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94 5 Vanishing Life Gumwood (Commidendrum; top), St. Helena plover (Charadrius sanctaehelenae; left), and Trochetiopsis (right), endangered species of St. Helena Island. Vanishing Life 95 the human species is a recent development in Earth’s history. Our lineage, the hominin lineage, comprising extinct human relatives and extant humans, arose between 5 million and 8 million years ago. Compared with creatures like the platypus and the spiny anteater , the last of the egg-laying mammals, whose lineages diverged between 20 million and 50 million years ago, and the first vascular plants, which appeared an estimated 410 million years ago, our species has existed but a moment in Earth’s history. So although we may consider ourselves to be an extraordinarily intelligent species , we are among the planet’s youngest, and consequently, our cumulative amount of experience with nature is relatively small. At times throughout our history this inexperience has revealed itself in uneasy fashion, in our mindlessly killing wild animals and tearing plants out of the ground, in our letting self-interests control the fate of our environment, in our throwing tantrums because we are not permitted to drive our off-road vehicles across tender wildernesses. Many do not realize that we are in the midst of a mass extinction episode, the sixth such event in Earth’s history. Mass extinction is defined by the loss of multiple groups of organisms, particularly genera and families, within a brief span of geologic time. Such events are a part of Earth’s natural history, and much of what is understood about extinction in the modern era has come from studies of the fossil record. This meticulous, though incomplete, account of the history of life on Earth tells us what happened during the five earlier mass extinctions, which included the Ordovician extinction, the Late Devonian extinction, the End Permian extinction, the End Triassic extinction, and the ensuing End Cretaceous (or CretaceousTertiary ) extinction, which did away with many species about 65 million years ago. All the while, persisting between and among these five major events, there was a continuous level of “background” extinction, characterized by the periodic loss of comparatively few species here and there. But whereas the five previous mass extinctions have been attributed to factors such as climate change, movement of Earth’s tectonic plates, sea-level fluctuations, volcanic activity, and the occasional freak asteroid, the current, sixth mass extinction period appears to be due to human activities and their contributions to climate change. Naturally occurring changes in climate have been implicated but 96 out of nature appear to be insignificant, especially relative to the human-induced onset of global warming, which has drastically altered natural processes , to the point that they will be forever linked to our existence. The human impact on biodiversity first expressed itself a few millennia back in Earth’s time. Between 10,000 and 50,000 years ago, our ancient ancestors appear to have played a central role in the disappearance of large mammals. The woolly mammoth disappeared about 3,700 years ago, coincident with a period of climatic warming, which reduced the animal’s habitat. The mammoth, however, had managed to survive such warming periods prior to the appearance of human hunters. With the emergence of the first organized human civilizations, human activities became focused on manipulating the immediate environment. Rather than only hunt large mammals or gather plants, humans learned to bring certain species under their control, eventually producing populations of domesticated livestock and crops. Domesticated species required space, and as villages grew into cities, more land and shelter were needed. As civilizations have grown and expanded throughout history, the continuity of Earth’s environment has become increasingly disrupted. Animals that could once travel across wide expanses of forests and grasslands are now confined to fragmented habitats surrounded by walls of humanity, their populations stunted and their survival threatened. Up until the latter half of the twentieth century, most knowledge of human-induced extinction focused on the loss of individual species . Among the extinct creatures whose stories have been repeatedly told are the dodo, which disappeared from Mauritius in the late seventeenth century, having been hunted to its end, and the passenger pigeon, the last wild one having been shot in 1900 and the last captive bird having died in 1914. Over the last several centuries, many other species have disappeared from Earth, far more than could have been lost by natural law alone. According to the International Union for Conservation of Nature and Natural Resources...

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