To look into the eyes of a frog is to travel back in time. The earliest amphibians hoisted themselves out of the water some 370 millions years ago, long before there were any birds in flight, mammals scurrying around or even dinosaurs stomping the Earth. A full chronicle of amphibian history would start prior to the existence of the seven continents, when the only land mass on our planet was a sprawling expanse scientists have labelled Pangaea, not yet splintered by tectonic plates.
Squishy and soft though they may be, amphibians are in fact hardy survivors. Since life appeared on Earth 3.5-billion years ago, there have been five major extinction events, traumatic changes in climate and environment that have felled many, and sometimes most, species existing at a particular moment. With their mournful, limpid eyes, amphibians have witnessed four of these five extinction events, the most spectacular and notorious being the asteroid that wiped out the dinosaurs and many other species 65 million years ago.
The unsettling news of Elizabeth Kolbert's powerful book The Sixth Extinction is that we are witnessing a wide-scale dying off of species comparable to the earlier extinction events. An early and startling symptom of the sixth extinction is the sudden and global collapse of countless varieties of frogs, the very animal whose ancestors were so adept at surviving. The culprit behind this extinction is no asteroid but a single species: humanity. In countless ways, we are rendering the Earth uninhabitable to many of our fellow Earth-dwellers.
Summing up the scientific consensus, Kolbert notes that "it is estimated that one-third of all reef-building corals, a third of all freshwater molluscs, a third of sharks and rays, a quarter of all mammals, a fifth of all reptiles, and a sixth of all birds are headed toward oblivion."
Why is our planet once again turning into a spherical graveyard? Climate change is a major cause. It's darkly ironic that the very dinosaurs wiped out by that fateful asteroid are now the fossil fuels igniting another extinction event. But beyond climate change, the full impact of which we only have a small glimmer of, many of the traits that make humanity so successful as a species are also lethal to other lifeforms. Our versatility and cleverness have allowed us to expand into virtually every corner of the globe, bringing into fragile ecosystems invasive new species that eliminate all the local competition.
Humanity has so thoroughly transformed the planet that we may be the first life form that deserves to have a geological epoch named after us, the Anthropocene (the term is gaining popularity in scientific circles although hasn't been formally accepted yet by the International Commission on Stratigraphy). Before the Anthropocene is over, much of what we now call zoology will become a branch of paleontology. Those animals that survive won't live in the wild but will be domesticated or be confined to prisons we call reserves and zoos. In order to insure the reproduction of the survivors, the most intimate relations of these animals will be carefully monitored by the species that brought them to the abyss of non-existence.
Mass extinction is a grim topic, yet Kolbert's book is an exhilarating read. A staff writer for The New Yorker, Kolbert has wisely marshalled her arguments into the form of an intellectual adventure. She notes in passing that one of the scientists she meets "decided to become a paleontologist when he was seven, after reading a Tintin adventure about a dig." Perhaps taking a cue, Kolbert has cast herself as Tintin, a globe-trotting reporter joining field researchers all over the world as they try to solve the ultimate murder mystery: Why are so many animals dying and how can we stop it?