By Shari Ellis
Bonnie Jacobs is a renowned paleobotanist in the Roy M. Huffington Department of Earth Sciences at Southern Methodist University. She studies fossil plants—from microscopic cells to macroscopic leaves, fruits, seeds and wood. Bonnie has conducted field work in Texas and New Mexico as well as Kenya, Tanzania and Ethiopia.
Bonnie is perhaps best known for her work with leaf fossils to interpret past climate change. The size and shape of leaves along with information about the environment where modern relatives of the plant live are used to estimate average annual rainfall and temperature. When plants are very well preserved, even the leaf surface can provide clues to the past.
A type of leaf structure that is especially informative is the stoma (plural: stomata), an opening in the leaf surface through which carbon dioxide goes in and oxygen and water vapor go out. Scientists have found a relationship between carbon dioxide concentration in an environment and the relative frequency of stomata for some species of plants. As Bonnie explains, “If you look at dried pressed plants—say a red oak—from 1910, 1920, 1930, and on to 2010, you will see that the frequency of stomata on the leaf surface decreases as carbon dioxide in the environment increases. So, if you have a fossil red oak leaf, you can plot the relationship and estimate the paleo carbon dioxide concentration.” In that way, fossil plants help us understand past climate, which is essential for testing the accuracy of computer models of the potential impact of present-day climate change on the Earth’s ecosystems.
Bonnie’s path to the world of macrofossils seems to combine a little bit of inevitability with luck or happenstance. As a child growing up in New York City, she loved ancient things. “I loved the American Museum of Natural History and the Metropolitan Museum of Art. I would breeze through the art and head straight to the mummies and Egyptian artifacts.” At SUNY Buffalo she continued to nurture her broad interests in nature and ancient cultures, creating her own degree in geology and anthropology with an emphasis on archaeology. Bonnie’s pursuit of interdisciplinary research led her to the University of Arizona for graduate school. She initially planned to do geological work in relation to an archaeological context, but took a course in palynology—the study of pollen—and grew interested in older and older time periods. And frequent field work opportunities in Mexico offered by the University of Arizona sparked an interest in the Neotropics.
Bonnie collected 42,000-year-old fossil pollen from the southwestern U.S. for her dissertation; however, much of the analysis actually took place in Kenya because her husband, Louis Jacobs, had taken a job at the National Museum of Kenya. Today, Bonnie acknowledges she was very worried about her move to Africa. “While I had my samples, I had no idea whether there would be any microscopes. Also, I had no colleagues or friends to talk about my work, no library and, of course, no internet. I was very worried. The museum was very poorly equipped, but I was able to use amazing lab facilities run by a retired Harvard professor that was funded by the World Bank and used primarily by foreign researchers studying animal diseases.”
Upon completing her degree, Bonnie was awarded funds to study African macrofossils. She observes, “Kenya offered tremendous potential for studying human evolution and environments, but there was not much work documenting the environment of human evolution in relation to plants. The pre-Pleistocene record was completely blank so the opportunity just presented itself!” Until recently the only American to study African macrofossils, Bonnie’s excitement is still palpable: “The time period during the transition from Oligocene to Miocene is very exciting. Talk about real ecosystem change! 24 million years ago, Africa was connected to Eurasia and there was a big turnover in faunas. It was at the time that the classic Africa fauna was established. So the question is, how did grasslands evolve?”
When asked about the role of amateurs in the field, Bonnie acknowledged they play many important roles. “One of the roles that first comes to mind is the critical eyes on the ground. Another role is outreach. They reach large numbers of people of all ages and turn people onto science!” Bonnie stressed the role clubs play in educating the public, “Clubs are critical for getting the word out to folks about what science is and why science is important! And not just about cool dinosaurs, but about paleoclimate and modern day climate and extinction, the processes of science and preponderance of evidence.”
You can read more about Bonnie’s research in Africa in her contributions to the New York Times “Scientist at Work” blog.
Bonnie is part of the GroundWork Dallas project that includes scientific research and educational outreach.
You can read one of Bonnie’s research papers on the evolution of the African grasslands here.