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  • About 66 million years ago, something terrible happened to life on our planet.

  • Ecosystems were hit with a double blow as massive volcanic eruptions filled the atmosphere with carbon dioxide and an asteroid roughly the size of Manhattan struck the Earth.

  • The dust from the impact reduced or stopped photosynthesis for many plants,

  • starving herbivores and the carnivores that preyed on them.

  • Within a short time span, three-quarters of the world's species disappeared forever,

  • and the giant dinosaurs, flying pterosaurs, shelled squids, and marine reptiles that had flourished for ages faded into prehistory.

  • It may seem like the dinosaurs were especially unlucky,

  • but extinctions of various severities have occurred throughout the Earth's history, and are still happening all around us today.

  • Environments change, pushing some species out of their comfort zones while creating new opportunities for others.

  • Invasive species arrive in new habitats, outcompeting the natives.

  • And in some cases, entire species are wiped out as a result of activity by better adapted organisms.

  • Sometimes, however, massive changes in the environment occur too quickly for most living creatures to adapt,

  • causing thousands of species to die off in a geological instant.

  • We call this a mass extinction event,

  • and although such events may be rare, paleontologists have been able to identify several of them through dramatic changes in the fossil record,

  • where lineages that persisted through several geological layers suddenly disappear.

  • In fact, these mass extinctions are used to divide the Earth's history into distinct periods.

  • Although the disappearance of the dinosaurs is the best known mass extinction event,

  • the largest occurred long before dinosaurs ever existed.

  • 252 million years ago, between the Permian and Triassic periods,

  • the Earth's land masses gathered together into the single supercontinent Pangaea.

  • As it coalesced, its interior was filled with deserts,

  • while the single coastline eliminated many of the shallow tropical seas where biodiversity thrived.

  • Huge volcanic eruptions occurred across Siberia, coinciding with very high temperatures, suggesting a massive greenhouse effect

  • These catastrophes contributed to the extinction of 95% of species in the ocean,

  • and on land, the strange reptiles of the Permian gave way to the ancestors of the far more familiar dinosaurs we know today.

  • But mass extinctions are not just a thing of the distant past.

  • Over the last few million years, the fluctuation of massive ice sheets at our planet's poles has caused sea levels to rise and fall,

  • changing weather patterns and ocean currents along the way.

  • As the ice sheets spread, retreated, and returned,

  • some animals were either able to adapt to the changes, or migrate to a more suitable environment.

  • Others, however, such as giant ground sloths, giant hyenas, and mammoths went extinct.

  • The extinction of these large mammals coincides with changes in the climate and ecosystem due to the melting ice caps.

  • But there is also an uncomfortable overlap with the rise of a certain hominid species originating in Africa 150,000 years ago.

  • In the course of their adaptation to the new environment, creating new tools and methods for gathering food and hunting prey,

  • humans may not have single-handedly caused the extinction of these large animals, as some were able to coexist with us for thousands of years.

  • But it's clear that today, our tools and methods have become so effective that humans are no longer reacting to the environment, but are actively changing it.

  • The extinction of species is a normal occurrence in the background of ecosystems.

  • But studies suggest that rates of extinction today for many organisms are hundreds to thousands of times higher than the normal background.

  • But the same unique ability that makes humans capable of driving mass extinctions can also enable us to prevent them.

  • By learning about past extinction events, recognizing what is happening today as environments change,

  • and using this knowledge to lessen our effect on other species,

  • we can transform humanity's impact on the world from something as destructive as a massive asteroid into a collaborative part of a biologically diverse future.

About 66 million years ago, something terrible happened to life on our planet.

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B1 US TED-Ed extinction mass extinction massive environment earth

【TED-Ed】When will the next mass extinction occur? - Borths, D'Emic, and Pritchard

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    E posted on 2021/08/13
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