Hello and welcome back to Extinctions; past, present, and future. Now that we're finally in the present, it's only appropriate that we use extinctions of the geologic past as a guide for defining our place as a species in Earth history. As we discussed, many time units in the geologic time scale are at least partly based on changes in their fossil content, which in turn reflects extinctions and the evolution of new species. The biggest divisions in time units often coincide with mass extinctions. Extinctions help to define epochs, which are subdivisions of periods. But what about extinctions like those of the megafauna that started in the Pleistocene epoch and continued into the Holocene epoch. Are extinctions alone enough to warrant naming a new geological time unit? The short answer is no, or at least not yet. Still, geoscientists have considered naming a new time unit, that recognizes humans as a significant geological and biological force in Earth history. This possible new time unit is referred to as the Anthropocene epoch. The term Anthropocene was formally proposed in 2000 by Nobel Prize winning chemist, Paul Crutuzen, and biologists, Eugene Stoermer. The proposal was published in the International Geosphere-Biosphere program newsletter. Although Stoermer actually started saying Anthropocene as early as 1980. The origin of the word Anthropocene is rooted in anthropo, which means human, and cene, which is a recent epic. But in 1873, more than a century before Stoermer, Italian geologists, Antonius Stoppani, proposed an anthropozoic era. In geologic time units, an era is quite a step up from an epoch, but it reflects that Stoppani was thinking big when it came to estimating the geological impacts of humanity. In 1877, American geologists, Joseph LeConte, proposed a similar psychozoic era, which incidentally, I totally feel like we're in right now. But what he intended with this term was to represent how the workings of the human mind have significantly changed geological systems. In 1920, Russian geologists, Alexsey Pavlov, suggested that the Quaternary period, which encompasses the Pleistocene and Holocene epochs, should be renamed the anthropogene period. So Crutuzen and Stoermer's Anthropocene actually wasn't a new idea, but by the start of the 21st century, it was an idea supported by a lot more evidence. Advocates for officially naming the Anthropocene include geoscientists who point out that humans, through mass agriculture, industrialization, and other actions have changed Earth's systems enough to leave an identifiable signature in the geologic record. The chemists, Crutuzen, identified 1784 as a starting date. Now, that seems really specific, but it's because that's the year James Watt invented the steam engine, which was powered by coal. The advent of humans using extensive fossil fuels led to measurable increases in carbon dioxide, methane, and other pollutants. Today, geoscientists, ecologist, and other environmental scientists point to additional signifiers of the anthropocene. These include agriculture, which led to deforestation and chemical alterations of land and sea environments. Mining, which directly affected landscapes and seascapes and its chemical aftereffects like acid mine drainage. Radioactivity, which we spread by exploding nuclear weapons using nuclear power plants, and producing radioactive waste. The development of new and geologically persistent materials such as concrete, plastics, and metals. The sudden introduction and rapid spread of non-native species with these invasive species causing havoc worldwide, ultimately leading to cats controlling the Internet. Of course, climate change. The rapid rise of human-caused greenhouse gasses, carbon dioxide and methane, from burning fossil fuels has warmed the Earth's atmosphere, melted ice, raised sea levels, and altered weather patterns. Another paleontological justification for naming an Anthropocene epoch is based on extinctions, specifically the megafauna extinctions occurring between 50,000 to 10,000 years ago during the end of the Pleistocene epoch. From a human perspective, 40,000 years is a much broader time span than that represented by the development of agriculture, let alone atmospheric change just over the past few 100 years, or the invention of plastics in the early 20th century. But recall that the end Devonian mass extinction unfolded over several million years. Even the end-Permian took 50,000 to 60,000 years to culminate into the worst mass extinction in Earth history. So it's not much of a stretch to consider human attributed extinctions as one justifier for declaring an Anthropocene epoch. Regardless of what geological signature will designate an Anthropocene epoch, it had to be approved by a committee of geoscientists from the International Stratigraphic Commission. I know, you're already wondering how you can join this commission or at least listen to their podcasts. But it's actually an important scientific group. They review places and times for establishing stratigraphic boundaries, such as between the Paleozoic, Mesozoic and Cenozoic eras. So to study this proposal, the Commission did what any responsible Commission would do. They formed a Sub-Commission called the Working Group at the Anthropocene. The Sub-Commission started work in 2009 and finished in 2016, publishing a peer reviewed articles summarizing their conclusions. The title of this article is about as clear as anyone can expect from a group of academics. The Anthropocene is functionally and stratigraphically distinct from the Holocene. Here's a poetic quote from the article. These distinctive attributes of the recent geological record support the formalization of the Anthropocene as a stratigraphic entity equivalent to other formally defined geological epochs. In other words, new epoch approved. Not all geoscientists fix up to this new epoch though. So for now, you might hold off on throwing your Anthropocene reveal party. But if we have close to 100 percent consensus that the Anthropocene epoch is real and a geological boundary is selected for its start, then we can officially say goodbye to the Holocene epoch. Although megafauna extinctions are a part of the Anthropocene, these extinctions alone do not define it as a geological epoch. As I mentioned, one factor of the Anthropocene was agriculture, which began toward the start of the Holocene, around 11,000 years ago. Has mass agriculture, both the growing of crops and animal husbandry influenced extinction since then? If so, how? After agriculture, came the mining of Earth's resources such as lead ore. In some cultures, this marked the beginning of the development of metal tools and weapons. But these weapons weren't used for killing megafauna, they were used in war for killing and subjugating other people. With war came colonization by Empires. What were the impacts of these pre-industrial human activities, and particularly colonization, on extinctions? That is the topic of our next lecture.
