Dominic Corsini has an extensive educational background with a B.S. in Secondary Biology and General Science with a Minor in Environmental Education, an M.Ed. in Educational Leadership, an M.S. in Biology, and a K-12 Principal Certification Program. Corsini has experience as a high school Life, Earth, Biology, Ecology, and Physical Science teacher.
Challenging Societal Norms
Let's begin our investigation into this topic with a simple question. Are dinosaurs, woolly mammoths, mastodons, saber-toothed cats, and giant sloths alive today? The answer is no, of course! Of course they're not still alive, because these species are all extinct.
Extinction occurs when all members of a species have died. And while the idea of extinction may seem commonplace today, during the late 1700's it wasn't a widely accepted concept. George Cuvier (1769-1832) was an anatomist who would challenge this societal norm. While he wasn't the first person to speculate on extinction, he was the first to provide the evidence necessary for establishing extinction as a natural process.
Evidence of Extinction
Georges Cuvier spent a lot of time studying elephant fossils near Paris, France. What he discovered was that elephant fossils differed from the bones of living elephants. The more Cuvier looked, the more differences he found. Cuvier's fossil elephants differed from both Asian and Indonesian elephants, as well as elephant fossils from other parts of the world. Cuvier concluded that these fossilized elephants must represent species that have gone extinct.
While this wasn't exactly a popular opinion initially, Cuvier persisted. He studied more fossils from large animals that could be found living nowhere on Earth. The only logical conclusion pointed toward extinction. But how did extinction occur? Based on fossil evidence, Cuvier suspected that periodic episodes of extinction occurred. He'd established extinction as a fact, but its mechanisms remained a mystery.
After a while, scientists began to uncover the causes for extinction. Though Cuvier would not live to see it, scientists established that approximately 99% of all organisms that have ever lived have gone extinct!
Many of these extinctions occurred slowly, yet every so often Earth would experience a mass extinction. Mass extinctions are when abnormally large numbers of species die out within a limited time frame. The most famous mass extinction event is arguably the extinction of dinosaurs (Cretaceous extinction), yet this is only one of five major mass extinctions in Earth's history (and it's not even the biggest one!). The others include the Ordovician, Devonian, Permian, and Triassic extinctions.
Cause of Mass Extinction
This is where the story of extinction gets really interesting. Why do mass extinctions occur? One idea is known as catastrophism. This is the idea that Earth is occasionally affected by sudden, short-lived, violent events, possibly being worldwide in scope. This is the opposite of uniformitarianism (also known as gradualism), which is defined by more tiny gradual changes in the Earth; in other words, stuff you would never notice day-to-day, like the erosion of a mountain. Catastrophic events change the planet so much that many organisms can't survive. Those organisms die off and new organisms take their place. This is basically why we--mammals--were able to rise to the level that we've reached today!
For example, let's go back to the extinction of dinosaurs. Approximately 65 million years ago a meteorite struck the Earth near Mexico's Yucatan Peninsula (the impact crater has been discovered and is mostly underwater). This impact caused a dramatic shift in climate and ultimately led to the mass extinction of dinosaurs at the end of the Cretaceous period. This mass extinction is an example of catastrophism. Meteorite impacts, ice ages, and ocean acidification are all catastrophic phenomena that can cause mass extinction events. In fact, it's pretty likely that all five major mass extinctions are the result of catastrophism.
George Cuvier was an anatomist who studied the fossilized remains of elephants. He realized that his fossil bones deferred from the bones of living elephants. This led Cuvier to propose that organisms go extinct. Extinction is when no members of a species remain alive. Further investigation into the fossil record led to the realization that Earth experiences periodic mass extinctions. Mass extinctions are when abnormally large numbers of species die out within a limited time. The causes of these extinctions vary, but may all arise due to catastrophism. Catastrophism is the idea that Earth is occasionally affected by sudden, short-lived, violent events that make the planet uninhabitable for many organisms, hence leading to their extinction.
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