetary Science
- High-pressure geophysics and materials
- Selenium in Biological Systems
- Radioactive element chemistry and processing
- Hydrocarbon exploration and reservoir analysis
- earthquake and tectonic studies
- Marine Biology and Ecology Research
- Geochemistry and Geologic Mapping
- Botany and Geology in Latin America and Caribbean
- Marine and coastal ecosystems
- Geological and Geophysical Studies
- Atmospheric and Environmental Gas Dynamics
- Ocean Acidification Effects and Responses
- Evolution and Paleontology Studies
- Paleopathology and ancient diseases
- Oceanographic and Atmospheric Processes
- Climate change and permafrost
- Pacific and Southeast Asian Studies
California Institute of Technology
2020-2025
Duke University
2023-2024
Earth and Space Research
2016-2023
University of Washington
2016-2023
NASA Exoplanet Science Institute
2019-2021
Planetary Science Institute
2021
Seattle University
2021
NASA Astrobiology Institute
2016-2018
The scarcity of oxidants in the ancient oceans may have inhibited phosphorus recycling, stifling growth biosphere.
Significance Oxygen is essential for eukaryotic life. The geologic record of early Earth contains abundant evidence low oxygen levels, and accordingly, a lack eukaryote fossils. rise to near-modern levels at the end Proterozoic Era thus often cited as trigger evolutionary radiation complex life forms this same time. Here we present selenium geochemical data that indicate an expansion suboxic (>0.4 μM O 2 ) habitats in shallow oceans between 2.32 2.1 Ga––more than one billion years before...
Nitrogen is a major nutrient for all life on Earth and could plausibly play similar role in extraterrestrial biospheres. The reservoir of nitrogen at Earth's surface atmospheric N2, but recent studies have proposed that the size this may fluctuated significantly over course history with particularly low levels Neoarchean - presumably as result biological activity. We used biogeochemical box model to test which conditions are necessary cause large swings N2 pressure. Parameters our...
Significance Understanding how and when Earth’s surface became oxygenated is essential for understanding its biogeochemical evolution. Incipient oxygenation of environments before the Great Oxidation Event (GOE; ∼2.4 Ga) has been well-documented, but nature these redox changes, whether protracted or transient, poorly understood. We present nitrogen isotope ratios, selenium abundances, ratios from Jeerinah Formation (∼2.66 Ga; Fortescue Group, Western Australia) that represent ( i )...
Earth's early atmosphere witnessed multiple transient episodes of oxygenation before the Great Oxidation Event 2.4 billion years ago (Ga) [e.g., A. D. Anbar et al., Science 317, 1903-1906 (2007); M. C. Koehler, R. Buick, E. Barley, Precambrian Res. 320, 281-290 (2019)], but triggers for these short-lived events are so far unknown. Here, we use mercury (Hg) abundance and stable isotope composition to investigate atmospheric evolution its driving mechanisms across well-studied "whiff" O2...
Geobiology explores how Earth's system has changed over the course of geologic history and living organisms on this planet are impacted by or indeed causing these changes. For decades, geologists, paleontologists, geochemists have generated data to investigate topics. Foundational efforts in sedimentary geochemistry utilized spreadsheets for storage analysis, suitable several thousand samples, but not practical scalable larger, more complex datasets. As results accumulated, researchers...
Abstract Abundant geologic evidence shows that atmospheric oxygen levels were negligible until the Great Oxidation Event (GOE) at 2.4–2.1 Ga. The burial of organic matter is balanced by release oxygen, and if rate exceeds efficient sinks, can accumulate limited oxidative weathering. relative to total carbon be inferred from isotope record in sedimentary carbonates matter, which provides a proxy for source flux through time. Because there are no large secular trends over time, it commonly...
The body fossil and biomarker records hint at an increase in biotic complexity between the two Cryogenian Snowball Earth episodes (ca. 661 million to ≤650 years ago). Oxygen nutrient availability can promote complexity, but (particularly phosphorus) redox dynamics across this interval remain poorly understood. Here, we present high-resolution paleoredox phosphorus phase association data from multiple globally distributed drill core through non-glacial interval. These are first correlated...
The Toarcian Oceanic Anoxic Event (T-OAE; ~183 Mya) was a globally significant carbon-cycle perturbation linked to widespread deposition of organic-rich sediments, massive volcanic CO 2 release, marine faunal extinction, sea-level rise, crisis in carbonate production related ocean acidification, and elevated seawater temperatures. Despite recognition the T-OAE as potential analog for future deoxygenation, current knowledge on severity global anoxia is limited largely studies trace element...
Abstract Northwest Africa 13134 is a coarse‐grained gabbro with an oxygen isotopic composition consistent Martian origin and classified as enriched shergottite based on its bulk trace element abundances La/Yb ratio of 1.53. The meteorite composed framework large pyroxene rods up to 6 mm in longest dimension (64% by area) interstitial maskelynite (formerly plagioclase; 28% area). Minor phases include merrillite apatite, Fe‐Ti oxides, Fe‐sulfides; such baddeleyite, tranquillityite, fayalitic...
Abstract Earth's carbon cycle maintains a stable climate and biosphere on geological timescales. Feedbacks regulate the size of surface reservoir, million‐year timescales must be in steady state. A major question about early Earth is whether was cycled through reservoir more quickly or slowly than it today. The answer to this holds important implications for state, time, expression atmospheric biosignatures Earth‐like planets. Here, we examine total inputs outputs from over time. We find...
Abstract Modern anoxic marine sediments release phosphorus (P) to seawater, driving feedbacks at multiple timescales. On sub‐Myr timescales, P regeneration amplifies ocean deoxygenation; on multi‐Myr it stabilizes atmospheric O 2 . Some authors have extended this thinking the Precambrian: by analogy, widespread anoxia would imply extensive from sediments. However, neglects role of sulfate in regeneration. While abundant seawater today, was scarce Precambrian. Here a simple model is used...
Abstract Molecular nitrogen (N 2 ) constitutes the majority of Earth's modern atmosphere, contributing ~0.79 bar partial pressure ( p N ). However, fluctuations in may have occurred on 10 7 –10 9 year timescales past, perhaps altering isotopic composition atmospheric nitrogen. Here, we explore an archive that record deep time: foliage cycads. Cycads are ancient gymnosperms host symbiotic ‐fixing cyanobacteria modified root structures known as coralloid roots. All extant species cycads to...