About

I am an earth scientist (B.S. in geology and Ph.D. in geochemistry) with primary interests in the early Earth, the origin of life, and the evolution of the continental crust. I investigate these processes using the geochronology and composition of accessory minerals (for example: zircon, shown at left). The first half billion years of Earth history lack a confirmed rock record, but bore witness to many of the important events that shaped our planet's subsequent evolution. The formation of the Moon, likely magma ocean(s), and potentially the origin of terrestrial life occurred in this epoch, and each played crucial roles in forming the blue planet we know today. My research has focused on using the geochemistry and included minerals in detrital zircon to investigate the composition of ancient crust that has since been lost to erosion and recycling. Better rules for matching inclusion petrology and host zircon geochemistry to origins in specific types of magma or tectonic settings will a

Research topics

• Geology
• Paleontology
• Astrobiology
• Physics
• Geochemistry
• Biology

Selected publications

• Searching for Concordancy between the U-Pb and Ar-Ar Radiometric Systems in Various Types of Apollo Impactites

  Abstracts with programs - Geological Society of America · 2025-01-01

  articleSenior author
  PublisherDOI

• What the zircon record reveals about the habitability of the Hadean Earth

  Elsevier eBooks · 2025-12-05

  book-chapterSenior author
  PublisherDOI

• Medically Integrated Dispensing Pharmacy: ASCO-NCODA (Network for Collaborative Oncology Development & Advancement) Standards Update

  JCO Oncology Practice · 2025-05-27

  article

  ASCO Standards are evidence-based standards to provide frameworks for best practices in cancer care, following the standards development process as outlined in the ASCO Standards Policies and Procedures Manual . ASCO Standards follow the ASCO Conflict of Interest Policy for Clinical Practice Guidelines . Standards and other guidance (“Guidance”) provided by ASCO is not a comprehensive or definitive guide to treatment options. It is intended for voluntary use by clinicians and should be used in conjunction with independent professional judgment. Guidance may not be applicable to all patients, interventions, diseases, or stages of diseases. Guidance is based on review and analysis of relevant literature, and is not intended as a statement of the standard of care. ASCO does not endorse third-party drugs, devices, services, or therapies and assumes no responsibility for any harm arising from or related to the use of this information. See complete disclaimer in Appendix 1 (online only) for more. PURPOSE To update standards for dispensing oral anticancer medications and supportive care medications using a medically integrated dispensing pharmacy (MIP). METHODS A multidisciplinary expert panel of oncology professionals integral to MIP and a patient representative participated in updating the guidelines. The revised standards address patient-centered and operational interventions of MIP that improve the access, quality, safety, and outcomes of prescribed oral anticancer medications or other supportive care medications. A systematic literature review was conducted to identify primary studies of interventions designed to improve MIP that were published between May 2019 and August 2024. RESULTS Using studies that met the intervention criteria and studies that were useful in determining gaps that need to be addressed by MIP standards, the standards were revised, restructured, and expanded into two primary domains: patient-centered quality standards and operational quality standards. Domain 1 centers on health equity and social determinants of health, drug access, patient safety, education, and adherence to maximize treatment outcomes. Domain 2 focuses on logistics and care coordination and waste prevention. CONCLUSION These revised and expanded ASCO-Network for Collaborative Oncology Development & Advancement standards further enhance existing guidance to practices and outpatient clinics engaging in or planning to initiate MIP. The goal is to improve clinical outcomes and patient satisfaction through adherence to rigorous standards in oral anticancer medication management, patient safety, and care coordination. Additional information is available at www.asco.org/standards .

  PublisherDOI

• Preserved carbon isotope compositions in 3.7 billion year old detrital organic matter from the Isua Supracrustal Belt

  Communications Earth & Environment · 2025-03-28 · 3 citations

  articleOpen access

  Abstract Graphite found along contiguous horizons in the metamorphosed detrital sediments from the ≥ 3.7 Ga Isua Supracrustal Belt in Southwest Greenland may represent the oldest remains of life on Earth. Here, we examine the carbon isotope compositions of graphite occurring in situ as inclusions in minerals in both metasediment and secondary vein lithologies by secondary ion mass spectrometry. The carbon isotope composition of the metasediment-associated graphite displays a significantly narrower spread in δ 13 C values (average –20.6 ± 1.8‰, 1 standard deviation) than vein-associated graphite does (–20.4 ± 3.8‰), which can be explained by different origins, respectively interpreted as detrital biogenic matter and abiotic fluid-precipitated graphite. Additionally, graphite within metasedimentary porphyroblasts displays lower δ 13 C values (–20.9 ± 1.6‰, down to –26.4 ± 0.5‰) than graphite in the surrounding matrix (–18.1 ± 1.7‰), indicating the former to be less altered than the latter.

  PublisherOA PDFDOI

• Root Problem of Mid‐Tertiary Cordilleran Detachment Faults

  Geophysical monograph · 2025-04-11

  other

  The North American Cordilleran metamorphic core complex belt provides insight into the tectonometamorphic evolution of North America. Garnet-bearing assemblages have been used to generate pressure-temperature (P-T) constraints on the metamorphic history in its northern and central segments. Such datasets are scarce in its southern segment. We review existing metamorphic conditions and timing for these core complexes. Conditions from the Whipple detachment shear zone in southeastern California were also ascertained using conventional and isopleth thermobarometry. A sample from the easternmost Whipple Mountains shows monazite in reaction with allanite trapped in garnet. The monazite was dated in situ using an ion microprobe and yield 62±9 Ma, 67±7 Ma, and 80±6 Ma (Th-Pb dates, ±1s). P-T conditions recorded by garnet and matrix minerals from an adjacent rock are high-grade (rim, 680-750°C and 7-9.4 kbar and core, 750-800°C and 6.2-7.8 kbar). The results suggest exhumation from depths deeper than previously thought. With this new information, a new pressure-temperature-time path may be established for the rocks in the Whipple detachment and may suggest a deeper initiation or multiple metamorphic events not previously analyzed.

  PublisherDOI

• Beyond Pristinity: Rethinking Lunar Samples and Their Role in Planetary Evolution

  Abstracts with programs - Geological Society of America · 2025-01-01

  article
  PublisherDOI

• Origin and age of low-temperature carbonates in oceanic hotspot lavas

  Geochimica et Cosmochimica Acta · 2025-11-01 · 1 citations

  articleSenior author
  PublisherDOI

• Inter-method differences (SIMS vs. IRMS) in oxygen isotope fractionation: insights from Chinook salmon otoliths

  Geochimica et Cosmochimica Acta · 2025-11-02

  articleOpen access

  Stable oxygen isotopes (δ 18 O) in biogenic carbonates serve as a valuable proxy for reconstructing thermal history. Fish otoliths (ear stones) are particularly useful, as they precipitate continuously throughout life, creating a temporally resolved archive of water temperature. Here, we calibrate the temperature-dependent oxygen isotope fractionation equation for Chinook salmon ( Oncorhynchus tshawytscha ) using two analytical methods, secondary ion mass spectrometry (SIMS) and isotope ratio mass spectrometry (IRMS), to assess method-specific effects on fractionation equations and their implications for otolith-based thermometry. Juvenile fish were reared for 15 weeks under controlled freshwater conditions (salinity < 0.1 ppt) with a stable ambient water δ 18 O of − 5.54 ‰ (VSMOW) (±0.10, 1 SD) at three temperatures (11, 16, 20 °C). Otolith δ 18 O values measured by SIMS showed a significant linear inverse relationship with ambient water temperature: 1000 l n α = 11.51 ± 1.39 , 1 S E × 10 3 T ( K ) - 1 - 10.94 ± 4.80 , 1 S E δ 18 O otolith ( V P D B ) - δ 18 O w a t e r V S M O W = - 0.14 ± 0.02 , 1 S E × T ( ° C ) + 0.64 ( ± 0.27 , 1 S E ) . Applying this equation yielded water temperature reconstructions with an accuracy of ± 1.97 °C and a precision of ± 0.70 °C (1 SD). A paired comparison revealed SIMS δ 18 O values were on average 1.97 ‰ lower than IRMS values, likely due to matrix effects and organic content. This offset produced large differences in equation intercepts, leading to reconstructed temperatures from IRMS-based equations that deviated ∼ 10 °C from observed temperatures when applied to SIMS data. In contrast, the slopes (thermal sensitivity) of SIMS and IRMS equations were highly consistent, indicating that relative temperature changes can still be reliably inferred from SIMS δ 18 O values using IRMS-based equations. Greater variability in SIMS δ 18 O values compared to IRMS may partly reflect fine-scale isotopic heterogeneity within otoliths, suggesting that SIMS-based temperature reconstructions may require larger sample sizes or additional calibration tailored to specific contexts. Across-species comparison of fractionation equations revealed that inter-method differences exceeded inter-species differences, highlighting the need for method-matched equations for accurate absolute temperature reconstructions. Despite these challenges, once calibrated, SIMS-based otolith thermometry provides a powerful tool for reconstructing fine-scale fish thermal histories and assessing habitat refugia and resilience to climate change.

  PublisherDOI

• Pervasive impact modification of pristine lunar clasts

  Nature Communications · 2025-03-13 · 2 citations

  articleOpen access

  Lunar rock fragments, particularly those deemed pristine, have long been considered vital records of the Moon’s formation and magmatic evolution. These fragments were thought to have largely escaped the Moon’s intense impact history, offering a window into the early lunar crust. However, the concept of “pristine” is increasingly debated, as traditional criteria for identifying pristine samples—based on texture, mineral content, and siderophile element abundances—may overlook the extensive effects of impact reworking. In this study, we apply a novel high-resolution geochemical and experimental approach, linking zircon Al content to parent melt composition, to critically assess lunar samples. Our findings reveal that clast zircons, assumed to preserve magmatic history, and matrix zircons, considered the last igneous remnants in brecciated samples, are not in chemical equilibrium with their surrounding glass. This disequilibrium, coupled with heterogeneous zircon ages, provides compelling evidence for pervasive impact reworking, challenging the assumption that these samples represent primary igneous lithologies. These results underscore the need for a serious re-evaluation of lunar materials. New analytical tools, tailored to each critical lunar lithology, will be essential for this reassessment—such as the Al-in-zircon method employed here for zircon-bearing samples. This study challenges the long-standing assumption that some lunar samples are pristine, revealing pervasive impact modification. Using Al-in-zircon geochemistry, we demonstrate that key lunar rock fragments are not primary magmatic products, raising fundamental questions about the accuracy of lunar evolution models and the very records used to reconstruct the Moon’s history.

  PublisherOA PDFDOI

• Uptake of ammonium and nitrate by calcium carbonate polymorphs

  2025-01-01

  article

  The abundance of nitrogen ionic species in natural waters is linked to drivers of environmental change at the global and local scales throughout the anthropogenic era. The potential for calcium carbonate minerals as a resistant host material to record the reactive nitrogen composition of natural waters is driving a requirement to understand incorporation mechanisms and to develop absolute analytical techniques that operate at the µm scale. To assess the capability of calcium carbonate for the uptake of dissolved nitrogen compounds, we conducted an experimental study on the incorporation of ammonium and nitrate into inorganic carbonate crystals. Calcium carbonate polymorphs were synthesized in nitrogen-containing growth media and were used to quantify nitrate and ammonium uptake by calcite, aragonite, and vaterite phases. Automated colourimetry analyses yielded partition coefficients between mineral and fluid ranging from (D(NO3)) of 2.12·10-2 to 6.51·10-1 regardless of CaCO3 polymorph (i.e. calcite and aragonite). Secondary ionisation mass spectrometry (SIMS) demonstrated ammonium is more readily incorporated into polymorphs of vaterite and aragonite (D(NH4) = 8.77·10-3 and D(NH4) = 1.63·10-2, respectively), as opposed to calcite (D(NH4) = 3.09·10-3). SIMS was also used to assess the degree of nitrogen heterogeneity within crystal phases. Calcite rhomboids were found to have high internal heterogeneity, with an almost two orders of magnitude shift in N concentration due to inferred sectoral zoning. The polycrystalline nature of aragonite spherulites mitigated intra-spherulite heterogeneity, resulting in analytical repeatability of <10% standard deviation (1 s.d.) when N(CaCO3) = 164–169 ppm. Inter-spherulite variability for aragonite polymorphs was calculated to average 7.6% (1 s.d.), thus demonstrating a potential for development of reference materials for high precision analytical techniques. Despite the heterogeneity observed across the various synthesized CaCO3 polymorphs, the technique appears to have potential for use as a SIMS calibration dataset and for estimating absolute nitrogen concentrations in the carbonate palaeorecord at the µm scale.

  PublisherDOI

Frequent coauthors

• T. Mark Harrison

  University of California, Los Angeles

  85 shared

• P. Boehnke

  38 shared

• Heather M. Kirkpatrick

  29 shared

• Dustin Trail

  23 shared

• M. M. Wielicki

  Geological Survey of Alabama

  20 shared

• C. Brenhin Keller

  Dartmouth College

  18 shared

• Ellen Alexander

  University of Colorado Boulder

  14 shared

• S. J. Mojzsis

  14 shared

Education

• Ph.D., Earth and Space Sciences

  UCLA

  2013

• B.S., Geological Sciences

  University of South Carolina

  2008