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(animals cawing)

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66 million years ago, something from space

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slammed into Mexico's Yucatan Peninsula.

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And it caused a mass extinction.

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The Chicxulub impact killed 75% of life on Earth

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and ended the reign of the dinosaurs.

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I think we kind of identify with those dinosaurs.

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(dinosaur roaring)

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They reigned for Earth for 100 million years

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and then they were gone.

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Could that happen to us?

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Dr. David Kring is a senior scientist

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at the Lunar and Planetary Institute in Houston, Texas.

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It's managed by the University Space Research Association.

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The planetary geologist was on the team

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that first identified the crater from this impact.

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In Haiti, we found a very large,

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nearly half meter thick deposit of impact debris

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that he been ejected from the crater.

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That deposit told us that somewhere in the Gulf of Mexico

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was where the impact occurred.

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Dr. Mark Boslough was a physicist

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at the Los Alamos National Laboratories in New Mexico.

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And a professor at the University of New Mexico.

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He's an expert on cosmic impacts and air bursts.

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Impact craters on the Earth are generally a lot bigger

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than the asteroid that created them.

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The crater can be something like eight times

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the diameter of the asteroid or it can be

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up to 16 times the diameter of the asteroid.

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At the time of the Chicxulub impact,

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Earth's geography was slightly different.

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Sea levels were generally higher.

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Today, when you actually draw a circle on the map

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of where the Chicxulub crater is, it appears to be

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straddling the coastline of the Yucatan Peninsula.

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But the Yucatan Peninsula was completely submerged

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at the time of the impact.

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That means that areas in Texas were also underwater.

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Because the crater is underwater,

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and because natural processes have further concealed it,

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determining the size of the impactor

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that created it wasn't easy.

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And so today, it is completely buried.

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We have to drill about a kilometer beneath the surface

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before we reach the impact crater.

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It was revealed that the Chicxulub crater

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is approximately 110 miles wide.

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And that the Chicxulub asteroid was about six miles across.

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(suspenseful music)

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Mark Boslough has created some of the most revealing

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simulations of an impact.

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When we do a simulation of an impact

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on the surface of the Earth, the composition of the impactor

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determines whether it breaks up in the atmosphere

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or whether it hits the surface.

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The asteroid displaces the air

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in front of itself, creating a hole in the atmosphere.

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And that creates a plasma and that plasma is hot

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and it radiates light and heat and that actually

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heats up the asteroid and causes it to vaporize.

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One big asteroid impact can change

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our planet forever, as it did then.

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When an impacting object hits the Earth's surface,

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it's moving very fast.

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It can vaporize a portion of the Earth's crust

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as well as the object itself and jack it up

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to super heated temperatures, to a plasma.

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So this material might reach temperatures

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of say 10,000 degrees.

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This is the temperatures that we normally

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associate with the sun.

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Before the air can rush back in,

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vaporized rock is ejected 60 miles skyward.

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That's more than 10 times the height of Mount Everest.

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Next, an impact of this size produces tsunami waves

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at least 300 feet tall.

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Tsunamis that radiated across the Gulf of Mexico

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right over the area that we now call Houston

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and penetrated far inland, halfway to Dallas at least.

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As the tsunamis flood the land,

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the vaporized asteroid continues to displace air and water.

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Choking hot dust thickens the skies.

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(dinosaur roaring)

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And fires erupt wherever there are trees.

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Something on the order of 10 trillion metric tons

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of material came raining back down through the atmosphere.

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The Chicxulub asteroid was unstoppable.

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And if a similar one hit today, we'd be in big trouble.

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I wish I could say how humans would fare

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in an impact on the order of Chicxulub.

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I doubt if they would fare any better than the dinosaurs.

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Over the last 600 million years,

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Earth's been hit more than 60 times by space rocks

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at least three miles in diameter.

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Tons of spaces rocks hit us daily,

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dust sized mostly, and they do no damage.

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But when impactors get large and punch through

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the atmosphere to reach Earth's surface,

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then Houston's got a problem.

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Today, the Port of Chicxulub Puerto lies almost exactly

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at the geographic center of the crater.

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If the asteroid or comet hit the same place today,

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the tiny town would instantly vanish

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as though it never existed.

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(dramatic music)

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When a six mile impactor, traveling at perhaps 35,000

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miles per hour hits a solid target,

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the kinetic energy is measured in megatons.

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Chicxulub impactor had a kinetic energy,

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we think, of about 100 million megatons.

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The earliest atomic bombs that were developed

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by the Manhattan Project and set off here in New Mexico

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were 10 to 20 kilotons.

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So we're talking about 10 billion atomic bombs

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all going off at once.

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The bomb that decimated Hiroshima

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in 1945 destroyed reinforced concrete buildings

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up to half a mile from ground zero.

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That's the damage from an asteroid only as large

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as an average sized house.

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The Chicxulub impactor was 120 city blocks across.

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If one hit in the same place today,

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everything within a 1,500 mile radius

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would instantly be destroyed, including Houston.

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So if that impact event were to occur today

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in a similar water setting,

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those same types of tsunamis would be generated.

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In the vicinity of Houston, the tsunamis might be

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50 meters, 100 meters high.

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And that is a big wave.

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With skyscrapers that reach 200 meters tall,

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a wave of this magnitude would climb as high as 50 stories

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and wipe out the city.

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I invite anybody to step outside their home

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and imagine a wall of water 100 meters high

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sweeping through their neighborhood.

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And it has global consequences, which as the name implies,

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has an effect everywhere else on the world.

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Within the first 12 to 24 hours,

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Earth's global atmosphere will approach the temperature

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of a microwave oven.

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This happens with a big impact,

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whether it hits the ground or not.

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But if it explodes in the atmosphere,

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it still does damage to the surface.

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It can still wipe out a city.

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It can still hurt people.

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And if it's big enough, it just completely vaporizes

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and incinerates everything in its path.

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That's what an air burst can do.

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Dust and debris obscure the sun,

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so across the globe, plants that rely

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on photosynthesis will die.

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Temperatures quickly drop by at least 40 degrees worldwide.

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An asteroid this size kick starts an ice age.

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A large impact also causes earthquakes.

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The blast wave hits the ground and that causes

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the ground to shake.

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Rock layers will be pulverized.

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Buildings and highways will disintegrate.

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If we had advanced warning, people would crowd

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into the deepest available spaces in their towns or cities.

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Safe underground for a brief window.

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But regardless of where it hits,

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95% of the world's population will be dead

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within 24 hours from one or more effects of the aftermath.

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If tomorrow's asteroid hits the Yucatan again

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and not elsewhere, the catastrophe will be magnified.

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Scientists discovered that the target rocks in Chicxulub

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contain large amounts of sulfur.

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Sulfur in the asteroid combines with sulfur in the ground

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to create a particularly toxic soup when it rains.

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Greenhouse warming gases will remain in the atmosphere

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for decades or even centuries.

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Without plants and plankton to maintain a balance,

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carbon dioxide levels increase further.

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For this global catastrophe to occur today,

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we wouldn't need a monster asteroid.

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Even a much smaller impactor would be disastrous for us.

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The greatest risk is actually in the smaller ones,

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the ones that are gonna kill a few people,

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the ones that might wipe out a city, the small ones

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and that's because there's so many more of them.

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They're so much more probable.

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It's impossible to predict

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where an asteroid will hit, how large it will be,

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and what it will mean to us.

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But with nearly 800,000 asteroids identified

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in our solar system, the experts say if it's not a question

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of if we'll be hit again, but when.

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'Cause we have a very limited time window

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in which to come together and minimize the damage to us

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and prevent a global catastrophe.

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We think of planetary defense as just mitigation,

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as deflecting an asteroid that may be on a collision course,

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but it's also preparing for one that we don't expect,

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that we don't see coming,

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or we don't see coming until the very last minute.

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We may have ideas of what lurks out there,

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but it would be folly to say we know what lurks there.

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If we discover something a few days before impact,

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well it's on its final approach.

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It's on its what we call death plunge.

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We can't deflect it, there's nothing we can do about it.

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NASA and organizations around the world

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vigilantly watch the skies for any potential threats.

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Some asteroids are so dark that they're nearly invisible.

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Solutions to a future impact are still

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in the theoretical stage, however, they all require

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some advance warning.

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One audacious idea, flying a spacecraft at full speed

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right into an asteroid.

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The force of the impact would then deviate the object

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a few centimeters, enough to potentially change

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its trajectory and allow it to fly right past Earth.

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We now understand impact cratering processes

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can alter not only the geologic evolution of Earth

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but the biologic evolution of planet Earth.

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In the mean time, the vast crater in Mexico

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is a reminder of both our fragility and our ability

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to solve even the most insurmountable problems.

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(dramatic music)