*Ancient Microbial Communities is part of Sumner's research which includes understanding microbial evolution and ecology and Earth history through  microbial signatures in the rock record. Her publications feature new developments in how to interpret ancient biological responses to environmental factors, tracing oxygenation and the impact on carbonate microbial biological signatures. Sumner has also studied carbon isotopes of specific carbonates in order to find evidence of life.
*Antarctic Lakes Sumner's research utilizes Antarctic lakes as a model system for understanding microbial processes, early oxygenic photosynthesis, and life on other planets. This work includes the discovery of pinnacles of microbial growth under ice-covered lakes and describes multiple microbial communities involved in the development of these features.  Similar features in another Antarctic lake appear to record changes in the lake environment, including sea level, through time.
*Exploration of Mars and its Environments Professor Sumners research with the Mars Science Laboratory has generated over three dozen collaborative publications and helped uncover evidence of ancient lakes on Mars. Sumners research has established that parts of ancient Mars could have hosted life as we know it on Earth, and contributed to the discovery of organic molecules on Mars. As a geologist, Sumner applies many of the same principles that would be used on earth, such as stratigraphy and geochemistry, to the Martian environment. Sumner is a MSL “long term planner”, one of several lead geoscientists amongst more than five hundred scientists not directly employed by NASA on this project. Sumner was involved in the creation of a geological map of Gale crater, and selecting the landing site of Curiosity. Sumner was partially responsible for the assignment of daily operations to fit the long-term missions goals. and also involved in future planning for additional Mars exploration, including a mission in 2020.
*Neoarchean Geological Time Period is a part of Professor Sumners research that has been accumulated in South Africa. Sumner has studied the precipitation of multiple elements including carbonate and aragonite. This research has led Sumner to develop new understandings of the oceans pH in Neoarchean time period which can lead to discoveries in the changes of the oceans pH through time. Sumners conducted this research using methods of stratigraphy and petrography.