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  • Tens of millions of years ago,

  • a force of nature set two giant masses on an unavoidable collision course

  • that would change the face of the Earth

  • and spell life or death for thousands of species.

  • The force of nature was plate tectonics,

  • and the bodies were North and South America.

  • And even though they were hurdling towards each other

  • at an underwhelming 2.5 cm per year,

  • their collision actually did have massive biological reprocussions

  • by causing one of the greatest episodes of biological migration in Earth's history:

  • The Great American Biotic Interchange.

  • Our story begins 65 million years ago, the beginning of the age of mammals,

  • when what is now North and South America

  • were continents separated by a marine connection

  • between the Pacific and Atlantic Oceans.

  • During this time, South America was the home of fauna

  • that included armored glyptodonts as large as compact cars,

  • giant ground sloths weighing more than a ton,

  • opossums, monkeys, and carnivorous terror birds.

  • North America had its own species,

  • such as horses, bears, and saber-toothed cats.

  • Over 20 million years, the shifting of the Farallon and Caribbean Plates

  • produced the Central America Volcanic Arc, a peninsula connected to North America,

  • with only a very narrow seaway separating it from South America.

  • As these plates continued to surf the Earth's magma layer

  • far beneath the Pacific Ocean floor,

  • the Caribbean Plate migrated eastward,

  • and about 15 million years ago,

  • South America finally collided with this Central American Arc.

  • This gradually closed the water connection between the Pacific and the Caribbean,

  • creating a land bridge,

  • which connected North America to South America.

  • Terrestrial organisms could now cross between the two continents,

  • and from the fossil records,

  • it's evident that different waves of their dispersals took place.

  • Even though plants don't physically move,

  • they are easily dispersed by wind and waves,

  • so they migrated first, along with a few species of birds.

  • They were followed by some freshwater fishes

  • and amphibians,

  • and finally, various mammals began to traverse the bridge.

  • >From South America, mammals like ground sloths and glyptodonts

  • were widly distributed in North America.

  • Moreover, many South American tropical mammals,

  • like monkeys and bats, colonized the forests of Central America,

  • and are very abundant today.

  • South American predator marsupials went extinct 3 million years ago,

  • at which point North American predators, such as cats, bears and foxes,

  • migrated south and occupied the ecological space left behind.

  • Horses, llamas, tapirs, cougars, saber-toothed cats, gomphotheres,

  • and later humans also headed south across the land bridge.

  • But what happened on land is only half the story.

  • What had been one giant ocean was now two,

  • creating differences in temperature and salinity for the two bodies of water.

  • The isthmus also became a barrier for many marine organisms,

  • like mollusks, crustaceans, foraminifera, bryozoans, and fish,

  • and separated the populations of many marine species.

  • It also allowed the establishment of the thermohaline circulation,

  • a global water conveyor belt,

  • which transports warm water across the Atlantic,

  • and influences the climate of the East Coast of North America,

  • the West Coast of Europe, and many other areas.

  • It's a challenge to track all of the ways

  • the collision of the Americas changed the world,

  • but it's safe to say that the ripples of the Great American Biotic Interchange

  • have propagated through the history of life on the planet,

  • and that of mankind.

  • What if these species hadn't gone extinct,

  • or if there were no monkeys in Central America,

  • or jaguars in South America?

  • What if the thermohaline circulation wasn't flowing?

  • Would the East Coast of North America be much colder?

  • It all goes to show some of the most impactful transformations of our planet

  • aren't the explosive ones that happen in an instant,

  • but the ones that crawl towards irreversible change.

  • We are the product of history.

Tens of millions of years ago,

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B2 US TED-Ed america south south america north north america

【TED-Ed】What happens when continents collide? - Juan D. Carrillo

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    Ann posted on 2015/11/29
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