Approximately 66 million years ago, an asteroid struck the Earth, triggering a chain of events that would end the reign of the dinosaurs and usher in the age of mammals. Despite its colossal scale, this incident was not the only event of its kind—in fact, it wasn’t even the first. Rather, it’s only the most recent mass extinction our planet has witnessed across its 4-billion-year lifespan. In the last 500 million years alone, the Earth has experienced five major extinction events, each of which dramatically altered the planet and left a trail of fascinating geological evidence for us to uncover.

In the six lectures of Earth’s Great Extinctions, geologist Rachel Phillips digs deep into these mass extinction events, known as the “Big Five,” utilizing the fossil record to explore what caused them, how life recovered after each one, and what they can teach us about modern climate change and extinctions. From the ice age of the Ordovician period to the “Great Dying” of the Permian extinction to the climate catastrophe that ended the dinosaurs, you’ll explore the many factors that led to these events and what they can tell us about Earth in both the past and the present.

There is a growing scientific consensus that we are in the early stages of a sixth mass extinction. While the changes the planet is undergoing are human-driven, the ultimate causes—global temperature change, sea-level change, desertification, and other impacts—are not so different from the mass extinctions of the past. Better understanding how and why these catastrophic events occurred is not just an exercise in exploring the past, but a crucial step in determining our own future.