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The most direct evidence of extinction is seen in fossils that are plentiful in older rocklayers but scarce in the more recent ones. From tiny marine amphibians to enormous mammals, avast variety of animals and plants are susceptible to rapid extinction. Species become extinct on acontinuous basis. Mass extinctions, are the most widespread and catastrophic loss of biodiversity ina relatively short period of time. Today, 5 mass extinctions in Earth's history have been identified byscientists.
Ordovician-Silurian Extinction is the planet's first mass extinction event. Occurred 443million years ago, a majority of marine life perished. Sea temperatures changed as a result of adramatic climate shift. Glaciation on a global scale trapped large amounts of water and drastically reduced global sea levels. Many species' essential habitats have been destroyed, along with damaged food chains and decreased reproductive success.
Following the Devonian Extinction 359 million years ago, numerous tropical marine animals became extinct. Plants' roots altered the terrain they lived on, converting rock and rubble into soil. Following the runoff of this nutrient-rich soil into the world's oceans, massive "dead zones" of algae were produced, stifling marine life and destabilizingmarine food networks. Unable to adapt to the reduced oxygen levels and absence of food, manyspecies disappeared.
Permian-Triassic Extinction is the largest mass extinction event in Geologic time,wiping out roughly 95% of marine and 70% of terrestrial species. Volcanoes emitted a massive amount of carbon dioxide into the atmosphere, generating agreenhouse effect that warmed the globe. Carbon dioxidelevels in the ocean have significantly increased and wiped outmany marine life by depriving them of oxygen-rich water.
The Triassic-Jurassic Extinction between 252million and 201 million years ago wiped out other vertebratespecies on land, allowing dinosaurs to thrive. Volcanoesreleased massive volumes of carbon dioxide, similar to the Permian Extinction, forcing climate change and destroying life on Earth. Ice melted, sea levels rose,and the oceans became acidic as global temperatures soared.
The most well-known mass extinction event is the Cretaceous-Tertiary Extinction,which occurred around 66 million years ago and was responsible for the extinction of dinosaurs. Anasteroid over 8 miles large at 45,000 mph crashed on Earth after landing in what is now Yucatán,Mexico. Following the collision, months of darkening skies were caused by debris and dust beingcast into the atmosphere. This stopped plants from absorbing sunlight, causing them to die indroves and disrupting the dinosaurs' feeding chains. It also caused global temperatures to plunge,throwing the planet into an extended frigid winter.
A sixth mass extinction, according to many biologists, is currently taking place. This isdue to the outcome of people damaging and deteriorating other species' habitats. The extinction isconsidered to have started around 50,000 years ago with the advent of humans in Australia and theAmericas. In the coming decades, one in four species of known mammals and one in eight speciesof known birds face extinction. If current trends continue, humanity may lose half of all known livingspecies by the end of the century.
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