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Faculty

David Johnston

Dr. David Johnston

Professor of Earth and Planetary Sciences
& Co-Director of Graduate Studies
He/Him/His
Primary research interests: Isotope geochemistry and historical geobiology; re-animating ancient ecosystems and ocean chemistry using stable isotope systems, chemical speciation techniques, modern microbial experiments (for calibration) and theoretical considerations.

CV

Staff

Associated Researchers

Graduate Students

Val Aguilar

Val Aguilar

1st Year Ph.D Student
She/Her/Hers

Val received her BS in Earth Sciences (paleobiology & geology) from UC Santa Barbara in 2021. As an RA at Johns Hopkins University, she became interested in using lab and field techniques to answer questions related to perturbations in Precambrian biogeochemical cycles. At Harvard, Val works in the Drabon & Johnston lab groups, where she hopes to use isotope geochemistry and sedimentology as tools to characterize disturbances on early Earth. Her research currently involves unravelling how the Archean biosphere and surface environment changed as a result of large extraterrestrial impacts.

Ana Gonzalez Valdes

Ana Gonzalez Valdes

5th Year Ph.D Student

Ana Gonzalez Valdes received her B.A. in Earth Sciences from Columbia University in 2016. At Columbia and Caltech she worked to understand how microbes in unique environments cycle nutrients like phosphorus and sulfur. At Harvard Ana will be spanning the Johnston and Pearson labs and hopes to dig deeper into microbial nutrient cycling and how it can be measured isotopically.

Daianne

Daianne Höfig

1st Year Ph.D Student
She/Her/Hers
My name is Daianne, and I am originally from Brazil, where I obtained a BSc in Geology and an MSc in Geochemistry. During my studies at Texas A&M University, I transitioned from U-Pb zircon geochronology to organic geochemistry. Isotopes are my favorite tools to (1) research how biogeochemical cycles operated in past climate systems and (2) anchor these key climate events to precise timeframes. As a member of the Johnston lab, I aim to become proficient in using stable isotope geochemistry to address geobiological questions across different time scales and numerical modeling.

Ella

Ella Hughes

3rd Year Ph.D. Student
Ella is coming to Harvard from the UK, where she completed a BA degree in Natural Sciences and MSc degree in Earth Science at the University of Cambridge. Her Master’s research at Cambridge and Caltech focussed on the sulfur isotope composition of organic matter, and as part of the Johnston lab she is hoping to expand her knowledge of stable isotope geochemistry as a tool to approach biogeochemical questions.
K Keller

Katherine Keller

4th Year Ph.D Student
She/Her/Hers
Katherine received her BA in Environmental Chemistry from Columbia University in 2014. Since then, she has worked at the US Geological Survey on Quaternary paleoceanogprahic and hydroclimate reconstruction in the Arctic. At Harvard, she will be working in the Johnston and Schrag labs.
Haley

Haley Olson

3rd Year Ph.D. Student
She/Her/Hers
Haley received a BA in Geology from Carleton College in 2017. Haley's research uses stable isotope geochemistry to constrain marine geochemical conditions throughout geologic time (thus far from the Archean to the Neogene). She is currently focused on the Paleozoic and understanding how the sulfur cycle responded to the proliferation of land plants and how sediments record large volcanic events.

Gone, but not forgotten

Erin Beirne

Erin Beirne

Former Johnston Lab Manager
Now a Research Associate in marine environmental chemistry at Bigelow Laboratory for Ocean Sciences
Emma_photo

Emma Bertran

Former gardute student

The intimate interaction between microbial life and earth leaves specific chemical signatures that record information on microbial activity, and paleo-environmental conditions. As a geobiologist, my goal is to interpret these signatures and reconstruct an accurate picture of paleo-environments and microbial communities, and the nature of their co-evolution through time. To date, I have focused on the sedimentary biogeochemical sulfur cycle and its main metabolic pathways: microbial sulfate reduction and microbial sulfur disproportionation. These run the reductive and oxidative branches of the sedimentary sulfur biogeochemical cycle, respectively. As such, they respond to and track the evolution of Earth’s surface redox conditions. Deconstructing the net preserved isotopic signature into its individual metabolic components requires a thorough understanding of the biochemistry of each, and of the environmental information enclosed in their specific sulfur isotopic signatures. For this, I apply a wide range of research tools. These include stable isotope geochemistry, environmental observations, pure culture microbial experiments (using both wild-type and deletion mutant strains), modeling of intracellular dynamics, and construction of three-dimensional models of crucial proteins in these key metabolic pathways.

For more details on current projects and a list of publications, please visit my website!

Alex Bradley

Alex Bradley

Former Postdoctoral Fellow

Now on the faculty at Washington University at St Louis.

Alyssa Chan

Alyssa Chan

Former Undergraduate Thesis Student

Alyssa is a senior concentrating in Chemistry and Earth and Planetary Sciences, with a secondary field in the Comparative Study of Religion. She joined the Johnston group in Summer 2014. Her thesis research involves evaluation of organic molecules as potential proxies for atmospheric oxygen isotopes.

Chloe-Rose

Chloe-Rose Colombero

Former Undergraduate Research Assistant
Chloé-Rose is a senior at Harvard College concentrating in Organismic and Evolutionary Biology with a secondary field in Earth and Planetary Sciences, focusing on marine sciences. She joined the Johnston group in the summer of 2020 to work on a phylogenetic project tracing the metabolic consequences of oxygen reactive microbe species across marine and hot spring environments.
Ben Cowie

Ben Cowie

Former Post-doctoral Fellow

Ben is an isotope geochemist with diverse interests in the Earth sciences. In the Johnston Group, he is currently exploring questions surrounding the evolution of the atmosphere and biosphere over the most recent billion years of Earth history using a triple-oxygen isotope approach.

He received his Ph.D. from the University of Calgary in 2013 for developing a novel stable isotope approach for characterizing oil sands reservoir fluids, and was awarded a Vanier Canada Graduate Scholarship for his work. From 2002 to 2008 he attended McMaster University in Hamilton, Canada where he earned B.Sc. and M.Sc. degrees in Earth and Environmental Sciences. His research during this time focused on compound-specific isotope analysis of lipid biomarkers with application to environmental remediation and monitoring. From 2006 to 2010 Ben was part of the Pavilion Lake Research Project team, a NASA Exploration Analog site, and an international collaborative research project. The project provides insight into the earliest life on Earth, and aims to change the way humans explore outer space.

Viv

Vivien Cumming

Former Research Associate, Harvard University

Viv is a photographer, filmmaker and writer specialising in documenting Earth science stories and expeditions. After postdocs at McGill and Harvard, Viv...

Read more about Vivien Cumming
Renata Cummins

Renata Cummins

Former Undergraduate Thesis Student

Switched coasts and is working in the Bay Area, CA

Ben Gill

Ben Gill

Former Post-doctoral Fellow

Now on the faculty at Virginia Tech.

Maddie Goldberg

Maddie Goldberg

Undergraduate Research Assistant
I’m a junior studying Earth and Planetary Sciences with a secondary in Educational Studies. I joined the Johnston group in the spring of 2019 as an undergraduate research assistant and am now beginning my senior thesis with the lab, conducting isotope analysis on sulfur-bearing hydrothermal vent minerals.
Frasier Liljestrand

Frasier Liljestrand

Former Graduate Student

Frasier got his BS in Earth Science from Rice University in 2013. While he was at Rice, he did research in biogeochemistry focusing broadly on trying to quantify global carbon fluxes and budgets. Here in the Johnston group Frasier hopes to expand his knowledge of global sulfur cycling and how the global cycles are expressed locally.

M_Miller

Matthew Miller

Former Undergraduate Research Assistant
My work mainly focuses on establishing novel mineral proxies to track sulfur cycle dynamics in deep time, notably carbonate-associated sulfate (CAS). This system, alongside the robust yet infrequent barite record, potentially represents a powerful way to track sulfur and oxygen isotope behavior in order to constrain marine chemistry in the past. Additionally, I have started some culture work with the sulfate-reducing bacterium Desulfovibrio vulgaris, and am currently investigating the evolution of its isotope-fractionating metabolism.
Alex Morgan

Alex Morgan

Former Thesis Student

Alex is now at Cambridge University working on her master's degree.

Tor O'brien

Former Thesis Students

Now a PhD candidate at Washington Univesrity in St. Louis working with Dave Fike