Permian–Triassic extinction event ("Great Dying")
The Permian-Triassic extinction event, often referred to as the "Great Dying," occurred approximately 251 million years ago and is considered the most severe extinction event in Earth’s history. It resulted in the loss of around 90% of marine species and 70% of terrestrial vertebrate species due to a combination of volcanic eruptions, climate changes, and oceanic anoxia, which reduced oxygen levels in both the atmosphere and oceans. The volcanic activity, particularly from the Siberian Traps, released large amounts of carbon dioxide and sulfur dioxide, leading to severe environmental shifts, including a greenhouse effect that caused global temperatures to rise dramatically. As ecosystems collapsed, food chains were disrupted, leading to further extinctions.
The extinction event marked the transition from the Permian to the Triassic period, facilitating the emergence of new life forms, including early ancestors of dinosaurs and various marine species such as crabs and lobsters. Recovery of life took approximately 10 million years, during which ecosystems were gradually re-established and diversified. The event serves as a critical point in Earth's biological history, showcasing the resilience of life and the profound impacts of geological and climatic changes over time.
On this Page
Permian–Triassic extinction event ("Great Dying")
The Permian-Triassic extinction event, informally known as the "Great Dying," was a catastrophic series of events that destroyed the majority of life on Earth about 251 million years ago. Scientists have suggested that the extinction event consisted of a combination of immense volcanic eruptions, extreme fluctuations in Earth's climate, and a lack of oxygen in the atmosphere and oceans. Entire populations of plants, reptiles, fish, insects, and mammal-like creatures died in the event. Even animals that survived the initial destruction and attempted to rebuild their ecosystems were later killed by resurgences of Earth's inhospitable atmospheric conditions.
The Permian-Triassic extinction event marked the end of the Permian geologic period and the beginning of the Triassic period. Geologic periods are stages of Earth's history. New types of animals emerged both in the seas and on land in the aftermath of the event. These included ancient crabs, lobsters, marine reptiles, and the four-limbed land reptiles that eventually evolved into dinosaurs.
Background
The Permian period that ended with the Permian-Triassic extinction event was a prehistoric geologic period that began about 299 million years ago. During the Permian period, all land on Earth was united as a supercontinent called Pangaea. The landmass had formed from multiple large land areas known as the continents in modern times. Pangaea covered an immense area of Earth's surface. It featured dramatically different climates in its numerous regions. Much of southern Pangaea was cold and frozen under ice. Rain forests thrived in the hot and humid parts of Pangaea near the equator. The inner section of the supercontinent was intensely hot and dry.
Despite the sometimes harsh climate conditions of Pangaea, many animals prospered during the Permian period. Primitive reptiles lived in the deserts of northern and central Pangaea. As cold-blooded creatures, the reptiles depended on the temperature of their environment to become warm or cold. Daytime temperatures in northern Pangaea could surpass 100 degrees Fahrenheit (38 degrees Celsius) but then drop below freezing at night.
Some reptiles used the sail formations on their backs to catch extra sunlight, while others, known as therapsids, later evolved to become warm-blooded. This means they generated their own heat through their metabolism, the internal chemical processes that sustain life. Therapsids were mammal-like reptiles that evolved into numerous other animal groups throughout the Permian period. Some therapsids became large dinosaur-like creatures. Others were hairy, warm-blooded animals from which modern mammals evolved. Meanwhile, the seas of the Permian period were filled with squid, mollusks, and bony fish. Life in the Permian period flourished for about 48 million years.
Overview
Scientists have proposed several theories to explain the origins of the Permian-Triassic extinction event that began about 251 million years ago. Some scientists suggest the event resulted from a few destructive phenomena that all took place on Earth in a relatively short time, between 100,000 and several million years.
One theory asserts that, over time, the enormous Pangaea blocked the world's oceans from flowing properly. The ocean waters became somewhat stationary and eventually anoxic. Anoxia is the absence of oxygen. The oceans' stagnation also allowed heavy amounts of the gas carbon dioxide to dissolve in the waters. Consequently, the oceans filled with sediment and were similar to a marsh or bog. Since fish survive by taking in oxygen from the water around them, the anoxic state of the world's oceans became poisonous to marine life, and many fish started dying.
Most theories about the Permian-Triassic extinction event also include a series of violent volcanic eruptions that occurred in modern Siberia around the same time as the poisoning of the oceans. These explosions sent lava flowing over millions of miles of land, and the eruptions themselves emitted intense heat, sulfur dioxide, and carbon dioxide into the atmosphere.
The volcanic eruptions caused numerous problems for life on Earth. The sulfur dioxide and carbon dioxide poisoned the air with harmful chemicals. The ash and soot from the explosions also blocked sunlight, preventing plants from being able to grow. The death of most plants disrupted entire food chains. With little greenery to eat, many plant-eating animals died. Large meat-eating predators then had no smaller animals to eat, and they also died.
An additional result of the massive volcanic eruptions was the emergence of the greenhouse effect on Earth. This is the phenomena whereby existing heat becomes trapped in Earth's atmosphere and cannot escape due to the presence of excessive amounts of gases such as carbon dioxide. The greenhouse effect caused the overall temperature of Earth to increase considerably over thousands of years. This global warming initiated extreme weather conditions across Pangaea. Normally humid and rainy areas became dry, and dry deserts became wet. Many animals were unable to adjust to the sudden climate changes and died.
However, the extinction event was not simply one moment in time as, for example, an asteroid impact would be. The initial event took anywhere from tens of thousands to millions of years to complete. Many plants and animals survived the initial destruction and then began repopulating Earth. However, the aftereffects of the main extinction—including resurgent global warming and atmospheric and oceanic anoxia—continued to afflict Earth for another 5 to 6 million years. Animal communities that had survived the first extinction and were now restoring their habitats were suddenly interrupted by these returning destructive waves. The aftereffects of the extinction event ceased after several million years. Life on Earth took about 10 million years to recover fully from the devastation.
The Permian-Triassic extinction event reset Earth's ecosystems. It allowed new animal species to begin flourishing in the seas and on land. Primitive crabs, lobsters, and reptiles filled the oceans. Animals called tetrapods thrived on land. Tetrapods are four-legged animals that include mammals and reptiles. The reptilian tetrapods that emerged several million years after the Permian-Triassic extinction event eventually evolved into the dinosaurs. The dinosaurs remained the largest land vertebrates, or back-boned animals, on Earth for about 165 million years. The impact of a massive asteroid on Earth's surface about 65 million years ago killed most of the dinosaurs.
Bibliography
Bagley, Mary. "Triassic Period Facts: Climate, Animals & Plants." Live Science, 11 Feb. 2014, www.livescience.com/43295-triassic-period.html. Accessed 2 Oct. 2017.
Geere, Duncan. "Earth Took Ten Million Years to Recover from Permian-Triassic Extinction." Wired, 28 May 2012, www.wired.co.uk/article/mass-extinction-recovery. Accessed 2 Oct. 2017.
Ghose, Tia. "Facts about Pangaea, Ancient Supercontinent." Live Science, 17 Dec. 2014, www.livescience.com/38218-facts-about-pangaea.html. Accessed 2 Oct. 2017.
"The Great Dying." NASA, 28 Jan. 2002, science.nasa.gov/science-news/science-at-nasa/2002/28jan‗extinction. Accessed 2 Oct. 2017.
Joel, Lucas. "When Earth Hit the Reset Button on Life: New Research on the Permian-Triassic Mass Extinction." Earth, 25 Oct. 2016, www.earthmagazine.org/article/when-earth-hit-reset-button-life-new-research-permian-triassic-mass-extinction. Accessed 2 Oct. 2017.
Lallanila, Marc. "What Is the Greenhouse Effect?" Live Science, 12 Apr. 2016, www.livescience.com/37743-greenhouse-effect.html. Accessed 2 Oct. 2017.
"Permian Period." National Geographic, www.nationalgeographic.com/science/prehistoric-world/permian/. Accessed 2 Oct. 2017.
"Permian-Triassic Extinction." PBS, www.pbs.org/wgbh/evolution/library/03/2/l‗032‗02.html. Accessed 2 Oct. 2017.
Smith, Roff. "Here's What Happened the Day the Dinosaurs Died." National Geographic, 11 June 2016, news.nationalgeographic.com/2016/06/what-happened-day-dinosaurs-died-chicxulub-drilling-asteroid-science/. Accessed 2 Oct. 2017.