40. The Anthropocene
Summary While humankind already had exerted noticeable influences on the Earth and life since the Cognitive and the Agricultural Revolutions, these influences dramatically increased since the Industrial Revolution. In the beginning of the 21st century virtually all cultivatable land is cultivated, most large land animals live in human captivity while many others are on the verge of extinction, vast quantities of resources are extracted from the Earth’s lithosphere, forests become megacities, and greenhouse gases accumulate in the Earth’s atmosphere and lead to a global warming. While the increase of human power is impressive, it also demands humans to use it wisely and in a responsible way, for its own sake and the sake of all other living species.
Keywords Earth’s Atmosphere; Global Warming; Mass Extinction; Population Growth; Shortage of Resources
Open-pit mining of gold in Australia in 2010. Human mining activities especially since the Industrial Revolution had a major impact on the Earth’s lithosphere. (© User:Calistemon / Wikimedia Commons / CC-BY-SA-3.0)
Since Homo sapiens – our human species – emerged in East Africa, it influenced Earth and life on it in many and increasingly profound ways. In the wake of the Cognitive Revolution since around 70,000 years ago, during which humans learned to cooperate efficiently with each other by the usage of language, they expanded all around the globe and were the primary cause of a mass extinction event of large mammalian species, which included all other human species such as Homo neanderthalensis. It is estimated that humans were responsible for the extinction of half of the large terrestrial mammals heavier than 50 kg, while percentages were higher in Australia and the Americas. Human power then again rose during the Agricultural Revolution since around 12,000 years ago, when humans started to domesticate plants and animals and gave up their traditional lives as nomadic hunters and gatherers in order to settle down in newly formed cities, a development which resulted in a human population boom. Around 5000 years ago human societies formed the first bureaucratic states with scribes in the Fertile Crescent, and by 2000 years ago they had already erected mighty empires which ruled over a populace of several tens of millions people spreading over an area of millions of square kilometers, such as the Achaemenid Empire in Iran, the Maurya Empire in India, the Han Empire in China and the Roman Empire in the Mediterranean Basin. Around 500 years ago European seafarers discovered the Americas and circumnavigated the globe for the first time. More profound rises in human power and influences on the Earth, however, took place since around 250 years ago in the wake of the Industrial Revolution in Britain. These influences led researchers to suggest to call the current geological epoch the Anthropocene, which is named after humans and is usually considered to have started either with the Agricultural Revolution, the Industrial Revolution, or the Trinity nuclear detonation of 1945.
While at the end of the Cognitive Revolution the worldwide human population is estimated to have been a few million, due to the Agricultural Revolution in 1 CE the worldwide human population reached about 300 million. The human population stayed relatively stable at this level until about the 14th century CE, after which it slowly increased to 500 million in 1500 and to one billion in 1804, partially due to the dissemination of New World crops and the exploitation of new arable land. Since the 19th century the human population rose more rapidly: In 1927 there were 2 billion people, in 1974 there were 4 billion people, and in 2018 the human populace had again nearly doubled to 7.7 billion people. Two partial reasons for the human population growth in the 20th century were the Haber-Bosch process developed in 1909, by which nitrogen fertilizers could be produced en masse, and the Green Revolution of the mid-20th century which disseminated new agricultural techniques to the developing world. While the maximum population of cities was 1 million since about 1 CE and only a few capital cities ever had reached this level in pre-industrial times – such as Rome in the Roman Empire, Chang’an in the Tang Empire, Baghdad in the Abbasid Caliphate or Beijing in the Qing Empire –, the number of million-sized cities exploded since the Industrial Revolution. New York and Tokyo became the first megacities with urban populations reaching 10 million in the mid-20th century. While 3% of humans lived in urban areas in 1800, in 2010 for the first time in history 50% of humans lived in urban areas: While the majority of humans had been farmers since the beginning of the Agricultural Revolution – feeding a narrow upper class of kings, generals, priests and scribes who are mentioned in the history books –, they now had become city dwellers who worked in factories and offices.
Night view on Earth in 2016. Human settlements are lighting up since the invention of the light bulb in the late 19th century. (© NASA / Wikimedia Commons / Public Domain)
The increased number of humans, together with their advanced technology and their increased power over nature, profoundly influenced the Earth’s lithosphere, atmosphere, hydrosphere and biosphere. Humans extracted large quantities of natural resources from the lithosphere, for example metals such as gold, aluminum, copper, coltan or iron, and the fossil fuels coal, crude oil and natural gas. The metals were used to build tools and cities, and the fossil fuels were usually burned in order to get access to their stored energy – solar energy from a few hundreds of million years in the past. The waste products of burned fossil fuels, in particular the greenhouse gas carbon dioxide, got enriched in the Earth’s atmosphere (rose to more than 400 parts per million which is 50% more than before the Industrial Revolution) and is causing an accelerating anthropogenic global warming (0.6 °C in the 20th century); and the ozone layer in the upper atmosphere, which protects life on Earth from the harmful Sun’s ultraviolet radiation, was weakened in the late 20th century due to the human emission of chlorofluorocarbons (CFCs) which had been widely used as refrigerants. Also the hydrosphere is affected, as the oceans are acidifying due to the intake of carbon dioxide, and sea levels are rising due to the global warming and the melting of glaciers (about 14 cm sea level rise in the 20th century). Also human waste products are accumulating in the oceans, such as in the Great Pacific garbage patch.
Also the modern human influence on the Earth’s biosphere is profound: Today most of the large living animals are living in human captivity. Worldwide there are about a billion sheep, a billion pigs, more than a billion of cattle, and more than 25 billion chickens. Many of them live miserable lives, not having much space, being slaughtered at a young age, and males are usually castrated. More and more wild animals became extinct, numerous forests worldwide were cleared and replaced by farmland, and crops were genetically changed to fit human needs better.
While the exploitation of Earth’s resources and the increased amount of human control over nature, which is based on humanity’s scientific-technological progress, had led to prospering human societies especially since the end of World War II – a time which is characterized by the widespread absence of hunger, diseases and war, and by an exponential increase of human capabilities never seen before –, the Earth’s resources will clearly not sustain ever-growing human populations to the end of time. In view of the foreseeable scarcity of resources it is therefore a challenge for the human societies in the 21st century to use human power wisely and in a responsible way, to treat human as well as animal lives fair and ethically, to avoid a nuclear war which could terminate most of life, and to use the Earth’s resources sustainably.