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Ancient impact crater may be largest ever found

Scientists in Greenland have uncovered evidence for what may be the oldest impact crater ever found. And it would be hard to find one much older, because Greenland has some of the oldest exposed rock on earth. It’s also good it happened a long time ago — this impact was huge:

(MSNBC) — Researchers think the crater was formed 3 billion years ago, making it the oldest ever found, said Danish researcher Adam Garde. The impact crater currently measures about 62 miles (100 kilometers) from one side to another. But before it eroded, it was likely more than 310 miles (500 kilometers) wide, which would make it the biggest on Earth, Garde told OurAmazingPlanet.The team has calculated it was caused by a meteorite 19 miles (30 kilometers) wide — which, if it hit Earth today, would wipe out all higher life.

How bad would a 19 mile (30 km) wide object be if it hit today?

I assumed being 500 miles away while a 19 mile-wide object made of lighter rock or solid ice struck land at a 45 degree angle with a velocity of 20 miles per second. According to the Purdue University impact simulator, the fireball would be more than 1000 times brighter than the sun. A person caught in the open, clothes and hair would ignite, skin would suffer second and third degree burns. Just glancing at the fireball as it streaked across the sky or on the horizon would cook your retinas like tiny fried eggs.

Within a few minutes red hot ejecta will begin streaking in, some of it the size of bowling balls traveling at supersonic velocity, the material will accumulate up to an average depth of thirty feet. Well before that can happen the shock wave will arrive with such force it will destroy highway overpasses, parking garages, and steel-reinforced office buildings. Most wood frame and brick structures will be reduced to rubble. The crater will be about 150 to 200 miles or more across and initially so deep it could pierce the crust and touch the mantle, before it rebounds, flows, and stabilizes at a depth of a mile or two.

If it hit water the effects would be similar, except mega tsunamis, hundreds of feet tall in many places, would lash coastlines all over the world. If such an object landed a hundred miles east of Miami, the tsunami surge along the beaches would be so enormous they could wash completely over the entire tip of the Florida peninsula from east to west.

If you play around with impact simulators for hours, like I do, and it’s a lot of fun too, you’ll see this kind of impact is way worse than the K-T, by at least an order of magnitude or two. But I don’t think it would wipe out all higher life as the article suggests, not even close. The lethal surface effects would extend to roughly one thousand miles or more. Only people in a hardened underground shelter with several meters of solid bedrock or reinforced concrete above would escape instant or lingering death inside that circle, and only those with provisions prepared to wait out a year or more of famine, drought and strange weather would live more than a month or two after that.  But this isn’t Armageddon, one of the worst sci-fi’s ever made, this is more like Larry Niven’s excellent disaster novel, Lucifer’s Hammer. Millions of people would survive, as would many animals and plants.

Wiping out most or all complex life would take something even worse, and it might look something like this.

 

Comments

  1. F says

    Most people I know do not have retinues. What can we fry instead? ;)

    That’s a fantastic discovery. Thanks for posting it.

  2. 'Tis Himself says

    If you play aorund with impact simulators for hours, like I do

    Everyone needs a hobby.

  3. zelinator says

    I read Lucifer’s Hammer in middle school. Great detailing of the aftermath of an impact.

  4. Pierce R. Butler says

    Why is the asteroid shown with veins of glowing magma on its surface even while well beyond the atmosphere?

  5. Gvlgeologist, FCD says

    Gotta say I was literally nauseated by watching that. On the other hand, that’s how we got our moon.

    I’ve never heard, though, that this has happened 5 times (I think that’s what the video said) before. Anyone know what the “evidence” they mentioned is (aside from the moon impactor)?

  6. says

    I think the ‘evidence’ is purely statistical. That clip was from a program talking about the likely impacts earth withstood right after heavy bombarbment, about 4 to 4.5 bya, after the moon formed, and how life could have survived a Vesta – Ceres sized impact on the early earth — by being underground if I recall.

    Pierce just guessing, tidal deformation as it neared earth?

  7. fredbloggs says

    Praise be to the FSM! A science post on FtB. They seem to be in short supply these days.

    Thanks for the post.

  8. sunsangnim says

    Wow. That was disturbing. But it’s another reminder that nature is completely amoral and doesn’t give a damn about us. Natural processes brought us into this world, and they can take us out.

  9. lorn says

    In many ways we are just along for the ride. Given a couple of years warning I severely doubt that we could really do much about such a large inbound rock. It might be diverted if we had a decade, two if you want a safety margin, and time to cudgel the obdurate GOP into submission after they decide it is a righteous punishment from God and we should just take the whipping like good God fearing folks. The proper authoritarian response is: “Thank-you sir, may I have another”.

    Wiping out all life is a mighty tall order. Evolution tells us that life all started with just a few microbes. So failure to get them all just means the process has to do what it has done before. With the discovery of microbes living in what was always assumed to be sterile rocks at great dept I kind of doubt any meteor impact that left the globe intact could pull it off.

    A while back I was reading about what I remember being called a gamma ray burster. Idea was that it sent out a beam of gamma rays so powerful that the cross section of the earth itself wouldn’t provide the level of shielding needed to keep anything alive. Evidently, even the roaches have limits. Good news is that death would be quick and painless.

    Odds of that seem to be slim to none. But it reinforces the idea that our existence is contingent upon our luck holding out.

  10. Pierce R. Butler says

    Stephen “DarkSyde” Andrew @ # 8: … just guessing, tidal deformation as it neared earth?

    IANAPhysicist, but I would think at the minimum you’d need more rotation of the asteroid than was shown for a true tidal effect. Without a lot of spin, some loose pieces might get rolled around – but simply falling, as a body, towards a planet seems unlikely to produce enough friction to create persistent, planetoid-wide seams of molten rock in a vacuum.

    Desire/need for maximum dramatic effect does seem sufficient to generate that result, but I’d like to think there was a little more science involved.

  11. says

    “Lucifer’s Hammer” was a clunky screed for ultra-conservative political ideology. Also crudely racist. Other than that, sure, excellent.

  12. frankkyte says

    Not really the largest impact. Only the largest crater.

    For some time there have been data on several large impacts in the early Archean (3 to 3.5 gyr). These are spherule beds, which are ejecta from basin-forming impacts. Some of these are from projectiles as large as 70 km (or larger) in diameter.

    For the most recent papers, I’d refer you to the May 3 issue of Nature (vol. 485 no. 7396) where there are two research papers and a news article on this topic (pages 44, 75, and 78).

    But a 30 km projectile is very large. Since the mass of the projectile is proportional to the cube of the radius, this has 27 times the mass (energy) of the 10 km K-T dinosaur killer. As for tsunamis, I don’t think it matters where this projectile hits. The shock will ring the Earth like a bell and the oceans will slosh around the way my bathtub does when I move quickly. Large chunks of the continental margins near the impact will probably slide off into the oceans, making even more tsunamis. The ejecta (which will carry a lot of the projectile’s energy) will super-heat the atmosphere on re-entry. Much of the atmosphere will probably be lost and lots of the ocean surface acidified and evaporated.

  13. Gvlgeologist, FCD says

    Am I the only one to think that the reason for the cracks of glowing magma was merely artistic – to make the bolide more interesting visually?

    And for anyone interested, I was wondering about the spherical shape of the bolide. According to the Wiki article about dwarf planets, the minimum size for a rocky bolide to be spherical is >600km, larger than the bolide pictured in the video. The only way for the bolide to be spherical at that size (500km) is for it to be composed of ice – unlikely considering the “magma” in the video. On the other hand, if it truly was mostly molten, then of course it would be a lot easier for it to be spherical. But then, where would an object that size and that hot come from these days?

    So I’m thinking that there’s some artistic license taken in the video.

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