The Holocene Extinction

Gabriela Petic

Dr. Riu de Sousa

101-NYA-05 gr. 00006

14 May 2018

The Holocene Extinction

        A mass extinction is defined by dictionary.com as the “extinction of a large number of species within a relatively short period of geological time, thought to be due to factors such as a catastrophic global event or widespread environmental change that occurs too rapidly for most species to adapt.” Previously, there were five mass extinctions: the ordovician mass extinction, the devonian mass extinction, the permian mass extinction, the triassic mass extinction, and the cretaceous mass extinction. Right now, the world is facing yet another mass extinction, perhaps the greatest one of all time: the holocene mass extinction. This extinction is quite unique from all the others because not only is it arguably the fastest but it is also caused only by human activity. It is important to inquire furthermore information on the subject in order to improve our current situation and try to slow down the inevitable disaster. It is important to know about the holocene’s origin and its predecessors, the current climate change enhanced by humans, and how to decelerate this extinction.

In order to fully understand the importance of this current extinction, it is important to look at the five past ones. The first one occurred during the Ordovician Period, which lasted around 45 million years. It started 488.3 millions of years ago, and it ended 443.7 million years ago. During this period, most of the earth was ocean. The Ordovician era is mostly recognized for its diverse marine invertebrates. From the Lower to Middle Ordovician the climate was relatively mild, the weather was warm and the atmosphere contained a lot of moisture. During Upper Ordovician period, massive glaciers were formed, which caused the drainage of shallow seas and the level of deeper seas dropping drastically. This was likely the cause of the first mass extinction which caused 60% of the marine invertebrates and 25% of all species to disappear. As the earth slowly recovered from the first massive extinction, new species appeared and the first plants and insects developed. This marked the beginning of the Devonian period which lasted around 63 million years. It began 417 million years ago and it ended 358 million years ago. These plants then contributed to the second mass extinction because they absorbed enough carbon dioxide that it created another round of global cooling. This global cooling then changed the soils which caused nutrients to wash into the ocean that, in turn, created so much algae which sucked up so much of the oxygen that it essentially choked most animal species to death. In that extinction 70% of animal species were wiped out along with 19% of their whole families. The third mass extinction was by far the most destructive out of them all. It occurred during the latter part of the Permian Period. The Permian Period lasted around 48 million years. It started 299 million years ago and it ended 251 million years ago. During this period most species that survived the Devonian extinction evolved into reptiles, amphibians and most of all the land animals we know today. This extinction was most probably caused by volcanic activity that destroyed the ozone layer, which in turn, caused the average temperature to increase up to 40 degrees Celsius. Because of this incredibly high average temperature, there were acid rains which destroyed mostly all life on land. In this extinction 70% of all land species and 90% of all marine species were lost. The fourth mass extinction took place during the Triassic Period. This Period started 252 million years ago and it ended about 201 million years ago, thus making it last roughly 51 million years. During that period, the earth was colonized mostly by early small dinosaurs. During that time, a volcanic rift split up the land in half, thus creating the Atlantic ocean. Unfortunately the volcanic activity that happened under water released carbon dioxide which killed off about 80% of the species that existed at that time. Surprisingly, dinosaurs evolved fairly well in that new somewhat deserted world, and they continued to prosper over the next couple million years. This marked the Jurassic era, which began 199.6 million years ago and ended 145.5 million years ago. Many people believe that the next mass extinction was caused by an asteroid crashing into what is now Mexico’s Yucatan peninsula. This asteroid, contrary to common belief, did not immediately kill all the dinosaurs, instead the dust particles blocked out the sun which caused the bigger dinosaur species to slowly die, followed by the smaller ones. The small dinosaurs that survived later evolved into what we know as birds. This extinction killed off approximately 75% of species. Now, the world is facing yet another mass extinction, but this time it is much more fast and destructive than all the previous ones. The rate of the Holocene extinction is believed to be between 100 and 1000 times faster than all the past extinctions(Wagler, p.4).The Guardian says that, “Nearly half of the 177 mammal species surveyed lost 80% of their distribution between 1900 and 2015.” This quickened rate is believed to be due to human activity. In fact, carbon dioxide levels have climbed up at least 25% in the last fifty years, all due to urbanisation, pollution and industrialisation. Many species were also completely wiped out solely by fishing, hunting, habitat destruction and simply pollution. Although the Holocene mass extinction isn’t only caused by humans, they are the prime reason why it is happening so incredibly fast.

One of the reasons why the Holocene mass extinction is so fast is because of all the climatic changes that have happened and are still happening. Humans learning how to grow food and practicing agriculture have introduced newer means of climate change, pollution, and ecological development. Industrial agriculture is responsible for a staggering amount of carbon dioxide emissions. Collin Dunn says in his article 6 Ways agriculture Impacts Global Warming, that “The U.S. food system contributes nearly 20 percent of the nation’s carbon dioxide emissions; on a global scale, figures from the Intergovernmental Panel on Climate Change (IPCC) say that agricultural land use contributes 12 percent of global greenhouse gas emissions.” These percentages are true if we only take agriculture itself into account, but according to Will Allen, the use of pesticide, fertilizers,fuel and oil for tractors, equipment, shipping, trucking, electricity, and emissions of carbon dioxide, methane, nitricious oxide and other green gases bump the impact up to 30% of the U.S. collective carbon footprint. In The Sixth Extinction, Elizabeth Kolbert says that, “ since the nineteenth century industrial revolution, our ever-increasing level of fossil fuel, combustion and deforestation has raised the level of greenhouse gases in the air by 40%, with a 6% increase in carbon dioxide per year [...] computer modelling has calculated that a doubling of carbon dioxide in the atmosphere would lead to an irreversible increase in global temperature around 3 degrees Celsius above what it was in the 1950s, (p.108).” Kolbert also says that even small increases in CO2 levels would have three major effects. The first one would be the melting of the north and south poles, since carbon dioxide dissolves water and that would create massive difficulties for the species that depend on ice and coral reefs in order to survive. The second effect comprises putting our own species and social order in danger since many animals are predicted to die or migrate when their resources are all drained and their homelands destroyed. The third effect caused by anthropogenic climate change could be the destruction of the earth as a habitable planet. The world’s forests influence climate in many ways. The complex forest-atmosphere interactions can dampen or amplify anthropogenic climate change. One of the main reasons why deforestation is an important factor of climate change is because forests are known to absorb CO2 and transform it into oxygen through photosynthesis. As Wagler mentions in The Sixth Great Mass Extinction, “approximately 75% of temperate forests, Mediterranean forests, and temperate grasslands have been replaced by cultivated land,” (p.3). Cutting out entire forests leads to more carbon dioxide in the atmosphere that is not turned into oxygen, which in turn, increase the overall temperature. It is also estimated that due to cutting and burning of forests every year, more than 1.5 billion tons of carbon dioxide are released into the atmosphere. Not to mention, that the destruction of forests is directly responsible for the extinction of many animal species every year since their habitat and resources are demolished.