David Johnston, Harvard University Lisa Levin, Scripps Institute of Oceanography
The Cambrian radiation, during which essentially all major animal body plans appeared in the fossil record ~540 million years ago, is one of the most important evolutionary events in Earth history. In recent years, hypothesized triggers for this event have focused on a rise in predation and increased levels of oxygen in the world's oceans. We propose to test the linkage between these hypotheses. We postulate that the high oxygen demand of carnivory (animals feeding on animals) is the key linkage. The hypothesis outlines that carnivory (animals eating other animals) was limited by low levels of atmospheric oxygen. As the late Precambrian Earth transitioned to a more oxygenated state, this lifestyle (carnivory) and ultimately the Cambrian explosion ensued. Here, we will test both the biological and geological predictions of this hypothesis. The biological prediction, that oxygen limits carnivory in animals, will be tested by constructing and analyzing a database of published marine bottom dwelling animal surveys, coding how each animal feeds, and examining how oxygen levels and other environmental parameters affect feeding behavior. The geological prediction, that oxygen increased near the Precambrian-Cambrian boundary, will primarily be tested by generating sedimentary geochemical data (focusing on iron, carbon and sulfur) from the spectacular Neoproterozoic stratigraphic record of northwestern Canada in the Ogilvie, Wernecke and Mackenzie Mountains. Together, these two tests of this integrative causal hypothesis for the Cambrian radiation will provide new insight into this important geobiological event. This grant provides funding to train two levels of researchers. First, the grant provides funding for a post-doctoral scholar who will work between the Principal Investigators at Scripps and Harvard to accomplish the goals of the proposal. The post-doctoral scholar will also will work with the Center for Ocean Sciences Education Excellence to deliver a filmed public lecture in the Perspectives on Ocean Sciences series at the Birch Aquarium. These are widely distributed talks (broadcast to 15 million homes; ~200,000 web views per year) and will be instrumental in disseminating the results of the modern global ocean compilation to the public and demonstrating how ancient oceans can inform responses to modern oceanographic change. Second, two undergraduate students, one from Harvard and one from an undergraduate-oriented institution, will gain both field experience in northwest Canada and lab experience in sedimentary geochemistry through this grant.