When a 10 km-wide meteorite slammed into the Earth roughly 65 million years ago, megatsunamis sloshed across the oceans and a front of superheated particles swept across the surface, outward from the impact site located in modern-day Mexico. Most significantly, a thick cloud of dust enshrouded much of the planet for years, leading to wild temperature swings and presenting crippling challenges to plants accustomed to clear skies.

By the time the iridium-rich dust had settled, as many as 75% of the planet’s species (the dinosaurs most famous among them) were spiraling toward extinction, never to be seen again. It was clearly a bad day for the biosphere – a stark, sudden event that was unequivocal in its destructive trajectory. The advent of human civilization may not seem as menacing as a fiery ball of death, but given our proclivity for global transportation systems, extraction and oxidation of hydrocarbons, and co-option of vast tracts of land, we may well be having an equally disastrous effect on the natural world.

This is the contention of The Sixth Extinction, the most recent environmental tour de force from New Yorker staff writer Elizabeth Kolbert. (Geologists and paleontologists have identified five “major” extinction events over the 4.5 billion year history of our planet, making the current convulsion the sixth.)

Quantifying humanity’s effect on the biosphere is an enormous tabulation challenge, with several moving targets. New species – and even entirely new biomes – continue to be discovered, even as our understanding of what species are and what diversity means constantly shifts. Nonetheless, it’s impossible to deny that things are changing. Many beloved species are on the ropes, while others, the “invasive species” humans have enabled, thrive.

Kolbert gives this epidemic of extinctions a face – fungus-covered as it may be – in her well-reported collection of case studies. “In my reporting, I kept bumping up against he fact that climate change was just a part of a larger global story of change,” Kolbert says. Viewing that change through a biological lens, she generated an account that’s part travelogue, part field journal; Kolbert’s presence and dry wit throughout the proceedings ground the narrative in a clear-eyed (read: depressing) account of ecological disaster. “You are taken along with me in these expeditions,” she explains, “so I hope that gives the book a sense that you’re discovering things as I’m discovering them. I wanted to give a sense of continuity through different time scales and different places.”

Along the way, as we hop from a Panamanian frog hotel to a Scottish waterfalls to Icelandic bays, Kolbert comes to the conclusion that it’s not so much the magnitude of the environmental changes our species is causing – though by the time it’s all said and done, we might set records in that category too – but rather the rate at which we’re causing them. In order to remain within climatic regimes for which their finely tuned biology is evolved, many organisms would need to emigrate, and quickly. Scientists have even determined the speed of the treadmill: in the Peruvian rainforest, plants would need to move roughly 30 feet per day just to keep pace. Ignoring the evacuation warning – staying put and adapting – isn’t in the cards for most organisms, as their rates of evolutionary change are several orders of magnitude slower than the changes taking place around them.

Kolbert ends with the fateful proclamation that “we are deciding, without quite meaning to, which evolutionary pathways will remain open and which will forever be closed. No other creature has ever managed this, and it will, unfortunately, be our most enduring legacy.” But even that may be giving our intervention too much credit: the brush isn’t nearly so fine as to “decide” much of anything. This is wholesale destruction, plain and simple.

The only thing missing from the exhaustive account from the front lines is a sense of how we might slow the insidious progress of extinctions across the planet. But to Kolbert, a simple prescription would have cheapened the issue, improperly simplifying an enormously complicated problem. “I decided pretty early on,” she recalls, “given the complexity of the subject, that I wasn’t going to wave my hands at the end and say, this is how we’re going to solve this.”

“But I think that people are interested in knowing things even if they’re very dark. This is just a story that ought to be told.”