The sixth extinction belongs to us

The Sixth Extinction: An Unnatural History, Elizabeth Kolbert, Henry Holt and Company, hardcover, 319 pages with index, with charts and illustrations, $28.

Extinction occurs so slowly we rarely know it's happening. A pigeon here, a woodpecker (maybe) there, a near-miss with a condor. We are, however, 200,000 years into an extinction event that likely will change everything we know about life on earth. Recognized or not, it is a mass extinction, the sixth extinction, and it belongs to us.

"The Sixth Extinction," a book by Elizabeth Kolbert, briefly explains the five previous mass extinctions on earth and their causes. The sixth extinction, examined in detail, not so coincidentally began at the time humans began to migrate out of Africa, Kolbert says. This extinction is moving at a pace far exceeding geologic time scale. She calls it the Anthropocene extinction. Anthro comes from the Greek word for humans.

Kolbert is an excellent writer, clear with facts, and with a sense of humor, not that this is a humorous topic. The stories she offers as examples of what is happening to us are well chosen and crisply written. The topic is important to us even though the ending will not be known for hundreds of thousands of years. It looks to be tough going between now and then.

The five pervious mass extinctions each ended a geological era, from the Ordovician, 444 million years ago to the Cretaceous, "only" 60 million years behind us. The latter is attributed to a huge astroid that slammed into the Yucatan Peninsula, ending dinosaurs and about 75 percent of all life on the planet.

The collision produced what Kolbert calls "a vast cloud of searing vapor and debris that raced over the continent, expanding as it moved, and incinerating everything in its path." How hot? How fast? Kolbert quotes a geologist's explanation: "Basically, if you were a triceratops in Alberta you had about two minutes before you were vaporized."

Not all extinction events have such profound and immediate affect. They usually are measured in geologic time. The one we're living through will be so, but has a local pace that can be breathtaking.

Kolbert tells her story by visiting 13 of those local places. She tells the story of how a particular creature disappeared forever.

For example, amphibians. They are the world's most endangered class of animals, Kolbert says. The background rate of extinction, that which happens in the course of time, is probably about one amphibian species in a thousand years, according to educated estimates. A more exact number is not available because frogs and their relatives are not built to leave fossil remains.

No one is going to actually witness that once-in-a-thousand-years extinction. Today, however, "Pretty much every herpetologist working out in the field has observed several extinctions," she writes.

Kolbert says that in the course of writing this book, she encountered one frog species that has since gone extinct, and three or four others now extinct in the wild. It is not just herps. Every living thing is under this pressure to some degree. Things that we have yet to name are going extinct.

You know what's happening. It's land use and chemicals and weather change. It's us. It can be as simple as cutting a road through a forest.

Kolbert writes of an on-going habitat experiment named the Biological Dynamics of Forest Fragmentation Project. Among its findings are the behaviors of two South American bird species. White-crowned Manakins cross roads at will. The Scale-backed Antbird, however, is very reluctant to do so. A new road, then, can reduce the readily used territory for that bird. With enough roads that bird eventually can be reduced to nowhere to live and nothing to eat.

We're cutting the world into ever-smaller pieces, among the long list of other things we're doing. You might wonder if any bird species nesting in Minnesota reacts to highways, roads, and driveways in this fashion. If so, we most likely will know when it's too late to do much about it.

Can we stop what we are doing to our planet? Can we even slow the Anthropocene extinction? It doesn't seem so today, does it? We will, however, get to watch it happen. We have front-row seats at the disaster movie in which we star.