Tanja Bosak was awarded the 2011 James B. Macelwane Medal and a Conferred Union Fellows at the AGU Fall Meeting Honors Ceremony, held on 7 December 2011 in San Francisco, Calif. The medal is for “significant contributions to the geophysical sciences by an outstanding young scientist.”

Tanja Bosak was awarded the 2011 James B. Macelwane Medal at the AGU Fall Meeting Honors Ceremony, held on 7 December 2011 in San Francisco, Calif. The medal is for “significant contributions to the geophysical sciences by an outstanding young scientist.”  

Tanja Bosak was born and raised in the small Croatian village of Kumrovec, also the birthplace of the Yugoslav dictator Tito. At the age of 13, Tanja won admission to Croatia’s best high school, MIOC, in Zagreb. To attend MIOC, which specialized in mathematics and computer science, Tanja moved to Zagreb and lived in a state boarding house for teenage girls. Tanja later attended Zagreb University. She intended to major in physics but soon shifted to geophysics. Setting her sights on a Ph.D. in planetary science, Tanja applied to the California Institute of Technology (Caltech) and was accepted. Her first paper, written with Andrew Ingersoll, is on Kelvin-­Helmholtz instabilities in Jupiter’s atmosphere.

Atmospheric physics soon became the road not taken. A second research project at Caltech brought Tanja into contact with Kenneth Nealson and Lisa Stein, who introduced her to the wonders of microbiology. Dianne Newman then arrived at Caltech, and Tanja became her first student. Dianne pointed Tanja toward an ideal problem for a geophysicist seeking to reconstruct herself as a geobiologist: the origin of stromatolites. Stromatolites are laminated sedimentary structures that are thought to be Earth’s earliest fossils. Various lines of evidence, most notably, their unusual geometry, suggest that stromatolites record the presence of ancient microbial life, but precisely how has remained a fundamental question. Tanja’s unique contributions to this subject have derived from her desire to explain field observations with insight gained from carefully controlled laboratory experiments and quantitative theoretical models. One thus sees an expression of her early training in physics and mathematics.

In Dianne Newman’s lab at Caltech, Tanja detailed the ways in which microscopic calcite precipitates are influenced by microbes. After postdoctoral work with Ann Pearson and Richard Losick at Harvard, Tanja continued her work on stromatolites as an assistant professor at the Massachusetts Institute of Technology (MIT). Tanja and MIT graduate student Alex Petroff noted that small conical stromatolites tend to be spaced about 1 centimeter apart. They then showed, by a combination of theory and experiment, that the centimeter spacing represents a diffusive length scale associated with a diurnal cycle. These results support the hypothesis that conical stromatolites record the presence of early photosynthetic cyanobacteria.

Conical stromatolites often display bubble-­like features of uncertain origin. By growing stromatolites in the lab, Tanja and her students have been able to show that microbial growth around oxygen-­rich bubbles results in the preservation of these features. Since oxygen is a by-­product of photosynthesis, the onset of preserved bubbles may record the origin of oxygenic photosynthesis.

Stromatolites are but one of Tanja’s interests. A hint of her future can be seen in her recent collaboration with her MIT colleague Shuhei Ono. Sulfate-­reducing microbes grown in Tanja’s lab turn out to fractionate sulfur isotopes much more so than previously thought. This simple observation may require a substantial revision of the Proterozoic history of atmospheric oxygen.

For these and other accomplishments, those yet to come, and her uniquely physical approach to geobiology, I am delighted to recognize Tanja Bosak as a 2011 James B. Macelwane medalist.



—Daniel H. Rothman, Massachusetts Institute of Technology, Cambridge

Thank you, Dan, and thank you, AGU, for this honor. Like Dan said, my scientific path so far has had its fair share of lucky turns, so I would like to thank many people who have helped me along the way. The fortuitous nature of it all really hit me when I tried to trace my scientific roots back to something. Growing up in a small—and I mean small—village in Croatia, I attended the local public school, where math, science, and language classes offered much-needed balance to patriotic songs and stories about President Tito. In high school I thought I might like to be a biologist, but all the ones I knew were working either abroad or as librarians. So I ended up studying physics and geophysics. I thank my parents, Marica and Ivan, for all their support during this time and for not insisting that I become an accountant. Following a vague notion that I could study other worlds, I went to the Jet Propulsion Laboratory (JPL) for a summer of undergraduate research and then applied to graduate schools in planetary science. Once at the California Institute of Technology (Caltech), I learned about another stunning and bizarre planet: the early Earth. I was lucky that Dianne Newman, my mentor, colleague, and friend, suggested that I work on stromatolites, a project that united biology, chemistry, physics, and the early Earth. Without Dianne’s support, optimism, generosity, and contagious delight in science, I would not be standing here today. Special thanks also go to Joe Kirschvink, the wild child of geobiology. During my postdoc at Harvard, Rich Losick helped me explore the world of genetics, Ann Pearson guided me in organic geochemistry, and Andy Knoll and Paul Hoffman shared their stories from Earth history. At the Massachusetts Institute of Technology (MIT) I have truly enjoyed working with my new colleagues Dan Rothman, Shuhei Ono, and Roger Summons and with my collaborators Sara Pruss, Francis Macdonald, Dan Lahr, and Hojatollah Vali. Also, luckily, I have had great graduate students, Alexander Petroff and Min Sub Sim, as well as motivated research assistants and undergraduates. Finally, all this would be much less fun without my fellow explorer of bizarre worlds Ben Weiss. Thank you! —Tanja Bosak, Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge