The Sixth Extinction: An Unnatural History

Elizabeth Kolbert, 2014

Executive Summary

There have been five mass extinction events in the history of life on Earth — moments when a significant fraction of all species were wiped out in a geologically brief period. Elizabeth Kolbert’s argument, built from years of reporting alongside scientists in the field, is that we are living through the sixth. Unlike the previous five, this one has a cause that can be identified: us. The Sixth Extinction is not a polemic. It is journalism at its best — rigorous, specific, and quietly devastating. The thesis: the scale of human impact on the biosphere is now comparable to the asteroid that ended the Cretaceous, and we are the only extinction-causing force in Earth’s history that could, in principle, choose differently.

5 Core Arguments

  1. Extinction is not normal background noise — Species go extinct continuously at a low baseline rate. What is happening now is orders of magnitude above that baseline — current extinction rates are estimated at 100 to 1,000 times the pre-human norm. This is not natural attrition. It is a pulse, and pulses of this magnitude have a cause.
  2. The mechanisms are multiple — Kolbert profiles distinct drivers of extinction through the lens of specific species: habitat destruction, ocean acidification, the spread of invasive species via global trade, direct hunting, and climate change. No single mechanism tells the whole story; the combination is what makes the current crisis unprecedented.
  3. Ocean acidification as canary — One of the book’s most important contributions is its treatment of ocean chemistry. As atmospheric CO₂ rises, the oceans absorb more carbon dioxide, becoming more acidic. This threatens the calcium carbonate structures — shells, coral skeletons — that underpin marine food webs. The chemistry is not controversial; the consequences are unfolding in real time.
  4. The Great American Interchange as precedent — Kolbert uses the prehistoric meeting of North and South American fauna — when the land bridge formed and species mixed — as a case study in what happens when previously isolated ecosystems collide. The results were catastrophic for many South American species. Global trade is now engineering similar collisions at a scale and speed that evolution cannot match.
  5. We are the asteroid — The book’s organizing metaphor: the asteroid that struck Yucatán 66 million years ago was not malicious, but it was transformative. Human activity — through no single decision or actor — is now a geological force. The difference is that asteroids cannot reflect on what they are doing.

Kolbert and Carson

The line from Carson to Kolbert is direct. Carson documented what industrial chemistry was doing to a single class of organisms in a specific country over a few decades. Kolbert documents what industrial civilization is doing to the entire biosphere over centuries. Both are making the same civic argument: that the consequences of human decisions are being externalized onto the natural world, and that accountability requires knowing what those consequences are. Both were attacked for making that argument. Both were right.

A Respectful Disagreement

The Sixth Extinction is an excellent work of science journalism, and like most science journalism it occasionally oversimplifies. The extinction rate estimates Kolbert relies on are genuine scientific consensus, but they carry real uncertainty — measuring extinction is methodologically difficult, and some critics argue the figures overstate the crisis. Kolbert does not engage deeply with this uncertainty, which gives the book a more settled authority than the underlying science always supports.

The book is also stronger on diagnosis than prescription. Kolbert does not pretend to have solutions, which is honest — but readers who finish the book looking for a path forward will not find one here. That is not a flaw, exactly, but it is a limitation worth naming.

Bottom Line

The Sixth Extinction won the Pulitzer Prize for a reason. Kolbert is a gifted reporter who makes complex science accessible without distorting it, and who brings genuine moral seriousness to a subject that could easily become either sensationalism or despair. She achieves neither. What she achieves is clarity — the kind that makes it harder to look away.

Read it alongside Leopold. Leopold gives you the ethical framework; Kolbert gives you the current ledger.

“Though it might be nice to imagine there once was a time when man lived in harmony with nature, it’s not clear that he ever really did.” — Elizabeth Kolbert

PRH | huffmanwrites.org | © Philip Huffman