Species die-offs are common. For most of Earth’s history, the rate of speciation (the creation of new species) has outpaced the rate of extinction (the dying out of existing species). This has led to the tremendous biodiversity we see today. During certain periods, however, the extinction rate has outpaced the speciation rate, leading to a decline in Earth’s biodiversity. These periods, when they go on long enough and bring about the demise of many species, are called mass extinctions.

“Postcards from the 6th Mass Extinction” Explore Encyclopædia Britannica's endangered species audio series. Encyclopædia Britannica, Inc./Patrick Riley

“Losing the Vaquita in the Northern Gulf of California: What Would It Mean?” John Rafferty of Encyclopædia Britannica discusses the challenges of protecting the world's smallest porpoise, the vaquita, from extinction. This is the first part of the Postcards from the 6th Mass Extinction audio series. Encyclopædia Britannica, Inc.

“The Incredible Shrinking World of the Polar Bear” John Rafferty of Encyclopædia Britannica discusses the polar bear, a mammal that is among the world's largest carnivores on land, and the threats to its survival. This is the second part of the Postcards from the 6th Mass Extinction audio series. Encyclopaedia Britannica, Inc.

“Bluefin Tunas and the Problem of Overfishing” John Rafferty of Encyclopædia Britannica discusses the Atlantic and Pacific bluefin, two species of tunas that are threatened by overfishing. This is the third part of the Postcards from the 6th Mass Extinction audio series. Encyclopædia Britannica, Inc.

“The Precarious State of the Monarch Butterfly” John Rafferty of Encyclopædia Britannica discusses two species of monarch butterflies in North America that have declined as a result of habitat loss and the effects of pollution. This is the fourth part of the Postcards from the 6th Mass Extinction audio series. Encyclopædia Britannica, Inc.

“The Orangutan Conservation Conundrum” John Rafferty of Encyclopædia Britannica discusses the challenges that oil palm cultivation poses to orangutans. This is the fifth part of the Postcards from the 6th Mass Extinction audio series. Encyclopædia Britannica, Inc.

“Understanding Functional Extinction” John Rafferty of Encyclopædia Britannica and Dr. Andrew Solow of the Woods Hole Oceanographic Institution discuss the concept of functional extinction. This is the sixth part of the Postcards from the 6th Mass Extinction audio series. Encyclopaedia Britannica, Inc.

“The Demise of the Northern White Rhinoceros” John Rafferty of Encyclopædia Britannica and Dr. Barbara Durrant of San Diego Zoo Global discuss the precarious status of the northern white rhinoceros (Ceratotherium simum cottoni) and some of the medical techniques that could be used in its recovery. This is the seventh part of the Postcards from the 6th Mass Extinction audio series. Encyclopædia Britannica, Inc.

“Amphibian Apocalypse” John Rafferty of Encyclopædia Britannica and Dr. Karen Lips of the University of Maryland discuss the chytrid fungus called Batrachochytrium dendrobatidis (Bd) and how it has decimated amphibians worldwide. This is the eighth part of the Postcards from the 6th Mass Extinction audio series. Encyclopaedia Britannica, Inc.

“Coronavirus Origins and Conservation” John Rafferty of Encyclopædia Britannica and Dr. Jonna Mazet of the University of California, Davis, discuss the origins of the coronavirus SARS-CoV-2 and the processes by which emergent viruses spill over from one species to another. This is the ninth part of the Postcards from the 6th Mass Extinction audio series. Encyclopædia Britannica, Inc.

So far there have been five notable mass extinctions. A growing number of ecologists, climatologists, and other scientists argue that Earth is now in the midst of its sixth. The purpose of the audio series Postcards from the 6th Mass Extinction is to document this extinction as it happens—and, more importantly, to identify solutions that may slow its pace.

Mass extinctions are caused by several factors, including chemical changes to Earth’s atmosphere and oceans, changes in the arrangements of the continents, and cataclysms (such as long-lasting volcanic events and collisions with asteroids and comets). Much evidence today indicates that this sixth mass extinction is being caused by the activities of only one species, Homo sapiens (that is, modern human beings). The current rate of human-induced extinctions is estimated to be between 100 and 1,000 times greater than past natural (background) rates. This situation is largely due to the exponential growth in the number of humans on Earth and their activities. Population has increased from about 1.3 billion people in 1850 to more than 7.8 billion in 2020. Human activities that most threaten other species include pollution, overhunting and overfishing, and transforming forests and other natural ecosystems into agricultural and other human-dominated ecosystems.

Extinction on such a massive scale can be a difficult concept to get one’s head around. Its seriousness as it relates to the future of life on Earth is profound. Postcards from the 6th Mass Extinction attempts to personalize extinction, emphasizing the survival challenges that familiar, often cherished forms of life currently face, while at the same time considering the pivotal roles they play in their own ecosystems. This audio series also identifies the solutions we humans might apply to improve their odds of survival. This is tough stuff—understandably—but Postcards from the 6th Mass Extinction aims to provide the context needed to understand the significance of the problem unfolding before our eyes. Knowing more can empower us to make different decisions regarding our own appetites for natural resources and to work for social and environmental change.