How We Found the Dinosaur Doomsday Site

By Eric Betz | March 23, 2016 10:30 am

When the impact hit Mexico’s Yucatan Peninsula 66 million years ago, it wiped out most life on Earth. (Credit: NASA)

On March 22, 1991, David Kring stood at a podium at the Lunar and Planetary Science Conference in Houston and revealed the exact location of the most important impact event in the past 100 million years. The dinosaur-killing space-rock struck Mexico’s present-day Yucatan Peninsula near the town of Chicxulub.

By that time, most geologists already accepted Luis and Walter Alvarez’s once-wild theory that a 65-million-year-old, worldwide layer of iridium — a material common in asteroids, but not on Earth — implied an extinction event. But for a decade, scientists had tried and failed to find the crater.

That led many to assume an impact in the deep ocean, which might explain the absence of a bowl as big as Connecticut. Kring didn’t buy it. His gut told him the Mount Everest-sized space rock struck closer to land. The path to proving it started along the banks of the Brazos River in Texas.

Putting the Clues Together

In 1985, Jan Smit, a paleontologist at University Amsterdam, and A.J.T. Romein of the State University of Utrecht, published a summary of what was known about the Cretaceous-Tertiary event — the moment when most of Earth’s life died. Their lengthy report looked at evidence from around the world. But it was just one sentence in that 16-page paper that stood out to Kring. The paleontologists pointed to a thick layer of sandy sediment “This may be the first evidence of impact (tsunami)–triggered sediment,” Romein and Smit wrote.

That set Kring searching for an impact crater in the western hemisphere.

Scientists found the next clue in the Caribbean. Florida International University scientist Florentin Maurrasse spotted an unusually thick layer of iridium near Beloc, Haiti, that implied the dino-killing impact couldn’t be far off.

And when American television producer Robin Bates flew out for a science show about the site, he returned with a sample for Glen Izett, a geologist with the United States Geological Survey, who was next on his interview list. Inside the sediment, Izett found tiny bits of glass. These so-called tektites are only found close to impact sites.

“That told us that somewhere in the Caribbean there was a crater,” says Kring.


In the coming months, a scientific drilling operation will extract rock cores from Chicxulub’s peak ring, something never before tried. Their results could help explain the events that followed the dino-killing impact. (Credit: David Kring)

And it turned out that two geophysicists, Glen Penfield and Antonio Camargo, had already stumbled across ground zero on Mexico’s Yucatan Peninsula while looking for oil deposits. The pair wondered if the strange site was an impact crater or some kind of volcanic feature.

“They saw a circular feature, and in the oil world circular deposits mean traps,” says Kring. “When petroleum geologists see something circular, they see oil and say, ‘I want to drill that.’”

You Got It

Fortunately for Kring, the petrol hunters did exactly that. And when the pair shared the drill cores brought up from a site called Yucatan-6, it showed shocked quartz — the rocks were melted with the telltale signs of an extraterrestrial impact.

Kring got to present the smoking gun at LPSC back in 1991, but he says the find was really the work of seven North American geologists.

Chicxulub_Gravity copy

On the ground, there are few signs of a mass-extinction event in Mexico’s Yucatan Peninsula. But gravitational data reveals one of the largest craters in the inner solar system. (Credit: Virgil L. Sharpton, University of Alaska, Fairbanks)

And after he finished his talk, one man stood up in the audience. It was esteemed astrogeologist Eugene Shoemaker, the leading expert on asteroid impacts and a scientist who prepped astronauts to travel to the moon. “You got it,” Shoemaker said.

The other impact crater experts in the room that day bought the evidence as well. Later that night, a group gathered to plan the first scientific drilling operation at Chicxulub.

Tied Together

But to convince the larger geology community, Kring needed to tie the rocks recovered from Chicxulub to the rocks found in Haiti and conclusively date the impact crater. So, instead of heading to the impact site, he stayed in the lab. Over the next year, Kring was able to chemically link the sites. That scientific paper set off headlines around the world in 1992 and launched the word “Chicxulub” into the public vernacular.


The Chicxulub impact set off an airblast like a nuclear bomb that swept across much of North America, leveling forests. (Credit: David Kring)

“Finding Chicxulub was incredibly important in understanding the post-impact environmental effects,” says Kring. “Many environmental consequences are a function of distance from the impact site. So you had to know the distance from the impact site before you could evaluate the fossil record anywhere in the world.”

Chicxulub also allowed Kring and his colleagues to create a laundry list of specific environmental impacts. But scientists still don’t fully understand how global ecosystems collapsed, or exactly how they eventually recovered.

In the coming weeks, a team of scientists will begin drilling Chicxulub’s central peak ring for the first time. Discover will be on site in Mexico as the team tries to answer some of those questions.

  • Marion

    It looks like it came in at an angle. I wonder if this changed earth ‘s rotation or orbit?

    • BinaryWatcher

      Its mass was negligible relative to Earth’s (~0.0000000262% of Earth’s), so neither rotational nor orbital change is likely.

      • Randy Johnson

        Some say an earthquake relatively recently produced such effects on the Earth, measurable by space based instruments. Of course they would be really really small, but it is amazing what our top scientists are able to do lately. The gravity wave theory of Einstein finally confirmed a century after his prediction and the long accepted gravitational lensing effect on light from distant stars are other amazing discoveries related to his phenomenal mental ability.

        • BinaryWatcher

          I know. I would be inclined to agree with you, but there are a lot of factors to take into consideration, such as angle of momentum transfer and such. I have not personally sat down and tried to reconstruct the impact to that level of detail, at least as yet, so I must go with data provided by scientists who have. And they say it didn’t. I may go back and play around with it a bit, see if I come up with something different. In which case I may be publishing a paper of my own, down the road…

  • OWilson

    It would take a lot of iridium to coat the entire planet with a continuous layer, and assuming the asteroid had other major constituents, it might indicate the size of the impact object, which is not mentioned.

    I mean, how big was it?

    • Marty Johnson

      article says it was the size of Mt. Everest.

      • OWilson


        That would do it!

        • reed1v

          Doubt it. That size would have created another moon. Got to be a lot smaller.

          • Bob Juniper

            Something is fishy.

          • reed1v

            Interestingly, whatever its size, it was big enough to compress the earth’s atmosphere to basically blast away any ocean under its path; thus hitting dry land where once was an ocean.

            You can see air compression at work with the ocean mounds formed by a moving hurricane. And they only move up to 200 mph; the object in question was moving at least at terminal velocity of 78,000 mph when it hit.

            Most likely it hit before slowing to terminal velocity due to its ability to compress the gaseous atmosphere.

          • Bob Juniper

            I do that when I go off the high diving board. I have only made it to 76,000 mph but I am working
            on it.

          • BinaryWatcher

            It wasn’t the size that was pertinent here; it was the bow shock and velocity.

            Also, you may mean escape velocity, which for Earth is about 40,000km/hr or 25,000mi/hr. Terminal velocity is the speed attained by a body falling in atmosphere, at which the atmospheric drag & buoyancy compensates for gravitational acceleration, and the object stops accelerating. Terminal velocity is not a fixed number, but must be calculated for each object, depending on its shape.

            The estimated velocity of the Chixulub impactor was of order 20km/s or 12.4mi/s, which is just shy of 45,000 mph. This is substantiated by attempts to model the impact at the Los Alamos National Labs.

          • reed1v

            No, I was referring to the terminal velocity, or the speed at the point of “impact”. Was not aware of LANL’ s work. In any event, 45k mph or 73k kph +/- still would have likely parted the oceans before point of impact. Did LANL also model the atmospheric compression in its analysis?

          • BinaryWatcher

            “Terminal velocity” as a term is not applicable here. Impact velocity is the term you’re looking for.

            But yes, the bow shock largely pushed aside much of the atmosphere and most of the water — not that it made a lot of difference. The megatsunami produced was estimated at several miles high, and did not decrease a lot several hundred miles inland. Most of the impactor analyses model the bow shock, but they are generally not interested in the degree of compression in the shock wave, only the effects.

          • reed1v

            Impact velocity probably was close to terminal velocity. Question is whether terminal velocity as normally defined even applies to huge falling bodies that essentially push away most of the atmosphere?

          • BinaryWatcher

            No. Entry/impact velocities are so high for such impactors that often there isn’t even time for the object to react to the fact that they have even encountered atmosphere before the impact occurs. And impact velocity is far far greater than typical terminal velocities. Objects falling from height in atmosphere typically have terminal velocities ranging from 50-75 m/s. The Chixulub impactor had an impact velocity over 11 thousand m/s.

            This is why I said “terminal velocity” does not apply here. It is defined in such a way that it CANNOT apply. The term you want is impact velocity.

          • reed1v

            Thanks. That is what i assumed,but on other sites, kept getting folks saying nothing can exceed terminal velocity(i.e. everything slows down to or speeds up to terminal velocity). Did not make intuitive sense when dealing with massive bodies. Which raises another question:

            As you pointed out previously, this was a relatively small object relative to Earth; so what would be the minimum size to affect the Earth’s orbital motions?

          • BinaryWatcher

            Whoever was on those other sites *bites tongue* Right. Moving on.

            Just so you know, this is not intended to blow my own horn, but to inform you where I’m coming from: my graduate work was in astronomy, and I also studied physics and geology in undergrad school, among other sciences (I’m considered a polymath). I was on an impact effects mitigation working group for a couple years and have dinked around with the physics of impactors for years. That said, that was not my principal focus, so while I’m probably “more expert” than the average layperson, I’m less expert than the people who’ve made it their principal professional focus.

            Now, with respect to affecting Earth’s motions, I don’t have a good answer offhand. This is because it depends on many factors, including velocity, angle of impact, angle of impact relative to rotational motion/orbital motion, density of object (which is determined by composition), et cetera, ad infinitum, ad nauseam. I would have expected the Chixulub impactor TO HAVE AFFECTED these things, but the studies I’m seeing indicated it didn’t.

            I’ve not sat down and tried to calculate all of that, and right now I don’t have time to do so — I’m prepping to be out of town all next week, consulting for a governmental confab, AND this is a holiday weekend with family obligations too, so a bit hectic. (Got my speech prepared, half packed, laundry done… you get the idea.) So as much as I’d like to give you one, I don’t have an answer to your question right at the moment, and no chance to work one out in the near future. Sorry about that.

            That said, Google (or whatever your favorite search engine) is your friend in this regard. Start playing around with combinations of keywords, or even phrases, such as “minimum size impactor to affect Earth orbit” or the like, and see what you come up with. Try to screen the results to ensure you get legitimate science, and you’d be surprised what you can learn. I’m a science fiction writer these days (after having spent a career in the space program), and that’s always one of my starting research approaches.

          • BinaryWatcher

            General consensus is that the impactor was on order 6 mi/10km in diameter, and was probably either a carbonaceous chondrite or a comet, both of which are relatively low in density. If we assume a chondrite, then the density is about 3g/cc. Scaling up and determining the mass of a rough sphere of diameter 10km, we get 1.57×10^15kg. Earth’s mass is about 6×10^24kg, so the mass of the impactor is about 0.0000000262% of Earth’s; negligible in comparison. The Theia impact hypothesis requires a Mars-sized body, some 6×10^23kg, or about 10% of Earth’s mass.

          • reed1v

            Otoh, could have been solid debris from who knows where. Even solid iron would have vaporized on contact. Hope they do some deep mantle bores in the area(wishful thinking). Plus little moons would require much less than 10% of Earth’s mass. Perhaps this was an early proto-moon that finally plunged to earth.

          • BinaryWatcher

            It was more or less solid debris, yes — chondrites and comets are both solid objects. But the impact energy is easy to calculate based on the size of the crater; ditto the rough diameter of the impactor. Once you have those things, then you can determine the mass and density of the object. As I said, general scientific opinion is that it was some 10-12 kilometers across, and either a carbonaceous chondrite or a comet.

            As for “deep mantle bores,” there is no such thing currently. The deepest borehole ever drilled was about 12km deep, in Siberia — into continental crust. Continental crust is 30-50km deep, depending on whether or not there are mountains (which increase the thickness). So we are not even halfway to REACHING the mantle, let alone being able to drill a deep mantle bore.

            The Chixulub impact occurred some 66 million years ago. Earth (and the rest of the Solar System) formed some 4.5 BILLION years ago. So Chixulub is less than 1.5% as old as Earth. Any protosatellite that was in an orbit unstable enough to drop out of that orbit would have done so long before, in the first few hundred million years after the system formed. No, almost certainly this was an Earth-crosser asteroid.

            Astronomers are currently attempting to ascertain the chemistry of the impactor, as well as its probable incoming trajectory (which latter can be determined by the distribution of ejecta). This is being done in order that they can try to categorize the impactor as belonging to one of the Earth-crossing asteroid groups.

          • reed1v

            Yes, that is why i noted wishful thinking about mantel exploration. While your analysis is spot on, still, its not too wild a speculation that other bodies orbiting Earth might have been perturbed by errant visitors, either from within the solar system or from beyond.

          • BinaryWatcher

            Yes, it’s possible — but not probable. Far more probable is an Earth-crossing asteroid. Why? The estimated velocity at impact was nearly twice Earth’s escape velocity. An orbiting body is VERY unlikely to more than double its speed by the time it impacts. If it is far enough out for that kind of velocity to build up, then chances are it was not in orbit to begin with.

          • reed1v

            Good point. Was rather wishing for a two moons-one earth scenario. Which raises the question what would be the maximum distance a body could be in a stable orbit around Earth?

          • OWilson

            Maybe the “Everest size” was just a relative term to describe something around 6 miles high that average folk could picture.

            I wouldn’t take it literally :)

          • reed1v

            Somehow that would create an image in my mind of an inverted ice cream cone hitting the earth.

    • BinaryWatcher

      The majority of isotopes of iridium are radioactive, so it is relatively easy, between radiation detection and chemical detection, to determine the presence and quantity of iridium in the thin stratum of depositional material at the K-Pg boundary (used to be called the K-T boundary, but they changed “Tertiary” to “Paleogene” a few years back).

      • OWilson

        When Alvarez discovered the layer of iridium a few years back, it was because the layer was quite visible, quite substantial and continuous. It was even obvious to we viewers in a documentary produced at the time.

        No need for chemical or radioactive instruments.

        That’s a lot of iridium, if it is truly world wide.

        Just sayin’

        • BinaryWatcher

          Yes, because it was a layer of SEDIMENT from the EJECTA, that INCLUDED the iridium. It wasn’t all iridium.

          • OWilson

            That’s still a lot of iridium.

            (And you don’t have to shout!) :)

          • BinaryWatcher

            Relatively speaking, yes it was. That’s how we know that the layer was produced by an impact, because iridium is VERY rare on Earth.

            (And I wasn’t shouting. Read the whole comment.)

            And on that note, I have serious work to be done, guys. So I’m afraid I’ll have to bow out of this conversation. It’s been fun, and I hope I’ve helped explain a few things for folks.

        • stargene

          A rough wrinkle in the ointment… there is a crude ratio, giving crater diameter/impactor diameter. I can’t find an explicit site giving this, but the ratio seems to range from about 10 to about 30. The
          ~30 value comes from the example of the Arizona Meteor Crater: Crater about 1 mile wide and the impactor estimated to be 164 feet wide.

  • Alex

    Monument in the center of Chicxulub Puerto.

  • Christopher Coulon

    Can we please rethink the “extinction of the dinosaurs” feature? There are almost twice as many species of dinosaur alive today as mammals; the mammals are larger, but not more numerous. All the animal groups were brought to their knees, but the dinosaurs were not rendered extinct.

    • Austin Reed

      Dinosaurs, as we know them, are extinct. Obviously they evolved into today’s modern birds and lizards, but that does not make them any less extinct. It’s like saying australopithecus isn’t extinct. They are all gone. That’s what extinct means

      • Christopher Coulon

        Dinosaurs evolved into lizards? That’s like saying mammals evolved into fish. When the extinction event happened, only small flying or nocturnal forms of dinosaurs and mammals survived and began their evolution into their current forms. Mammals evolved from small insectivorous creatures and birds evolved from small flying dinosaurs; none of the intermediate forms survive to the present.

        • reed1v

          Don’t forget the horseshoe crab. Been around almost half billion years. Was here before the dinosaurs and will probably be here long after humans are extinct.

          • Christopher Coulon

            Xiphosuridae, related to scorpions and spiders, they may be the last vestige of the trilobites, most of whom died off in the Permian extinction event.

          • reed1v

            Side issue: The upstate New York shale formations in the Finger Lakes region contain huge collections of trilobites. Split any shale and you will most likely find trilobite fossils. Small, but a nice link back in time.

        • Austin Reed

          Now you are nit-picking. Yes, dinosaurs evolved into modern lizards. The big ones died out, and the small ones were better suited to their new environment. Modern lizards are the decendants of the reptiles that lived during the Cretaceous. We refer to that group of reptiles loosely as dinosaurs. It’s not a technical term. That’s evolution. Quit being obtuse

          • Christopher Coulon

            Sorry Austin, nothing personal, but you need to revisit your phylogeny.

          • Austin Reed

            Fair enough. The consensus up-votes seems to favor you. I am technically incorrect. However, generally speaking, it is useful to say that the dinosaurs went extinct. Most of them did. Next time, I will check up on the proper terminology before I argue

          • Christopher Coulon

            Austin, I commend you on your humility! Few are those who can admit to be mistaken. Of course nothing is certain, but the fossil record is getting more complete, and Archaeopteryx, at 150 million years ago (late Jurassic) is no longer the earliest feathered dinosaur; it appears that there were flying dinosaurs at that time. Pterosaurs were reptiles, not dinosaurs, and they lacked feathers. It’s always best to see the truth in what another writes; our strength comes from unity, not division. 😉

          • Randy Johnson

            Exactitude has great value and the perversion of language by those who scheme to deceive, like calling a democratic socialist a socialist or a communist. That deception does great disservice to our nation and makes for a bunch of fooled fools.

          • Randy Johnson

            Ontogeny recapitulates phylogeny.

          • Lorie Franceschi

            Actually reptiles are from the Carboniferous period around 310-320 Million years ago (Laurin, M.; Reisz, R. R. (1995). “A reevaluation of early amniote phylogeny” (PDF). Zoological Journal of the Linnean Society 113 (2): 165–223). Dinosaurs evolved from reptiles, not the other way around.

          • Sharon McKenzie

            No, Austin, dinosaurs did NOT evolve into modern lizards and aren’t related to them at all! Dinosaurs are no more related to modern lizards than we humans are, probably less so. We need to drop this whole notion of dinosaurs as slow-moving, ectothermic, scaly reptiles, because every recent paleontology discovery points in the opposite direction. Birds, yes. Lizards? No. Lizards and other reptiles came BEFORE the dinosaurs, so it would make absolutely no sense, evolution-wise, for the more-advanced dinosaurs of the Late Cretaceous to “de-evolve” into simpler organisms. Everything we know about the outer coverings and even the internal structures and skeletal development of dinosaurs is very unlike any living reptile.

        • dogfightwithdogma

          There were no “small flying” dinosaurs. There were no flying dinosaurs of any type, shape or size. All dinosaurs were land animals. The flying reptiles of that time were pterosaurs, none of which were part of the group we call dinosaurs.

          • Christopher Coulon

            It’s always best to be informed before writing an opinion, but whatever; I’m not going to quibble.

          • dogfightwithdogma

            I agree that one should be informed before expressing an opinion. I was not, however, expressing an opinion. There were no flying dinosaurs is a fact, not an opinion. So we are not quibbling over opinions, which are or can be subject to quibbling. You stated as a factual claim that there were “small flying” dinosaurs. This is factually incorrect.

          • Randy Johnson

            Did pterosaurs not evolve from dinosaurs? Sheesh!

    • Randy Johnson

      I think dinosaurs and mammals evolved from common ancestors and were both living at the time of the extinction event. However, mammals did not evolve from dinosaurs. You seem to be mixing up the limbs of the tree of life. We have been warned very early to not eat from that tree, so I hope you don’t let our Congress take away our right to know if GMOs are in the food we buy at our grocery suppliers. Republican majority House reps passed a bill to do that and it was defeated in the Senate by only one vote. My two senators’ votes cancelled each other out. Phew!!

  • Small_Businessman

    I just want to say this is one or the more interesting discussions on this board in a long time. Lots of knowledgeable people, no faux science and (almost) no quibbling over words. A very refreshing change to some I’ve seen lately, especially on other boards. Everyone here shoud be proud of how they can share information in a mature way.

    • Randy Johnson

      Too those of us interested in accuracy quibbling over words seems necessary. Sorry if you don’t like it.

      • Small_Businessman

        Quibbling over words has nothing to do with accuracy – except to an idiot or a troll. Which are you?

        • Dewey Cheatem

          So now the person who said how proud they were of such maturity is all the sudden calling people an idiot and troll…sounds like you are the one who shouldn’t even log onto the Internet at all.
          Go back to playing Candy Crush with your little teenie friends.. your lack of education is abundently obvious.

          • Small_Businessman

            Yes, I have little patience for either trolls or idiots. And I call them like I see them.
            And I’m much older than you think. Old enough that I really don’t give a rat’s a$$ what idiots and trolls like you think. Your own words say everything.

  • Tarun Malik

    It has happened before. It will happen again. Only question is when ? A month later or 2 million years later. Does it not make sense to unite together and keep solutions ready ?

    • Randy Johnson

      DUH; Yep, I think so, but you can’t depend on the strife stirring GOPers to ever get it done. All they are interested in is feathering their own and their masters’ nests at the expense of the rest of the planet’s species and ignoring scientists not bought by them.

      • BinaryWatcher

        Is it really necessary to bring politics into everything, guys?

        • Small_Businessman

          Now we know. Randy is both a troll and an idiot.

  • Randy Johnson

    Due to anthropogenic ?sp. climate heating acceleration, most of us are probably going to miss the next fire and brimstone event.

  • Michael Davias

    Scientists have correctly identified Chicxulub as the most important impact in the last 100 Million years. Scientist have also correctly identified The Chesapeake Bay impact as the most important one in the last 50 Million years. But the most important impact in the last Million years – the one that created the Australasian Tektite Strewn Field ~785,000 years ago (i.e., yesterday)- has yet to be identified. Not for lack of trying: the impact community experts have been combing IndoChina for the past 60 years. It must be enormous, given the fact that these tektites are not little dots of glass – there are an estimated 60 Billion tons of them, and you can buy handfuls of them in eBay for $10 because they are so common across 1/4 of the globe. Scientists are searching in the midst of the tektite strewn field for the crater, but it is probably at an antipodal location given the forensics of the suborbital flight times indicated in the distribution of the strewn field and the evidence that most of the tektites re-entered the atmosphere at close to Earth escape velocity (10-11 km/sec). The chemistry of the Australasian tektites suggest to me that they were derived from an impact into a deep ice sheet, like the one covering North America 800,000 years ago. They won’t listen to my team, as they are the “experts” and know it all (and we did try once again at last week’s LPSC) . No matter, every decade they spend in IndoChina gives us more time to gather the necessary evidence from our suspect impact structure and ejecta sheet.

    • OWilson

      Maybe you could trick them.

      Say you want to explore the Hawaii, Rio, or Costa Rica anomolies,
      (in February) then divert them to the site of actual interest :)

      Good luck!

  • stargene

    I just want to elaborate on a couple of kinds of evidence for confirming
    an asteroid hit, rather than an enormous volcanic eruption, and locating
    its crater. First, the shocked quartz grains were not melted, but, more tellingly, they were multiply shocked, sometimes having as many as three differently paralleled groups of shock planes. This was the smoking gun, because no volcanic explosions can ever be powerful enough, over a small enough time interval, to create multiply shocked quartz grains.

    Second, fairly early on, some researchers realized that the global distribution of these same grains and other signature particles was going to have a gradient in size… the larger ones will have fallen out close to
    the impact point and smaller ones will have fallen out, on average, at
    greater and greater distances, according to their size. This was indeed
    what the impact grains showed, zeroing in on the Yucatan peninsula.
    Together, these two separate lines of data formed a beautiful “Gotcha”
    on Chicxulub!

  • OWilson

    If you look at the other solid objects in the solar system, from Pluto to Mercury, and including even relatively small asteroids, the are all pock marked with countless impact craters from the early solar system. There are craters within craters.

    While most of the flying objects have been “vacuumed up” by the major planets, there are still more than enough out there that will probably completely obliterate the current earth’s surface, over time.

    Our 100 year lifetime makes us statistically safe from these events.

    Our old history teacher used to say, with regard to England, “There’s probably not a spot anywhere where a battle has not been fought, or at least someone run through with a spear”.

  • Ryan Choate

    Funny how no one considered the possibility of not one but multiple asteroid impact. If one big asteroid came through why not whole bunch of other smaller ones that impacted the Planet too. And contribution to that could triggered a massive chain reaction that could have started earthquakes and volcanic eruptions too, is that possible.


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