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What Killed the Dinosaurs?

Dinosaurs roamed the Earth for 135 million years. Filling every ecological niche, from the oceans, forests and plains; even the skies.

Then, 66 million years ago, something terrible happened. In a geological instant, 75% of the plants and animals on Earth went extinct. And all of the land dinosaurs were wiped off the Earth forever.

What happened? What killed them off?

What could have caused that much damage in such a short amount of time?

Impactors strike during the reign of the dinosaurs (image credit: MasPix/devianart)

Impactors strike during the reign of the dinosaurs (image credit: MasPix/devianart)

The key to this mystery was found in a strange layer of ash sandwiched between layers of rock deposited 66 million years ago. This line, known as the Cretaceous-Paleogene boundary, is found across the world in the geologic record and it marks the moment when everything DIED. What’s interesting about this layer is that it’s rich in iridium, a rare element on Earth, but abundant in asteroids.

And so, geologists found the most likely culprit: an asteroid.

This evidence matched the discovery of an enormous asteroid impact basin in the Yucatán Peninsula in Mexico, centered near the town of Chicxulub. The rock debris in this area could be dated back to approximately 66 million years old, matching the worldwide layer of ash.

We now know that an asteroid at least ten kilometres across slammed off the coast of Mexico 66 million years ago, releasing 2 million times more energy than the most powerful nuclear bomb ever detonated.

The effect of this impact is mindblowing.

Chicxulub Crater

Chicxulub Crater

Millions of tonnes of rock were ejected into space on ballistic trajectories. Reheated by atmospheric re-entry, this debris superheated the air across the entire planet, catching the world’s forests on fire.

Shockwaves radiated outward from the impact site, inducing earthquakes and volcanoes along their path. Mega tsunamis thousands of meters high spread out from the impact site, pounding coastlines around the world.

Dust rained down across the planet. It filled the air, darkening the skies for decades, and preventing photosynthesis. Plants on land and in the oceans were unable to produce energy.

The planet cooled from the choking dust and aerosols, followed by years of acid rain, and then even global warming as the carbon from the blasted life filled the atmosphere.

Artists concept of asteroid impact event

Artists concept of asteroid impact event

The effects to life were devastating.

It’s no surprise the land dinosaurs didn’t make it through this impact event. In fact, it’s a bigger surprise that our ancient ancestors, hardy early mammals could endure.

And our final sobering thought is that impacts of this scale have happened many times in the past, and will happen again in the future.

It’s not a question of if, it’s a matter of when.

Additional Reading:
Scientists Come to a Conclusion: An Asteroid Killed the Dinosaurs
Giant Impact Near India Might Have Killed the Dinosaurs
Were the Dinosaurs really wiped out by an asteroid? Maybe not

About 

Fraser Cain is the publisher of Universe Today. He's also the co-host of Astronomy Cast with Dr. Pamela Gay.

Comments on this entry are closed.

  • Kevin Frushour July 18, 2013, 6:25 PM

    According to my Dinosaurs Attack cards, we did!

  • Torbjörn Larsson July 18, 2013, 7:03 PM

    And our final sobering thought is that impacts of this scale have happened many times in the past, and will happen again in the future.

    Sigh. Not this again.

    That observation alone rejects impactors as high extinction risks, because only one mass extinction has ever been conclusively shown to be triggered by an impactor. Further back larger impactors happened without any observable blips, and the risk for impactors goes down exponentially over time.

    The resolution is the same that was presented in the latest review and have AFAIK stayed since then. This specific impact happened to hit calciferous and sulfurous sediments that were scare before and are relatively scarce still.

    Impact will happen, but mass extinctions from impacts are unlikely to happen.

    Dinosaurs roamed the Earth for 135 million years. Filling every ecological niche, from the oceans, forests and plains; even the skies.

    Then, 66 million years ago, something terrible happened. In a geological instant, 75% of the plants and animals on Earth went extinct. And all of the land dinosaurs were wiped off the Earth forever.

    Ha! Try that with a 7 year old, and he will give you a major ribbing!

    Dinosaurs are still roaming the Earth, in fact their species outnumber mammals 2:1, filling nearly every niche. (Ocean dinosaurs like penguins are not obligate.)

    And as far as I know they do better than earlier dinosaurs. They never filled the oceans, other arcosaurs like ichtyosaurs, mosasaurs and pleisosaurs did that. As for the skies I suspect Cain is mistaking pterosaurs for dinosaurs (birds) as well.

    “The term “dinosaur” is restricted to just those reptiles descended from the last common ancestor of the groups Saurischia and Ornithischia (clade Dinosauria, which includes birds), and current scientific consensus is that this group excludes the pterosaurs, as well as the various groups of extinct marine reptiles, such as ichthyosaurs, plesiosaurs, and mosasaurs.[6]” [ http://en.wikipedia.org/wiki/Pterosaur ]

    I don’t mind the astronomy as much as the biology. Really, it is terrible. Not recognizing avian dinosaurs is perhaps just a 40 year old terminology change. (IIRC cladistics come to the fore in the 70’s.) But placing other arcosaurs within Dinosauria is a major no. As your nearest young dinosaur fan will tell you.

    • Fraser Cain July 18, 2013, 7:31 PM

      I’m glad to take such a ribbing from a 7-year old dinosaur fan. I think I can probably dig up a few.

    • meekGee July 18, 2013, 10:40 PM

      Torbjorn – there’s one major consideration you’re overlooking.

      Pre-civilization, the environmental change caused by the impactor had to physically kill the animals. A much smaller impact, one that merely caused 10 years worth of bad winters, would simply have caused some small effect on the populations.

      In our modern world, there’s a very fragile system in place that supports the 6 (7? 8?) Billions of us. If, for example, because of bad weather, we lose electric power on a global scale for more than a week, then there’s no water, no fuel, no food – and likely a huge amount of death. There are millions of people in every major city, that without infrastructure are simply doomed.

      And an impactor that will have global climate effects does not have to be 10 km on edge. It won’t be an “extinction”, but it could be a huge step back to civilizaiton

    • IVAN3MAN_AT_LARGE July 19, 2013, 3:09 AM

      What Killed the Dinosaurs?

      Dinosaur farts! Seriously!

      • Aqua4U July 19, 2013, 6:08 AM

        HOOT! That’s a gas!

    • Coacervate July 19, 2013, 4:59 AM

      “The term “dinosaur” is restricted to just those reptiles

      When are you going to learn that the term dinosaur is not restricted to reptiles because they are not reptiles. Shape up slacker

  • shawnirwin July 19, 2013, 12:05 AM

    If mankind gets off its behind and creates a good enough detection system, these things can be spotted long before they are anywhere near the earth . . . . and the sooner the force is applied to re-route them, the greater the re-routing effect will be. If mankind does nothing and waits, then we will join the dinosaurs . . . . and perhaps have our bones dug up some day.

  • Aqua4U July 19, 2013, 5:41 AM

    As a child I had recurring nightmares about a Tyrannosaurus Rex chasing me! (Gorgo?) I’d hide under cars then scramble out from under it at the last possible second as the dinosaur looked under and saw me. These dreams always woke me up and I’d be in a cold sweat – MA MAAA! LOL! Turns out, this is a classic childhood nightmare..Did you experience similar? Today, with the magic of CGI, Jurassic Park and other fantasy movies have brought those creatures to life for almost every child. I’ll bet there are a few out there who’ve had similar ‘bad dreams’? Thanks Holywad… I think?

    SciFi short story subject: 66 million years ago, an overpopulated and expanding space faring civilization scours the galaxy in search of suitable planets to exploit and colonize. They come across Earth and see great potential here. Observing from orbit the two crew members see a planet bursting forth with primitive lifeforms, some of large and dangerous, but most apparently benign and slow. They decide to take a closer look to perform tests for intelligence and to gather samples.

    Upon landing, the mated pair use robotics to set up a basic defensive perimeter around the landing site. The explorers immediately begin gathering plant and animal samples. They test the soils and atmosphere, water and vegetation for compatibility with their species. The work is practically non-stop and grueling in the hot and thick atmosphere and also because gravity here is higher than what they are used to. They to wear augmentation robotics which allow them to cover more ground, carry heavy loads and which provide physical and biological barriers. The enhancement suits are built for comfort but are still very cumbersome. The female is want to complain and states that the suits don’t allow them to really ‘feel the environment’ as they should were they totally immersed.

    One day after several weeks of hard work, they are lulled by the warm sun, beautiful clouds and the scent of blossoming flowers near a beautiful lake she’s chosen to explore. Suddenly, without consultation, she decides to remove her augmentation suit. Her mate tries to stop her but she laughs at him and insists that it’s safe. She explains that she’s set the guards on high alert and “It’s such a beautiful day, what could possibly go wrong?” He hesitates and she accuses him of being overly cautious to the point of being paranoid! She does not realize that some of the nearby lovely smelling flowers carry pheromones that have affected her ability to reason and helped lull her into dropping her defenses… He reluctantly agrees, also affected by the gentle chemical filled breezes.

    They eat their lunch near the beautiful lake and make love under a large tree. He’s happy and quite content and easily falls asleep in the warm sun. She looks at him and sighs.. then decides to rinse her hair and clean up a bit in the nearby lake. She dives off a rock into the clear waters and swims out several dozen yards. A large crocodilian creature living in the lake has felt her presence and moves closer for a look, assuming an easy meal. Her mate awakens suddenly when he hears her muffled scream as the creature attacks. With one swift bite it rends her body in half and the creature swallows most… He rises screaming then runs for his weapons… but it is too late.

    He returns to the landing craft filled with horror and in shock. He doesn’t bother collecting the robots, samples or tools by the lander and instead can only think of returning to the orbiting star ship. He is now alone and in great pain.. His anger builds and he begins to see this planet as a living hell, a horror that should be destroyed! He decides that is just what he’ll do… He fire up the starship’s engines and travels out past this solar systems gas giants. There he chooses his tool of destruction.. a very large cometary body. He uses the ships powerful engines to nudge the comet, to push it so that it will eventually crash into the earth. It does… he flies home, very alone and still very angry…

    • Joshua Dean July 19, 2013, 4:16 PM

      WTFDIJR?

      • William Sparrow July 19, 2013, 9:29 PM

        I’d like a bit of what Aqua4U is smoking……..

  • Matt McDowall July 19, 2013, 4:20 PM

    I thought the dinosaurs just didn’t make it to the ark in time…and that’s why they all died, they drowned ;-P

  • Glenn Fowler July 19, 2013, 6:54 PM

    There is actually quite a bit of evidence that most, if not all, of the species of dinosuar that went extinct 65 million years ago, were already extinct at the time of this impact. Massive volcanic eruptions took place over a million years or so (IIRC) either in Siberia or in India. The continued eruption I am trying to remember was in one of those two locations, as it pertains to this issue, although massive eruptions did take place in both locations at some point. I think it is the Siberian Traps (?) that are relevant to this issue as the Indian eruptions were caused by the sub-continent of India breaking apart from Africa and moving north to eventually collide with the Asian continent so again IIRC that was a long time before the extinction event regarding the dinosaurs.

    Also, there is evidence of a large climate shift and a staggering drop in water levels which occurred prior to the impact event.

    All of this is done by memory so please feel free to correct any mistakes I have on here. The point, however, is that the animals supposedly caused to go extinct by this impact, were very possibly, already extinct.

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