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  • From damming rivers to changing the chemistry of the atmosphere, humans have had a powerful

  • impact on our planet. But what would happen if we suddenly disappeared?

  • The first few weeks would be chaotic. Within hours, power plants would run out of fuel

  • and shut down. As lights go out and electric fences lose their sting, over one and a half

  • billion cows, nearly a billion pigs and more than 20 billion chickens will break out of

  • their enclosures, desperate for food. Without any humans to feed them, most of these livestock

  • will starve or become food for over half a billion dogs and a roughly equal number of

  • cats who now have to fend for themselves. Of course, many of our fancy breeds are ill-suited

  • for life in the wild, and will probably be outcompeted by hardier mutts, not to mention

  • wolves, coyotes and wildcats. Other animals that depend on humans, from rats to cockroaches,

  • will suffer drastic population declines. Some, like body lice and head lice, will go extinct.

  • In the cities, many of our famous boulevards are now rivers. Without electric pumps to

  • keep them dry, underground subway tunnels will

  • quickly fill with water. Other streets will be overtaken with weeds and vines, followed

  • by larger plants and trees.

  • But before that happens, most cities will be wiped out by fire. Modern houses, especially

  • in the suburbs, are still largely made of timber. With no firefighters around, a single

  • lightning strike is all it takes to start a fire that could burn whole subdivisions

  • to the ground. In the countryside, many wood structures will be destroyed within a few

  • decades, if not by fire, then by termites and other decomposers.

  • After 100 years most wood structures will be gone, and anything made of steel - from

  • apartment buildings to cars and even bridges - aren’t

  • far behind. Steel is mostly iron, and without constant

  • application of paints and coatings, it will quickly react with oxygen in the atmosphere

  • and return to its native form of iron oxide, or rust.

  • By this time humans have been gone for a few hundred years, and most species of animals

  • around the world - at least, the ones we haven’t driven to extinction - will have bounced back

  • to the levels they were at before we evolved.

  • But their distribution will remain forever altered.

  • Camels now roam Australia, while in North America dozens of species of songbirds imported

  • from Europe will continue to thrive. It’s even possible that in some parts of the world,

  • escaped zoo animals could form new wild populations, leading to the prospect of lions on the Great

  • Plains, or hippos in South American rivers.

  • Forever proliferating through space will be the electromagnetic radiation we created from

  • our radios, satellites and phones.

  • But if anything will outlast us on Earth, it may be our trash. The chemical bonds that

  • hold together plastics or vulcanized rubber are immune to most of the digestive enzymes

  • used by bacteria to break down natural polymers and unlike metals, plastics don’t rust or

  • corrode. These microplastics escape into waterways or drift along in the ocean and are eventually

  • deposited in sediments. Hundreds of millions of years from now, alien geologists from outer

  • space may be surprised to find sedimentary rocks full of tiny carbon-based particles

  • that were once part of rubber tires or plastic bags.

  • Of course, whether something survives depends greatly on the conditions. Everything will

  • last much longer in deserts, where there is no

  • moisture to speed up rusting or support decomposing organisms. And while the carbon cycle will

  • return CO2 levels to equilibrium after a few thousand years, local deposits of long-lived

  • organic chemicals or radioactive material could persist for a very, very long time.

  • It’s hard to know what alien paleontologists of the future will make of us; how they will

  • explain our love of plastic or the fact that within

  • a geological eyeblink we exploded out of Africa to

  • colonize virtually every inhabitable space on earth. But theyll definitely wonder

  • why, if we were so successful for so long, we disappeared

  • so quickly.

  • This episode is brought to you by Squarespace.com. If youve ever wanted to make your own website,

  • Squarespace recently launched the latest version of their platform, Squarespace 7, which has

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  • and if you decide to sign up, use the offer code ASAP at checkout to get 10% off. Thanks

  • again to squarespace for supporting our show.

  • And if you haven’t seen our latest AsapTHOUGHT video on Why We Mishear Lyrics, you can check

  • that out with a link in the description as well - it should give you a good laugh and

  • hopefully help solve some mysteries of your brain on music.

  • And subscribe for more weekly science videos!

From damming rivers to changing the chemistry of the atmosphere, humans have had a powerful

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What If Humans Disappeared?

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    Jason Hsiao posted on 2015/02/02
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