Could an Asteroid have Wiped Out the Dinos?

Posted by Ethan on May 7, 2009
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I recently got this comment of incredulity on my article about what wiped out the dinosaurs?

I´m sorry. But i don´t believe this. In my opinion they were wiped out by a climatic changing.

And I think it’s worth — with the help of a little math and physics — looking at what this asteroid impact might have done.

First off, we need to know how massive this asteroid was. This asteroid was about 10 to 12 km in diameter, which is large, but less than 0.2% the diameter of the Earth. It’s pretty unremarkable, and makes it a pretty typical minor asteroid. For comparison, this makes it about half the size of the known asteroid Gaspra, shown below.

What we’re going to do is figure out the mass of our asteroid, calculate how much energy it hit the Earth with, and see whether that would be enough to have an appreciable effect on the entire planet.

Mass first. For a sphere that’s 10 km in diameter, let’s assume it’s got the same density as typical rocks on the Earth’s surface; about 3 grams per cubic centimeter. I get that this asteroid was about 1.6 x 10^15 kg in mass. That’s a big number, but it’s significantly smaller and lower in mass than, say, Mount Everest.

The thing that makes this asteroid so vicious, though, is that it had so much kinetic energy when it hit the planet! There are many ways to figure out just how much, but one of the easiest involves a neat physics trick. This asteroid started somewhere out around Jupiter, and fell in towards the Sun. It was only coincidence that it ran into the Earth (that’s what we get for being in the way).

The great trick here is realizing that the asteroid gets pulled in by the Sun, and that — by the law of conservation of energy — the gravitational potential energy that it loses is going to equal the kinetic energy of the rock when it strikes us!

i-fb4d0e0799215767446514b273a144c7-d7456002a3762eca3554a9cc05f19d86.png
So, m_1 is the mass of the asteroid and m_2 is the mass of the Sun. The energy of the rock is then going to be the difference between that equation with R as the distance from the Sun to Jupiter and that same equation with R as the distance from the Sun to the Earth. When I put those numbers in (along with G), I get that the total kinetic energy of the asteroid just before it impacts Earth is just slightly more than 10^27 Joules!

Joules, Ethan? Nobody uses Joules. When we talk about large amounts of energy, we use Megatons!

The largest nuclear weapon ever detonated on this planet was the Tsar Bomba, with a yield of around 50 Megatons. (The original Soviet footage of the detonation is shown above.) What is 50 Megatons in Joules? A paltry 2 x 10^17 Joules.

This means that this “minor” asteroid, impacting with the Earth, released as much energy as 5 billion of the most powerful nuclear bombs ever built going off all at once.

And that is why it’s so hard to believe that — with this much energy released in an impact — this wouldn’t have directly caused a mass extinction. The conservation of energy doesn’t lie.

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Comments

  1. #1 Ty
    May 7, 2009

    Kinetic energy, she is a harsh mistress.

  2. #2 Jesse Dill
    May 7, 2009

    Nice post! But I feel that megatons and joules aren’t truly intuitive units of measurement. How many hostess cupcakes’ worth was it?

  3. #3 Brando
    May 7, 2009

    Some crazy facts on Tsar Bomba:

    1. Yield reduced (with a lead tamper) from a 100Mt design.
    2. Air dropped weapon (largest US tests weren’t weaponized)
    3. Detonated at about 4000m AGL
    4. Shockwave propagation amplified to affect towns 70km away

    And as you said, small peanuts compared to the Chicxalub impactor

  4. #4 Andrew
    May 7, 2009

    The usual estimate quoted (from Covey et al. 1994) is ~10^8 megatonnes, or ~5×10^23 joules, so you’re about three orders of magnitude high; but it’s still a very impressive amount of energy.

    (The Tsar Bomba wasn’t an especially practical weapon, even though it could have delivered 100 megatonnes, not just the 50 it was tested at, since it was intentionally downrated to keep the test reasonably clean.)

  5. #5 D. C. Sessions
    May 7, 2009

    It makes quite a difference whether the impact was on land or water, too. Ocean bottom is much thinner, and the result is that you get a lot more magmatic release. A land strike will put up somewhat more dust, a water strike more water vapor.

    The thermonuclear release from all of that hydrogen fusing will not even register.

    No matter where it hits, anything within line of sight is instant flash vapor: the radiation from it hitting the top of the atmosphere will immediately start any organics (forests, for instance) burning almost explosively. Again, the energy release is trivial but the smoke and carbon dioxide is not.

    Lots more — if you never read J. E. Enever’s “Giant Meteor Impact” (1966) it’s worth while. As far as I know, it was the first published quantitative analysis of this sort.

  6. #6 g
    May 7, 2009

    How’s this for intuitive units: the entire sky turns into an oven set on “broil” for several hours.

    Survival in the first hours of the Cenozoic. Robertson, D. S., McKenna, M.C., Toon, O. B., Hope, S. and Lillegraven, J. A. 2004. GSA Bulletin 116:760-768

  7. #7 Mu
    May 7, 2009

    I thought that the “broil” thing was always a bit troublesome. Why does this kill all dinosaurs, but not mamals, or reptiles like crocodilians etc.? Why do all aquatic dinosaurs die too, but not sharks and turtles? If you have a total loss of habitat, why is it still selective by family, not e. g. by size? Easy to see that all large animals die, if not immediately but soon since the diminished food supply can’t support them. If there’s enough food for the sharks to survive, why not the aquatic dinosaurs?
    Somehow explaining a selective extinction by a single cause seems trickier than a total.

  8. #8 Glen Davidson
    May 7, 2009

    That the asteroid likely kicked up a lot of sulfur from the rocks it hit, and ignited a large number of fires as well, is thought to be likely contributors to a mass extinction.

    That something so small in comparison to earth could kill off so much of life does seem, at first blush, a bit surprising. What’s important is that it doesn’t take much mass of sulfur dioxide, NOx, and soot from fires to severely reduce sunlight for a few years. Which is enough time to kill off the larger animals, and even many of the smaller ones.

    Glen D
    http://tinyurl.com/6mb592

  9. #9 Badger3k
    May 7, 2009

    There’s also the oxygen hypothesis – that oxygen levels were higher, giving the dinosaurs an advantage. If this is something real, then an asteroid that disrupted the atmosphere, maybe reducing oxygen, would have given those creatures who were better in lower oxygen, such as mammals, a leg up. Not sure about the oceans, though, but wouldn’t an impact have an effect on them, beyond the shock – chemical changes maybe? Just a few stray thoughts while waiting at work – I am not qualified to assess the likeliehood of either. But it is an interesting topic.

  10. #10 Oscar Zoalaster
    May 7, 2009

    Would the amount of energy at impact be different if the asteroid had rounded the sun and was headed back out towards the orbit of Jupiter? I would think that as it got further from the sun the speed of the rock would slow down until it starts falling back towards the sun and it starts speeding up again. Or would the difference be too small to matter except in the details?

  11. #11 D. C. Sessions
    May 7, 2009

    Would the amount of energy at impact be different if the asteroid had rounded the sun and was headed back out towards the orbit of Jupiter?

    Nope. The calculation is purely from conservation of energy: it was there, it is here, therefore it has some amount of additional kinetic energy. Actually, the analysis fails a bit due to the rock starting at a lower orbital velocity and having to pick up relative to Earth’s greater one. However, the difference is only a modest scalar (about one-third) which is pretty much in the noise for these orders of magnitude.

    An alternative, by the way, would be a starting point farther out. Comets really buzz through the inner Solar system, and it’s that kilometers-per-second thing that packs the big punch.

  12. #12 Brian
    May 7, 2009

    Ethan, you make a strong case for why the impact would have been very disruptive to life on Earth. It certainly played an important role in the extinction of the dinosaurs, but some evidence suggests the extinction was more gradual than we have previously been led to believe. Dinosaur numbers were on the decline for hundreds of thousands of years prior to the impact. Perhaps this was due to a climatic shift. The impact event probably just accelerated these events that were already set in motion.

  13. #13 Lassi Hippeläinen
    May 8, 2009

    If you look for a single cause, you’ve been watching TV too much. More likely there were several factors at work (e.g. the Deccan Traps) and the meteor impact just expedited extinctions that would have happened anyway. If things had returned to normal after the impact, the dinosaurs would have rebounded.

  14. #14 llewelly
    May 9, 2009

    Why does this kill all dinosaurs, but not mammals, or reptiles like crocodilians etc.?

    The K-T didn’t kill all dinosaurs. A substantial (but minority) portion of therapods (those being avians) survived.
    And it did kill large portions of mammals, reptiles, and crocodilians. But the K-T event did kill all Ammonites.
    Other than that – I had thought scientists still viewed questions like ‘why did the K-T event kill animal group X and not Y’ as very hard questions to answer.

  15. #15 Jonathan
    May 16, 2009

    Clearly, an intelligent species of dinosaurs set off a large nuclear device that annihilated all the dinosaurs. Why would they build such a device? So as not to fall behind the doomsday gap.

  16. #16 Anonymous
    July 5, 2009

    wooooooooooooooooooooooooooooooooooooooooooooooooooool

  17. #17 gpalonen
    February 9, 2011

    Is it possible that the continental plates divided after an impact of great magnitude caused by an asteroid. Life on the surface of the earth would suffer extinction leaving it’s evidence behind.

  18. #18 Paul Felix Schott
    January 15, 2013

    2013 Dec 24-26

    ALL THAT EVER LIVED ON EARTH WILL SOON HAVE THEIR EYES TO THE HEAVENS

    Do a little History on this one.

    ALL Should Look Up “2012 DA14″.

    This could take out one of more satellites and the junk and debris from the hit could end up taking out many more satellites very soon after that. All the satellite collision probability will go way up if even one is hit. The velocity that the parts would go to would make them missiles that would start targeting a chain reaction this would not be good.

    Most all will be watching this one and pray it goes by us without a hit. Every Scientist alive will be watching this event. Many will be in Florida for a very special viewing of the once in a Lifetime Event. Professors, Scientist, World Leaders, Ham Radio Operators and Every Astronomer will have its eyes on This Event, along with almost every TV set on Earth.

    “2012 DA14″ goes by Earth twice a year and there is no way anyone for sure, can tell how close the second pass will be till it passes by the Moon and Earth and the GRAVITATIONAL FORCE effect that it will have on this Asteroid.

    They may come close but this one is already coming very close to begin with. Too close this time or on its second or 3rd pass? Ad a Meteor Shower like the 13 and 14 of December of 2012, it might go through or bump into one of them? Or all the other more then 20,00 pieces of orbital debris like Spent Rocket Boosters left in space that can no longer be moved by a control center on Earth. Or add a Solar Flare. Or a Comet ISON or its tail debris of millions of rocks of all sizes.

    If a big enough one were to slam into the moon in the night sky you would think the sun was coming up early only it would be 5 to 7 times as bright. From The Sun’s Rays Reflection on all the Debris Field.

    2012 XM16, 2012 XM55, 2012 XP55, THERE ARE OVER 25 found just in the year 2012 that are part of the Near Earth Object Program that will come close to Earth from now till 2012 DA14 comes, Feb 14 – 16, 2013.

    You do not want to know how many are on the “PLANETARY DEFENSE” list.
    The PLANETARY DEFENSE is not to protect Earth from men from Mars.
    It is for all mankind with most all Nation in on it to stop if can most all collision with EARTH from a ASTEROID IMPACT. It is if you will a AVOIDANCE SHIELD. “N.E.O.S. Near Earth Object Shield”.

    If only one were to hit or IMPACT EARTH on land get ready for a winter you will never forget. The winter from 1883 -1884 KRAKATOA you will think was a little pebble, and now the stone comes.

    A Shock Wave was felt in England from a Event about 7:15 to 7:20 A.M. Siberia time in the morning in June of the year 1908 high in the sky above the Forest in the remote wilderness of Tunguska Siberia heard an explosion that laid flat more than 800 square miles of the forest with all the trees pointing away from the center of the blast with most all the trees laying on their side. Some trees that were right below the blast were still there looking like telephone poles with no bark or branches left on them. This Asteroid did not even hit the Ground and this is known by most as the TUNGUSKA EVENT. For all that lived there it was WORMWOOD Rev 8:11 the wood became full of worms and the rivers water no longer sweet and undrinkable.

    If a Meteor Shower is big enough you might think all the stars are falling from Heaven.

    About one every 100 years makes it into the Earth’s Atmosphere big enough for all to take note. Some make it to the surface the signs are all over the Planet and moon from the ones that have.

    If you need a visual sign of a collided impact with a planet look to

    “SHOEMAKER – LEVY 9″ July 1994.

    You Need More Look up “PROJECT WORMWOOD” Revelations 8: 10 – 11 based on the “TUNGUSKA EVENT” 1908

    Better to be safe then sorry.

    GET READY

    Read your Bible
    While you still can,
    and May our Lord GOD Bless all that do so.
    John 14 : 6
    Luke 13 : 27
    Matthew 7 : 20 – 27

    Matthew 12:39

    Matthew 24:3 – 14

    The Lord’s Little Helper.
    Paul Felix Schott.

    December 24 – 26, 2013 the Heavens above COMET “C/2012 S1″, “ISON”.

    ALL ON EARTH WILL SEE THIS NO MATTER WHERE YOU ARE. the night side of earth will become day and and day will be blinding bright.

    Shortly there after you will think the stars are falling from the Heavens, from ISON long tail if it dose not eat Mars first and makes it around the SUN.

    P.S.
    Help others in are Lord’s name Jesus Christ help bring all to know him while you still can.

  19. #19 Sean T
    January 16, 2013

    @Paul Felix Schott,

    A little math could help you sleep a bit better. Short story: it’s VERY unlikely that this astroid would hit a satellite. (As for it’s hitting the earth, that probability is zero).

    Details:

    Consider the volume of space in which the astroid might collide with a satellite. This volume is equal to the difference between the spherical volume with a radius equal to the distance from earth’s center of the highest sattelites and that of a sphere whose radius is equal to the closest approach of the astroid. For a sphere V = 4/3 * pi * r^3. The radius of geosynchronous sattelites is 42164 km. For the astroid’s closest approach, the radius is 34100 km. Therefore, this volume would equal 1.48 E14 km^3. Now, the astroid will occupy an approximately cylidrical volume of space during its transit with the radius of the cylinder equal to the astroid’s radius and the length equal to the path length of the astroid’s orbit inside the volume given above. This length is maximally (from geometric considerations) 49598 km, and the radius of the astroid is 0.0225 km (22.5 m). Therefore, the volume occupied by the astroid during its transit of the volume in question is 78.9 km^3.

    To collide with a satellite, the volume occupied by one of the satellites in this region must coincide with the volume occupied by the astroid. There are several thousand satellites currently in orbit, but the number that would be potential targets of the astroid would be a small fraction of that (most are in low earth orbit). Even so, let’s assume 5000 potential target satellites, and that each has a radius of 1km (obviously most are much smaller, but I’m being conservative here.) Given these assumptions, the total volume of all target satellites is 20944 km^3. Dividing the total volume by this value gives 7.06 trillion. Thus, the probability of any target satellite being within a given cubic km of space inside this volume is 1 in 7.06 billion. Since the astroid passes through 78.9 km^3 of volume division by this factor gives an estimate of the probability of collision, which is 1 in 89.5 million.

    Note that the actual probability is likely MUCH smaller than this. This is actually the probability that the astroid will occupy the same volume as one of the satellites. It is not the probability that the astroid will occupy the same volume as a satellite SIMULTANEOUSLY. Therefore, since both satellites and astroid will be moving, the real probability is much more remote, and I, for one, will not be losing any sleep over it.

  20. #20 Sean T
    January 16, 2013

    Part of the problem is that most people have no concept of just how big a volume all these satellites are in. The picture you seem to have in mind is that of a crowded highway, in which one collision would lead to chain reactions of collisions. In all likelihood, the collision of an astroid with a satellite would only cause damage to that satellite.

    Consider that, on average, the distance from a given satellite to the next closest one is approximately 3900 km. It’s hard to see how an impact by an astroid would lead to any kind of chain reaction.

  21. #21 Wow
    January 16, 2013

    “ALL THAT EVER LIVED ON EARTH WILL SOON HAVE THEIR EYES TO THE HEAVENS”

    Well, apart from the dead.

    Or the blind.

    Or those without eyes.