Mass Extinction

Mass Extinction Students will be able to: • Describe mass extinction. • Identify the five mass extinctions in geological history. • Explain the causes of mass extinctions. Key Vocabulary: Cretaceous, Devonian, Extinction, Mass Extinction, Ordovician, Permian, Triassic Mass Extinction More than 90% of all organisms that have ever lived on Earth are now extinct. Extinction is the process of complete disappearance of a species from Earth. This plays an important role in the evolution of life because it opens up opportunities for new species to emerge. Dinosaurs went extinct about 65 million years ago, after living on Earth for about 165 million years. Mass Extinction During the history of life on Earth, there have been periods of mass extinctions. A mass extinction is a sharp spike in the rate of extinction of species caused by a catastrophic event or drastic environmental change. Mass Extinction Scientists have identified five mass extinctions in Earth’s history. Each mass extinction results in the loss of about 75% of all species in existence across the entire Earth over a “short” geological period of time. Given the vast amount of time since life first evolved on the planet, “short” is defined as anything less than 2.8 million years. Mass Extinction The first mass extinction is called the Ordovician-Silurian Extinction. It occurred about 440 million years ago, at the end of the period Ordovician and followed by the start of the Silurian period. In this extinction event, many small organisms of the sea became extinct. Mass Extinction Scientists theorize that there were two main phases to this extinction — a glaciation event and a heating event. Abundant plant life removed carbon dioxide from the air, causing global cooling and glacier formation. This led to a drop in sea levels, reducing habitats. Mass Extinction Later came global warming and sea level rising again. Creatures that had adapted to the cooler climate were unable to survive the increased temperature. Since most animals was marine at the time, 86% of life was lost. This makes this mass extinction event the second worst mass extinction known to science. An illustration depicting Cameroceras shells sticking out of the mud as a result of draining seaways during the Ordovician–Silurian extinction event. Mass Extinction The next mass extinction is called Devonian extinction, occurring 365 million years ago during the Devonian period. This extinction also saw the end of numerous sea organisms. About 75% of life died off during this period. Tiktaalik, an early air-breathing elpistostegalian, is among the vertebrates which died out. Mass Extinction One theory suggests that land plants developed deep roots, releasing an abundance of nutrients into the oceans that fed algae. Because of this, algae blooms consumed vast amounts of oxygen in the oceans, suffocating many species. Mass Extinction Another theory suggests that another global cooling took place, resulting in glaciation and a fall in sea level, leading to habitat loss. Not only did some creatures go extinct during the late Devonian, but species diversification slowed down during this time. This slowdown may have been caused by the global spread of invasive species. Mass Extinction The largest extinction took place around 250 million years ago. Known as the Permian–Triassic extinction, or the Great Dying. This event saw the end of about 96% of the Earth’s species. Although life on Earth was nearly wiped out, the Great Dying made room for new organisms, including the first dinosaurs. Mass Extinction The Permian-Triassic was the deadliest extinction in history. Scientists believe that volcanic activity in Siberia put massive amounts of carbon dioxide, a greenhouse gas, into the atmosphere. Bacteria that thrive on CO2 began producing methane, another greenhouse gas. Mass Extinction Large quantities of both gases warmed the planet and combined with Earth’s water, making the ocean and rain acidic, creating a highly toxic environment for life. The world’s forest were wiped out and didn’t come back in force until about 10 million years later. This event also wiped-out large numbers of insect species. Mass Extinction Life took a long time to recover from the Great Dying, but once it did, it diversified rapidly. Different reef-building creatures began to take hold, and lush vegetation covered the land, setting the stage for a group of reptiles called the archosaurs – the forerunners of birds, crocodilians, pterosaurus, and the nonavian dinosaurs. Mass Extinction About 210 million years ago, between the Triassic and Jurassic periods, came another mass extinction. By eliminating many large animals, this extinction event cleared the way for dinosaurs to flourish. Some scientists theorize that volcanic eruptions spewed tons of CO2 into the atmosphere, which trapped heat and acidified the oceans, causing this mass extinction. Mass Extinction Other scientists contend that an asteroid or comet impact triggered the extinction. About 80% of life was lost in this extinction, including most of the mammals, making way for the dinosaur’s ancestors. Mass Extinction Finally, about 65.5 million years ago, at the end of the Cretaceous period came the fifth mass extinction. Some 76% of all species on the planet went extinct. This is the famous extinction event that brought the age of the dinosaurs to an end. Mass Extinction The Cretaceous–Paleogene extinction wiped out the dinosaurs, along with 60-76% of all life on Earth. A widely accepted theory is that an asteroid landed in the Yucatan Peninsula in Mexico and killed the dinosaurs. Mass Extinction The impact would have ejected enormous amounts of debris into the atmosphere, causing global temperatures to drop. The impact may have also caused local fires, earthquakes, tsunamis, and acid rain. Mass Extinction Comprehension Check… 1. What role do mass extinctions play in evolution over geologic time? Answer the following questions. 2. Why is the Permian mass extinction also known as the Great Dying? 3. What are some of the causes of mass extinctions? Mass Extinction Comprehension Check… Answers Answer the following questions. 1. What role do mass extinctions play in evolution over geologic time? Mass extinctions opens opportunities for new life to emerge which is an important aspect of evolution. 2. Why is the Permian mass extinction also known as the Great Dying? Permian mass extinction is also known as the Great Dying as it wiped out about 96% of life on Earth. 3. What are some of the causes of mass extinctions? Some causes of mass extinction are catastrophic events and drastic changes in the environment that makes species unable to adapt and survive.