Kolbert argues that Homo sapiens has accomplished what no other species has: permanently and irreversibly altering Earth's atmosphere and biosphere.

Kolbert travels to Panama after reading an article suggesting dying golden frogs may be evidence of an ongoing Sixth Extinction.

Scientists identify a chytrid fungus as the culprit behind frog deaths, killing amphibians by blocking electrolyte absorption through their skin.

Cuvier delivers a public lecture in Paris arguing that mastodon bones belong to a wholly lost, extinct species.

The last surviving pair of great auks is killed by collectors seeking rare specimens on Eldey Island, Iceland.

Walter Alvarez discovers an unusually iridium-rich clay layer between limestone bands in a gorge in Gubbio, Italy.

The Alvarezes publish a paper arguing that a six-mile asteroid wiped out three-quarters of all species at the end of the Cretaceous period.

Scientists determine that the first of the Big Five extinctions, which killed 85 percent of marine species, was caused by rapid glaciation.

Kolbert visits Castello Aragonese island to observe how natural CO2 vents are causing ocean acidification and devastating nearby marine life.

Studies reveal that the Great Barrier Reef's coral cover has declined by 50 percent within just the past three decades.

Miles Silman's tree plot studies reveal that global warming is driving Peruvian tree genera upslope at a rate of eight feet per year.

Bird population surveys in Amazon forest fragments show a continual decline long after initial displacement, resulting in local extinctions.

Wildlife biologists conducting a bat census in an Albany cave find nearly all bats dead, covered in a mysterious white powder.

Kolbert argues that large animals disappearing precisely when early humans arrived in their regions supports the overkill hypothesis.

An exhibit at the American Museum of Natural History declares that humanity is currently causing the Sixth Extinction.

Elizabeth Kolbert's investigation begins with the alarming disappearance of Panama's golden frogs, her first on-the-ground evidence that a Sixth Extinction may already be underway. She traces the scientific history of extinction theory from Cuvier's mastodon studies to the human-caused obliteration of the great auk, building a foundation for understanding how species vanish. The Alvarezes' discovery of an iridium-rich clay layer in Gubbio provides crucial context for how sudden, catastrophic extinctions occur, linking past events to the present crisis. Kolbert then visits sites around the world — Castello Aragonese, the Great Barrier Reef, the Peruvian tropics, and Albany's bat caves — to document extinctions being driven by ocean acidification, climate change, and invasive species. Her encounters with collapsing bat populations and the evidence behind the overkill hypothesis connect ancient extinctions directly to patterns of modern human behavior. The book closes with a museum exhibit that confirms what Kolbert's global journeys have demonstrated: humanity is the primary force behind a catastrophic Sixth Extinction.

The headline events of humanity's role in the Sixth Extinction.

The golden frog of Panama, once so common it appeared on lottery tickets and taxicabs, begins vanishing mysteriously from western Panama.

Scientists at the El Valle Amphibian Conservation Center capture surviving golden frogs and house them in secure, disinfected glass tanks.

European-American troops discover enormous bones — tusks, teeth, and a giant femur — in a smelly Ohio River marsh, sparking scientific debate.

Charles Lyell publishes Principles of Geology, and a young Charles Darwin reads the first volume at the start of his sea voyage.

Alfred Newton determines the great auk is extinct and campaigns for a hunting ban, leading to the first wildlife protection law.

Paleontologist Neil Landman discovers that ammonites were thriving right up until the Cretaceous asteroid impact, overturning earlier assumptions.

Danish chemist Paul Crutzen coins the term 'Anthropocene' to describe the current geological epoch dominated and reshaped by human activity.

Marine biologists find that no calcifier species near the Castello Aragonese vents has adapted to the altered pH despite centuries of exposure.

Chris Langdon's repeated experiments in multiple environments confirm that lower ocean pH saturation states halt coral reef growth.

A scientific study projects that between 22 and 31 percent of species will be committed to extinction due to ongoing habitat loss.

Tom Lovejoy reveals that large-scale Amazon deforestation would not only eliminate species but also eliminate the region's rainfall entirely.

Scientists determine that the deadly white-nose bat fungus was most likely introduced to the Albany area through a commercial tourist cave.

Early captive Sumatran rhino breeding programs nearly doomed the species after keepers fed the animals hay instead of required fresh foliage.

Kolbert visits La Ferrassie in France to examine one of the largest caches of Neanderthal bones ever discovered.

San Diego Zoo researchers rush to preserve cells from the body of the last po'ouli bird, hoping to enable future recovery efforts.

From the golden frog's disappearance in western Panama to the preserved cells of the last po'ouli bird, Pool 2 follows the secondary but essential stories that build Kolbert's case for a Sixth Extinction. Early chapters trace the scientific origin of extinction theory, from the discovery of mastodon bones along the Ohio River to Lyell's landmark geology text and Newton's first wildlife protection campaign. Middle chapters document discoveries that connect past extinction events to the present, including Landman's ammonite studies and Crutzen's coining of the term Anthropocene. Kolbert moves through marine, forest, and cave environments to show how ocean acidification, deforestation, and invasive species are dismantling ecosystems at an accelerating pace. The failed early captive breeding programs for the Sumatran rhino and Kolbert's visit to the Neanderthal bone site at La Ferrassie add further depth to the book's argument that human activity reshapes and eliminates life. The final preservation of po'ouli cells at the San Diego Zoo captures the bittersweet reality of humanity's belated efforts to undo its own damage.

The supporting discoveries and species stories behind the Sixth Extinction.

Kolbert accompanies Edgardo Griffith on a field expedition and realizes the rescued frogs will never return to the rainforest floor.

Cuvier's landmark public lecture introduces the revolutionary concept that species can permanently vanish from Earth, forever changing scientific thinking.

Darwin's theory of natural selection provides the first scientific framework explaining both the emergence of new species and the extinction of existing ones.

Darwin's discovery that the great auk went extinct during his own lifetime disproves his belief that extinction was too slow to be observable.

Scientists realize that Lyell had been reading the fossil record backward — what appeared as gradual species decline was actually a record of sudden catastrophic extinction.

Kolbert learns that only tiny creatures survived the Cretaceous asteroid impact, a post-catastrophe shrinkage of surviving life called the Lilliput effect.

Thomas Kuhn's concept of the paradigm shift explains scientists' long resistance to accepting catastrophic extinction theories.

Hall-Spencer warns that the entire marine ecosystem will begin to crash when ocean pH levels drop to 7.8.

Selina Ward warns that without immediate cuts to carbon emissions, coral reefs will be reduced to scattered remnant patches.

Kolbert learns that global warming is advancing ten times faster than the post-ice-age warming, leaving species little time to adapt.

The concept of extinction debt emerges to describe the gap between species already committed to extinction and those that have actually disappeared.

Scientists conclude that human transportation has recreated a New Pangaea by mixing previously isolated species from across the globe.

Terri Roth achieves the first successful Sumatran rhino birth in captivity at the Cincinnati Zoo after years of failed breeding attempts.

Paabo's genome research concludes that as modern humans spread across the globe, they drove Neanderthals and other archaic human species to extinction.

Kolbert reflects that humanity's power to decide which species survive and which disappear will be humanity's most enduring legacy.

Pool 3 follows the key moments of discovery and intellectual realization that form the spine of Kolbert's argument for a Sixth Extinction. From the moment Griffith's rescued frogs are recognized as permanently exiled from the wild, to Cuvier's revolutionary idea that species can vanish forever, each event marks a fundamental shift in understanding. Darwin's theory of natural selection and its uncomfortable implications — including his own witnessing of human-caused extinction — set the stage for a new scientific paradigm that forced naturalists to categorize a new kind of loss. The Alvarezes' decoding of the fossil record, the identification of the Lilliput effect, and Kuhn's paradigm shift concept together explain how scientists slowly and reluctantly accepted catastrophic extinction theories. Moving into the present, Kolbert documents revelations about coral reef collapse thresholds, extinction debt, and the New Pangaea, each one tightening the link between human activity and mass extinction. The book's emotional weight accumulates through moments like Roth's first successful rhino birth and Paabo's Neanderthal genome findings, culminating in Kolbert's sobering reflection on humanity's role as Earth's most powerful life-altering force.