Graduate Students

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 Höfig

1st Year Ph.D Student
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 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
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 Olson

3rd Year Ph.D. Student
Haley received a BA in Geology from Carleton College in 2017. After graduating, she worked as a TA for a geology field camp in New Zealand and as a lab assistant in the Johnston lab. Haley is interested in merging her interests in field geology, sedimentology, and stable isotope geochemistry. She currently uses sulfate-bearing rocks and the triple oxygen isotope system to examine past climates and marine chemistry.