Though turbidity currents are massive and frequent underwater events, we have rarely observed them directly. Esther Sumner is one of the few researchers who has. In the podcast, she describes what it's like to instrument an active submarine canyon, what these flows have revealed about the way sediment moves across the seafloor — and the day her team accidentally flew an underwater robot into a live turbidity current in the Mendocino canyon off the coast of California. She is an Associate Professor of geology and geophysics at the University of Southampton.

A key question about the early history of the Solar System is whether the giant planets formed roughly at the distances from the Sun they presently occupy, or, as some theories predict, much closer to the Sun. The discovery of other solar systems with radically different configurations of planets has made this question more pressing, since it appears that the configuration of the Solar System might be atypical.

In the podcast, Hal Levison explains why the Trojan asteroids of Jupiter offer us the best opportunity to discriminate between the various models of Solar System evolution. And that is why a spacecraft called Lucy is now well on its way to a rendezvous with these asteroids.

Hal Levison is the Principal Investigator of the Lucy mission. He studies the dynamics of astronomical objects and, in particular, the formation and long-term behavior of solar system bodies. He is one of the original proponents of the Nice model (named after the city where it was conceived), a scenario that proposes the migration of the giant planets from an initial compact configuration closer to the Sun to their present positions. He is Chief Scientist in the Department of Space Sciences at the Southwest Research Institute in Boulder, Colorado.

The first multicellular animals to build reefs lived in the Early Cambrian around the time of the Cambrian explosion. They were sponges called archaeocyaths. In the podcast, Sara Pruss suggests that the rise of the archaeocyaths fostered an increase in animal diversity. But they were relatively short-lived, and when they died out in the Middle Cambrian, the diversity declined. Over geological time, reef-building organisms appear and disappear again and again until the corals we have today appeared in the Middle Triassic, about 240 million years ago.

Pruss is currently trying to understand why reefs are such a persistent feature of the geological record, despite the environmental stresses imposed on them. She is a Professor of Geosciences at Smith College.