The Last Extinction: Megabeasts’ Sudden Death written and produced by Doug Hamilton (review)

The history of life on Earth is punctuated by “mass extinction events:” spasms of upheaval when dozens, hundreds, or even thousands of species were obliterated in, geologically speaking, the blink of an eye. The most famous, 65 million years ago, ended the age of the dinosaurs and set the stage for the evolutionary flowering of mammals. The most severe, 225 million years ago, killed off between 90 and 95 percent of the species then in existence: a biological catastrophe so severe that paleontologist Michael Benton titled his popular account of it When Life Nearly Died. The most recent took place at the end of the last Ice Age—between 60,000 and 10,000 years ago—and killed off a significant fraction of the world’s large mammals. It wiped out 7 of the 23 genera (groups of closely related species) of large mammals in Europe, 15 of 16 in Australia, 46 of 58 in South America, and 33 of 45 in North America. The result was the biological world in which humans made the transition from nomadic hunting to village agriculture and, thousands of years later, to urban civilization.

The Last Extinction—an hour-long episode of the PBS-TV science documentary series Nova—focuses on the North American side of the Ice Age extinction and, specifically, on the 15 genera (encompassing 20-25 species) that vanished from the fossil record a little less than 13,000 years ago. The species lost in that final pulse of extinction include some of the most spectacular ever seen on the continent. Mastodons, mammoths, and lions bigger than their African cousins were among the lessremarkable victims, which included saber-toothed big cats, giant beavers that grew to eight feet long and well over 200 pounds, and giant ground sloths with the height of a giraffe and the girth of an elephant. Strangest of all, perhaps, was the glyptodont: an enormous herbivore with an armored shell, like an armadillo grown to the size of a Volkswagen Beetle. Why they died out—when similarly sized species like the elk, moose, bighorn sheep, American bison, and grizzly bear survived—remains a puzzle.

The narrative core of The Last Extinctionis a story about scientists’ investigation of one piece of that puzzle: the possibility that a comet impact may have caused, or contributed to, the extinction. Traditional explanations—long-term climate change, or over-hunting by the prehistoric “Clovis people” who appeared in western North America around 13,000 years ago—receive only brief attention. This is a film about scientists looking for, and finding, evidence that a comet (or, possibly, several comets) struck the Earth around the time of the extinction, filling the skies with debris and producing a sharp, sudden drop in global temperatures.

Novahas always excelled in the presenting scientific detective stories, and The Last Extinctionis no exception. It ranges across both field and lab, following geologists into the deserts of Arizona, paleoclimatologists onto the glaciers of Greenland, and an extraterrestrial-impact expert into a NASA research facility where he simulates comet strikes with glass pellets. The camera looks over the scientists’ shoulders as they gather their data, and it participates, as an unacknowledged observer, in artfully staged discussions of the data’s significance. Scientists are rarely depicted justexplaining something, or silently contemplating evidence. They are nearly always shown in action, and the camera attends carefully to the details of whatthey are doing: the way they hold and use their tools, label their sample containers, and gesture at data on computer screens to make a point. It conveys a sense of science as an activity, and a way of engaging with the world.

The two best scenes in The Last Extinctionreveal the intensity of that engagement. The first shows paleontologist James Hansen rendered speechless—overcome with emotion—at a major breakthrough in a problem that has fascinated him literally since boyhood. The sight of his...