Monday, April 20, 2015

The Sixth Extinction: The Snake in the Garden is -- Us



            The Sixth Extinction: This one is on us.           
            Almost everything we're likely to know about human life, society, history, our own lives and times is simply useless, irrelevant, when we consider the history of the planet Earth. That's the underlying premise of "The Sixth Extinction" by New Yorker journalist Elizabeth Kolbert.
            We're still just a blip on the radar screen of the geological history of the planet. But when we disappear from that history, we will have left a mark on the geological record (visible to who or whatever comes after) that tells of a period of widespread species extinctions. The massive die-off of life forms, already apparent across the globe, and across all the branches of the tree of life, has a single, traceable cause: the human species.
            The fossil record goes back roughly 600 million years. Taking the long view, one authority quoted in "The Sixth Extinction," concluded that most species "are at a low risk of extinction most of the time" except for "rare intervals [of] vastly higher risk." Thus the history of life on planet Earth can be described as "long periods of boredom interrupted occasionally by panic." 
            Right how, human beings are putting an end to the boredom.
            The officially recognized extinctions came at the end of the Ordovician Period (marine life only, 60 percent of invertebrates disappear) 450 million years ago; in the late Devonian, 370 million years ago (most extant fish die; cause unknown); the end of the Permian, 252 million years (the worst extinction, taking 96 percent of marine species plus a mass extinction of insects and vertebrates from a runaway Greenhouse Gas effect); the late Triassic (most  dinosaurs disappearing, possibly from climate change and massive volcanoes), 201 million years; and the end of the Cretaceous (three-quarters of plant and animal species gone from an asteroid impact), 66 million years ago.
            So now, as "The Sixth Extinction" reports from the author's visits to numerous ongoing biological projects and the studies they generate, we can add to such calamities as asteroid collision, heavy atmosphere-darkening volcanic activity, wobbles in the earth's orbit caused by the moons of Saturn, continental drift, and the rise of the Himalayas, the widespread domination of Earth by a single species, homo sapiens. The Earth welcomes plain old us to the ranks of the major extinction causes.
            Our role in rapidly increasing species loss goes back to the swift spread (by geological time reckoning) of our ancestors from Africa to Asia, Europe, and all the other continents.We arrive and the woolly mammoth, the giant sloth, sabre-toothed tigers and many other mega-fauna dwindle and ultimately disappear. A process that may take a few thousand years is a snap of the fingers in the fossil record. Human beings, Kolbert's authorities hypothesize, may not have intended to wipe them out, but survival mechanisms that worked well in the past -- growing too large for attack by predators -- proved helpless against our weaponry.
            Other mammals and birds, like the wolves of North America, were simply in our way once we had moved into their habitat. The buffalo were consciously exterminated by a conquering, imperial breed of humans (now called 'Americans'). Other species lost their hold on existence because we saw them simply as a resource: the fate of the passenger pigeon, treated as a cheap protein source.
            Large animal species that disappear around the same time that human beings spread into their territory include other branches of the hominid family from which we emerged. Most of us are at least vaguely familiar with the Neanderthals, the first Europeans. We took over the caves, shorelines and hunting grounds where they lived and left a record, making tools from flint in the same way for tens of thousands of years. Besides the Neanderthals, a branch of smaller cousins tagged "Hobbits" disappear from the fossil record shortly after our arrival. Lately remains providing evidence of still another hominid species called Denisovans have been discovered. Where are they now? "Hobbits," Denisovans -- We hardly knew ye!
            Smaller species fall victim to the unintended consequences of our dominance. We cut down trees, we turn grasslands to farmlands: local plants, insects, higher animals and invertebrates disappear. We burn hunks of the rain forests to make room for more people. But simply breaking up a tropical habitat by a road or a utility line directly correlates with a sharp loss in biodiversity, according to Kolbert's on-the-ground sources. Species that made it in large areas can't survive in small, chopped-up ones.
            Our farming and animal raising, mining and factories, change environments. Pollutants, chemical run-off, agricultural pesticides, suburban lawn fertilizers all destroy biota. Expanding populations hunt third-world forests for body parts of elephants, gorillas, tigers sold for profit.
            Other species simply diminish and go extinct in consequence of our unique mobility, moving ourselves and our goods from region to region, continent to continent. The minor pest from one continent, hitching a ride on trade good, becomes a killer plague in the land across the ocean.
            "What life's history reveals, in its ups and downs," Kolbert writes, "is that life is extremely resilient but not infinitely so."
            The implications for the survival of the species that is causing the disappearance of so many others remain to be seen.