Introduction
All living beings form ecosystems with many internal and external connections; ecosystems are assembled into a single biosphere. This global system of life is in constant dynamic equilibrium. The colossal complexity of the biosphere compensates for any negative impact. However, sometimes ecosystems collapse, such a catastrophe can last from several millennia to millions of years. Each mass extinction is a unique event with its own set of causes. Furthermore, in the near future, humanity may become such a reason.
Geologic History of the Earth
In the history of our planet, there have been five mass extinctions. There are the Ordovician-Silurian (450-443 million years ago), Devonian (372 million years ago), Permian (253-251 million years ago), Triassic (208-200 million years ago), and Cretaceous-Paleogene (65.5 million years ago). In the course of the Ordovician-Silurian extinction, almost 85% of all species, which inhabited the planet died (“Mass extinctions”, 2017). The Ordovician-Silurian extinction had two stages in one million years. It is believed that the reason for the former was the movement of the ancient supercontinent of Gondwana towards the South Pole and the latter – the global warming. The trilobite family trinucleidae, brachiopod genus thaerodonta, brachiopod genus plaesiomys and others disappeared from this period.
The Devonian extinction occurred over a long period, during which there were three disasters, each separated by 10 million years. Since the dyed species of creatures were mainly from tropical groups, the reason for it could be climate change due to a decrease in the amount of carbon dioxide in the atmosphere (“Mass extinctions”, 2017). Extinct groups of species were the odontopleurid trilobites, dalmanitid trilobites, phacopid trilobites, atrypid brachiopods, and pentamerid brachiopods.
The Permian extinction was the worst event that ever happened on the Earth. Within 60 thousand years, 96% of all marine and about 70% of terrestrial species became extinct, which is why the restoration of the biosphere took a much longer time, and all ecological ties were destroyed (“Mass extinctions”, 2017). It is believed that the most probable reason was increased volcanic activity in Siberia, which has result in global warming. The tabulate corals, rugose corals, goniatitic cephalopods, productid brachiopods, and cladid crinoids disappeared from this period.
The Triassic extinction consisted of the eruption of volcanoes, which occurred because of the disintegration of the supercontinent of Pangea. For that reason, a considerable amount of carbon dioxide got into the atmosphere of ancient Earth, which could radically change the planet’s climate and kill living beings. Shelled cephalopods, brachiopods, corals, sponges on the ocean, and phytosaurs, crocodile-like animals on the land, were hard hit.
Cretaceous is the most recent mass extinction, destroyed 75% of all species, including dinosaurs. It hastened the evolution of mammals and the emergence of man. According to the most common version, the catastrophe was a falling meteorite about 10 kilometers in size. The impact in the first stage caused massive fires, earthquakes, and giant tsunamis on Earth (“Mass extinctions”, 2017). The non-avian dinosaurs, vertebrates, plesiosaurs, ichthyosaurs disappeared.
When animals began to share the planet with a new biological species – Homo sapiens – the habitat for them became many times more hostile. The successful adaptation of humans to the environment often resulted in the extinction of other species. In particular, the steller cow belonged to the group of sirens. These animals were not afraid of man because they never encountered him (“Extinctions in the recent past and the present day”, 2017). Consequently, of the mass capture of steller cows, less than 30 years have passed since they were finally exterminated.
Bird watchers estimate that the population of wandering pigeons numbered 3-5 billion birds, the species was the most abundant, accounting for a third of all terrestrial birds in the United States. Tasty meat and ease of catching made them the primary niche for poultry meat production and consumption. As a result, billions of wandering pigeons first turned into millions, and then they were utterly exterminated by man.
Global Climate Change
The Earth’s atmosphere allows sunlight to pass through while retaining thermal radiation from the surface. The accumulation of gases and other emissions in the atmosphere aggravates this process, triggering the greenhouse effect (“A blanket around the Earth”, n.d.). This global problem has existed for a long time, but it becomes more relevant to developing technologies. Greenhouse gases are the collective name for a whole set of gases that can trap the planet’s thermal radiation. In the visible range, they remain transparent while absorbing the infrared spectrum. The leading greenhouse gases are water vapor, carbon dioxide, methane, nitric oxide, and chlorofluorocarbons.
The reason for the greenhouse effect is the rapid growth of an industry that uses oil, gas, and other fossil hydrocarbons as energy sources; they account for about half of all gas emissions. Apart from it, in the process of photosynthesis, trees assimilate carbon dioxide and produce oxygen; forests are the “lungs of the planet,” their destruction is fraught with a sharp increase in the amount of carbon dioxide in the atmosphere (“A blanket around the Earth”, n.d.). As a result of the decay of farming animals’ waste products, a large amount of methane is formed, which is one of the most aggressive greenhouse gases.
The scientists came to a conclusion about the possibility of a sixth extinction. The critical factors of the destruction of 145 scientists from 50 countries in their report named, in particular, changes in land use, hunting, climate change, environmental pollution. According to the researchers, due to human activities, 75 percent of the land, 40 percent of the world’s oceans, and 50 percent of river waters are already actively degrading (Díaz et al., 2019). Since the 16th century, at least 680 species of vertebrates have become extinct. According to average estimates for all groups of plants and animals, extinction now threatens 25 percent of species. More than 40 percent of amphibians, 33 percent of reef corals, and more than a third of marine mammals are at risk. Extinction threatens 10 percent of insect species, and if the trend continues, by the end of the century, they may not remain on Earth at all. In summary, all this will radically change the entire biosphere of the planet.
Conclusion
To summarize, all cases of mass extinction have left their mark on the history of life on the planet. According to many sources, today, the Earth is experiencing another catastrophe associated with human activities. People have become a factor that changes the evolutionary fate of other earthly creatures. Nonetheless, understanding the past processes and a responsible attitude to nature and drawing attention to the current ecological situation can help preserve the biosphere.
References
A blanket around the Earth. (n.d.). National Aeronautics and Space Administration. Web.
Díaz, S., Settele, J., Brondízio, E. S., Ngo, H. T., Guèze, M., Agard, J., Arneth, A., Balvanera, P., Brauman, K. A., Butchart, S. H. M., Chan, K. M. A., Garibaldi, L. A., Ichii J. Liu, K., Subramanian, S. M., Midgley, G. F., Miloslavich, P., Molnár, Z., Obura, D., Pfaff, A, … Zayas, C. N. (2019). Summary for policymakers of the global assessment report on biodiversity and ecosystem services of the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services. The Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services. Web.
Extinctions in the recent past and the present day. (2017). Sam Noble Museums. Web.
Mass extinctions. (2017). Sam Noble Museums. Web.