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Speaker 1: Welcome to brain Stuff from How Stuff Works, Hey, brain Stuff,

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Speaker 1: Lauren Vogel bomb Here on the northern coast of the

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Speaker 1: Yucatan Peninsula, near the town of Chichi Lob, Mexico, is

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Speaker 1: a crater about a hundred and twenty miles in diameter.

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Speaker 1: That's about a hundreds The asteroid that created this crater

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Speaker 1: was about six miles that's ten kilometers wide and hit

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Speaker 1: the Earth sixty five million years ago. In spite of

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Speaker 1: these immense measurements, the crater is hard to see, even

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Speaker 1: if you're standing right on its rim. To get a

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Speaker 1: good map, NASA researchers examined it from space. Ten years

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Speaker 1: before the discovery of the Chichi Lob crater, physicist Louise

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Speaker 1: Alvarez and geologist Walter Alvarez, a father son team, proposed

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Speaker 1: a theory about the impact that we know today created it.

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Speaker 1: They noted increased concentrations of the element a ridium in

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Speaker 1: sixty five million year old clay. A Ridium is rare

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Speaker 1: on Earth, but it's more common in some objects from space,

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Speaker 1: like meteors and asteroids. According to the Alvarez theory, a

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Speaker 1: massive asteroid it had hit the Earth, blanketing the world

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Speaker 1: in a ridium. But a shower of particles wasn't the

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Speaker 1: only effect of the collision. The impact caused fires, climate change,

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Speaker 1: and widespread extinctions. At the same time, dinosaurs, which until

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Speaker 1: then had managed to survive for a hundred and eighty

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Speaker 1: million years, died out. Geo Physicist Doug Robertson of the

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Speaker 1: University of Colorado at Boulder theorizes the impact heated Earth's

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Speaker 1: atmosphere dramatically, causing most big dinosaurs to die within hours.

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Speaker 1: This mass extinction definitely happened. Fossil evidence shows that about

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Speaker 1: seventy of species living on Earth at that time became extinct.

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Speaker 1: The massive die off marks the border between the Cretaceous

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Speaker 1: and Tertiary periods of Earth's history, which are also known

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Speaker 1: as the Age of Reptiles and the Age of Mammals, respectively. Today,

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Speaker 1: scientists call the extinction the KT event, after the German

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Speaker 1: spellings of Cretaceous and Tertiary. The KT event had an

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Speaker 1: enormous effect on life on Earth. But what would have

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Speaker 1: happened if the asteroid had missed. Would it have led

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Speaker 1: to a world where people and dine sours would coexist

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Speaker 1: or one in which neither could live? In a world

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Speaker 1: where an asteroid whizzed past Earth instead of crashing down

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Speaker 1: with the force of a hundred million tons of TNT,

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Speaker 1: life could have progressed much differently sixty five million years ago.

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Speaker 1: Some of the animals and plants that are common today

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Speaker 1: we're just getting started. These include placental mammals, which are

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Speaker 1: mammals that develop inside a placenta in the womb, and angiosperms,

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Speaker 1: which are flowering plants. Insects that rely on flowers, such

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Speaker 1: as bees, were also relatively new. Many of these life

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Speaker 1: forms thrived after the KT event, and without that mass

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Speaker 1: reptilian extinction to clear the way, they may not have

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Speaker 1: found ecological niches to fill. In this scenario, today's world

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Speaker 1: might be full of reptiles and short on mammals, including people.

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Speaker 1: But even if the asteroid hadn't hit, dinosaurs and other

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Speaker 1: Cretaceous life forms might have become extinct anyway. Some dinosaur

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Speaker 1: species had started to dwindle long before the asteroids impact.

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Speaker 1: This has led many researchers to conclude that the asteroid

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Speaker 1: was just one spect of a complex story. Other global

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Speaker 1: catastrophes like massive volcanic eruptions in what is now India

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Speaker 1: most likely played a role. Also, the Earth's changing landscape

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Speaker 1: as the supercontinent Pangaea broke up into today's continence probably

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Speaker 1: had something to do with it too. Then, there's another

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Speaker 1: argument that the Chicktullub asteroid hit the Earth too early

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Speaker 1: to have caused the extinction. Researchers GERTA. Keller and Marcus

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Speaker 1: Harding both conclude that the impact took place three thousand

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Speaker 1: years before the end of the Cretaceous period. Keller theorizes

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Speaker 1: the Chicktullub impact was one of at least three massive collisions.

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Speaker 1: Harding argues that the iridium layer didn't come from the

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Speaker 1: Chichillub asteroid, but from another event, such as a series

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Speaker 1: of meteors burning up in the atmosphere. He bases this

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Speaker 1: theory on spheroid particles ejected during the impact. Most of

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Speaker 1: these are in an older layer of the Earth than

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Speaker 1: the Katie irridium layer. According to both of these points

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Speaker 1: of view, the absence of the chick Tallub asteroid strike

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Speaker 1: may not have had a big effect on the Hayti extinction.

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Speaker 1: Earth was a warm planet for most of the time

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Speaker 1: that dinosaurs lived. After the end of the Cretaceous period,

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Speaker 1: the world got a lot colder and experienced several ice ages.

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Speaker 1: Whether dinosaurs could have survived such a change in climate

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Speaker 1: is debatable. It's hard to come to a definitive conclusion

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Speaker 1: about what the world would look like today without the

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Speaker 1: Chick to Love impact, but the question of whether people

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Speaker 1: and dinosaurs could have coexisted is a captivating one. The

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Speaker 1: idea is present in everything from the congo legend of

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Speaker 1: mokol Ambenbe to King Kong to the pervading kitch of

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Speaker 1: the Flintstones. Then, of course, there's the prevailing scientific theory

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Speaker 1: about the origin of birds that they are, in essence,

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Speaker 1: dinosaurs that we are coexisting with today. Today's episode was

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Speaker 1: written by Tracy V. Wilson and produced by Tyler Klang.

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Speaker 1: Brain Stuff is a production of I Heart Radio as

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Speaker 1: How Stuff Works. To hear more from Tracy, check out

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Speaker 1: the podcast Stuff You Missed in History Class, and for

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Speaker 1: more on this and lots of other historic topics, visit

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Speaker 1: favorite shows.