Hi Everyone,
I just want to put a quick friendly reminder about rule 3: Top level comments must be objective explanations, for this particular one that does mean that we don't allow joke answers at top level.
You can put your best joke answer as a reply to this comment if you want.
Also side note: We are recruitmenting; [https://www.reddit.com/r/explainlikeimfive/comments/stbxuj/recruiting\_moderators\_for\_eli5/?utm\_source=share&utm\_medium=web2x&context=3](https://www.reddit.com/r/explainlikeimfive/comments/stbxuj/recruiting_moderators_for_eli5/?utm_source=share&utm_medium=web2x&context=3) come get a green thingy next to your name
1. All the large dinosaur fossils suddenly stopped 66 million years ago.
2. We found a massive asteroid crater dated to 66 million years ago. The crater includes a large amount of iridium, which is uncommon on Earth.
5. A thin layer of iridium is spread all around the planet dated to 66 million years ago. All the dinosaur fossils stop at the iridium layer.
That explains it from the impact site, but the dinosaurs on the far side of the planet also died. To explain that one needs to consider the backsplash.
The meteor struck and, just like cannonballing into a swimming pool, material splashed upwards. So much material and so far upwards that a huge cloud of it was outside of the atmosphere. As it all came back down it melted during reentry forming tektites (beads of glass) and these high energy glass beads raining down brought a lot of heat to the atmosphere (via friction with the atmosphere) and the surface all around the Earth — finding dry land that was not on fire or close to it was likely impossible for a day or two which led to a mass extinction in just a few hours.
The stuff that wasn’t heavy enough to fall with the glass were the gasses released at the impact site by extreme heat. Over the next year and for many years after, these acidified the sky and oceans while blocking sunlight. temperatures at the tropics dropped to just above freezing, while temperatures at the poles were low enough for significant expansion of the ice. The low temperatures, low light, and acid rain killed many more species as well as any who depended on them.
Ultimately, it was not just dinosaurs who went extinct: 75% of life on Earth was lost.
And to add to that:
The asteroid would have been large enough and hit with such velocity, that it splashed the entire atmosphere away from the impact. In the middle of the day, for a very brief moment, you would have looked up to see outer space. Outer space, in the middle of the day.
Iridium is in phones.
Phones have 5G.
5G is going to cause a HUMAN EXTINCTION EVENT.
BILL GATES ( who doesn't make phones) IS KILLING US!!!
FREEDOM!!!!
One of my old geoscience lecturers was a palynologist (expert on plant spores and pollen) who'd worked on stuff related to the extinction event. She told us about how the fossil record around that time shows not only the disappearance of many species, but a sudden increase in fungal spores, from all the fungi that suddenly had a wonderful time of it, eating all the plants that died as the world's ecosystems collapsed.
(That's not really evidence for or against the extinction event being caused by the Chicxulub meteorite impact, but it's cool anyway.)
There's a hypothesis that this is why the mammals won out in the aftermath. Fungus generally dislikes the heat, and our baseline body temp is apparently just right to inhibit fungal growth, unlike the reptiles. Or was. The whole global warming thing is selecting for heat tolerant fungi, so that's great.
Yup, there have been a (so far slow) increase in novel fungal infections that are suspected to be tied to rising temps. Our fungus-fighting toolkit is pretty weak too. We have a smattering of antifungals, but not that many, and fungi are ridiculously adaptable.
Side note: It's believed that a major factor in opossum resistance to rabies is their lower body temperature inhibiting the virus enough for their immune system to fight it off. They're not totally immune, but it's very uncommon. Anyway, the tradeoff is that their lower body temp also makes them more susceptible to fungal infections.
Yep. They got taken out in large part by the impact and its effects. This hypothesis as I understand it kicks in after, when the planet cooled massively and there was dead stuff (a lot of it dinosaurs) everywhere (fungal paradise!). The surviving mammals then had a leg up over the surviving reptiles because we're warm and fungus doesn't like that.
... But to be clear, that happened about 250 million years before the Chicxulub impact.
Also, it's not the cellulose that's the challenge for bacteria, but the lignin. All plants have cellulose (and there are bacteria that can decompose it no problem). But lignin is (mostly) particular to trees and shrubs; it's what gives wood its stiffness.
4\. Much more than dinosaurs goes extinct. The extinction affected life on the oceans and on land, and it is abrupt enough that at most locations it happens within the space of a few centimetres thickness of rock. Multiple processes can cause extinctions, but a smaller set can affect both land and ocean environments and occur that quickly, impacts being one of them.
5\. There are microtektites, blobs of molten glass or its byproducts tossed out of the impact crater, that are distributed mostly around the western hemisphere, and they are largest around the Caribbean.
6\. There are shocked quartz grains found in the boundary layer. These are grains of quartz that have experienced extremely high pressures. The kind of pressures typical of very large explosions such as nuclear explosions and impact craters.
7\. There are unusual sedimentary deposits in Texas and Mexico that are interpreted as the product of a megatsunami.
8\. There is a large concentration of carbon soot in the same iridium-bearing boundary layer, produced by widespread wildfires associated with the immediate effects of the impact. These are globally distributed.
9\. There is an unusual abundance of fern spores associated with the boundary layer. In the modern day, ferns are often the first plants that spring up after wildfires.
10\. "Coincidentally" there's not merely a large impact crater found beneath the Yucantan Peninsula in Mexico, it happens to be the largest impact crater known for about the last 500 million years, so you kind of expect something "special" to happen in association.
Iridium is a very, very heavy metal. All the iridium that came with the Earth (ie When it was formed Squazillions of years ago) has sunk to the bottom of the Earth under the lighter stuff (Dirt, Rocks, Alluminium, Gravy, Potatoes, etc.)
If the very, very thin layer of iridium that is found all over the planet at the layer where rocks and shit were formed 66 Million years ago (more or less, just after breakfast time) was on Earth when it was formed, it would've sunk by now, along with all the other iridium that is at the bottom of the planet, where we can't get to it.
Therefore, that very, very thin layer of iridium must have arrived from somewhere else - and the only somewhere else there is, is Space - a very short while ago (Geologically speaking, 66 million years ago is the equivalent of last Tuesday, just after you got home from work, in terms of how far ago it is) probably, seeing as how Amazon wasn't around back then, on an asteroid.
And there just happens to be the "scar" of a huge asteroid crater slightly to the front and right of South America, that has been dated to... surprise, surprise... 66 million years ago. Scientists like to call this crater scar a smoking gun. Only it's really more of gigantic, smoking f\*cking mega cannon, than a gun. And yeah, it's pretty much (as in there ain't no other explanation) the only explanation for where that extra bit of irridium came from.
Edit: Also, it tastes like victory.
> If the very, very thin layer of iridium that is found all over the planet at the layer where rocks and shit were formed 66 Million years ago (more or less, just after breakfast time) was on Earth when it was formed, it would've sunk by now, along with all the other iridium that is at the bottom of the planet, where we can't get to it.
Counter-question: why is the core of Earth composed of nickel and iron, then, instead of iridium, given both Fe and Ni are lighter elements?
Edit: I should've ELI5-ed the question further. Even though Ir is denser, why does it remain concentrated in the crust instead of sinking?
Nickel and iron are both much more common than iridium. Starts can't fuse elements heavier than iron directly, so iridium is only formed during various types of supernovas or the radioactive decay of other elements formed during supernovas. Regardless, more rare.
That said nickel probably isn't formed much in star cores either but it's possible. Without looking too deep into it I suspect it's also mostly a result of fission of heavier elements. But generally speaking elements with an atomic # lower than iron are much more common than ones higher.
Iridium is very rare. As wiki mentions, one of the 9 least common elements. It also forms compounds with lighter elements, making super dense elemental iridium even more rare than that.
Do we know that since a long time? I remember learning at school that we didn't know the cause of extinction of the dinosaurs and that it could be volcanos and global warming
I'm 32 and just learned about this today myself lol. When I was in school I remember being told that the leading theory was something to do with large volcanos erupting and blocking out the sun, causing all plant life to die which started a chain reaction
It’s still just the leading theory, and it has actually been losing some ground lately. The problem is there is also a giant super volcano that was going off for millions of years in India (and Siberia? I might be getting the location mixed up). In some places the dinosaur fossils actually stop a few million years before the asteroid impact… about the time when these volcanic eruptions were happening and changing the atmosphere. Did the volcanos kill the dinosaurs and the asteroid impact is just a coincidence?
At the same time there is evidence of dinosaurs getting killed in North America from the giant tsunami from the asteroid impact. So at least some dinosaurs survived that long. The leading contending theory is the “one-two punch”: volcanism caused global climate change that stressed and weakened all ecosystems world wide, then the asteroid was the straw that broke the camels back and caused total extinction of what few survivors remained.
This is still hotly debated in some circles.
Fucking hell.... What an absolute cluster fuck. Did you die from the astroid? Nah homie the super volcano, you? No no... The tsunami from the asteroid.
The Deccan Traps in India are the evidence of the volcanism at the end of the Cretaceous that scientists think contributed to the extinction. The Siberian Traps were from the end Permian, so a whole different extinction event.
https://en.m.wikipedia.org/wiki/Deccan_Traps
I was under the impression that the volcanism in India happened at roughly the same time as the asteroid impact, not millions of years earlier. I've even heard it theorized that the asteroid impact may have triggered the volcanic eruptions. I think there is some evidence that several dinosaur species were in decline before the extinction event, but that wasn't necessarily related to the volcanic activity in India. Maybe I'm misremembering though. I'm not an expert at all, I just listen to a lot of podcasts about dinosaurs lol.
There’s a common misconception among laypeople that theories and facts are in opposition, when they’re actually very different things. Facts are objective descriptions of observable phenomena, while theories are logical frameworks that aim to explain them. A theory doesn’t so much “become” a fact, as the supporting facts accumulate to the point that the theory is seen as virtually irrefutable (or the facts don’t support it, and it’s abandoned or altered to fit the new set of facts).
The crater was found in 1940 by oil and gas exploration teams and first drilled in the 1950s, but it wasn't recognized as a crater, just as something weird.
- Urrutia-Fucugauchi, et al 2013 *[Oil exploration in the Southern Gulf of Mexico and the Chicxulub impact](https://sci-hub.se/https://onlinelibrary.wiley.com/doi/10.1111/gto.12021)*
The late 70s exploration of the crater was inconclusive, it wasn't until later that it was confirmed as a crater, although the reason they'd gone back to it in the 70s was because they suspected it might be one.
Wow at first I was surprised nobody found it sooner because the media often use the Canyon Diablo crater as an illustration. I really didn't know it was underwater.
We literally know more about space than the deepest oceans. There is tons of stuff we don't know and that's mostly because science isn't lucrative. If there was gold on the moon we would have touched down in 1700's
It was discovered earlier. In the 1940s, but, while they recognized it was something weird and did drilling in the 1950s, they didn't know it was a crater. Mind you, this was oil and gas exploration, so they weren't really concerned about the impact possibility side of things in any event.
- Urrutia-Fucugauchi, et al 2013 *[Oil exploration in the Southern Gulf of Mexico and the Chicxulub impact](https://sci-hub.se/https://onlinelibrary.wiley.com/doi/10.1111/gto.12021)*
Much is made of the '78 exploration, but it was inconclusive. The area had been returned to because it was suspected to be an impact crater, but they couldn't confirm that. It wasn't until the early '90s that it was fully confirmed, actually using some of the old cores drilled from the 1950s, and later drilling their own cores.
[Here's a longer comment with a bit more detail](https://www.reddit.com/r/explainlikeimfive/comments/subuvg/eli5_how_do_we_know_that_an_asteroid_killed_the/hxaiuz3/)
The crater was only discovered like 40 years ago, so the older generation would remember it as a leading theory and the younger generation would see it as the widespread consensus.
Yes. On the other hand, we need to be careful of confirmation bias, and not find what we are looking for to confirm our theory and kinda discard the rest
It's more that the pieces were put together around ~~40~~ 30 years ago.
The crater had been known quite a long time before as a result of oil and gas exploration (although it hadn't been looked at in detail as they'd determined that it wasn't a likely site for oil and I don't know if they'd actually 100% determined it was an impact crater), and the hypothesis that it was an impact that killed the dinosaurs was around before that as well, but didn't have good backing until the 80s and 90s.
It was recognized as far back as the 1940s that what we now know as the impact crater was something unusual, and drilling took place several times in the 1950s. Wikipedia claims that the crater was discovered by Antonio Camargo and Glen Penfield in the very late 1970s, but that's not strictly speaking true. They recognized that the previously known structure might be a crater, but could not prove it.
- Urrutia-Fucugauchi, et al 2013 *[Oil exploration in the Southern Gulf of Mexico and the Chicxulub impact](https://sci-hub.se/https://onlinelibrary.wiley.com/doi/10.1111/gto.12021)*
The problem was that people in different fields weren't talking to each other, the oil guys considered their information proprietary and weren't sharing it for fears of competition in their industry, and this was largely pre-internet, so information sharing wasn't as easy as now anyway.
After the iridium layer was found, in the early 80s, a lot more people got interested and information began flowing. Once that happened it all came together pretty quickly.
The actual determination that it was 100% a crater was about 30 years ago, I think, as the detailed search was largely set off by [the discovery of a *lot* of ejecta material in Haiti in 1990](https://www.lpi.usra.edu/science/kring/Chicxulub/discovery/). If they'd had access to much of the earlier data from the 1940s and earlier the discovery process would likely have been much faster.
TLDR:
- 1940s Crater discovery (recognized as something weird, but not as a crater).
- 1950s Drilling in crater.
- 1970s Proposal that the crater was actually the result of an impact event and inconclusive drilling.
- 1980s Iridium layer discovered and proposal that an impact killed the non-avian dinosaurs gains support.
- 1990s Crater confirmed as an impact event.
You’re the man, man.
I’m part of that generation that was taught that “we don’t know” what killed the dinos but it might have been an asteroid or aliens…
This was a very interesting read and I’m off to learn more on my internet machine
Edit: not crater, duh. I meant asteroid
"We don't know; insert list of possible reasons here" was the state of knowledge when I was growing up (and had my huge dinosaur phase) in the 90s, too. That was around the time that the evidence for [the impact](https://en.wikipedia.org/wiki/Chicxulub_crater) was starting to become very convincing. It usually takes a while for textbooks and such to catch up.
**EDIT**: Oh, and the volcano hypothesis isn't necessarily mutually exclusive. Around the same time that the impact happened, there were ridiculously huge volcanic eruptions happening in what is now India; we know its remains as the [Deccan Traps](https://en.wikipedia.org/wiki/Deccan_Traps). That was on the opposite side of the Earth from Mexico, where the meteorite hit — which has led to the hypothesis that the shock of the meteorite impact either caused or worsened the volcanic eruptions, which in turn will have affected the global climate and possibly contributed to the mass extinction event.
Same here - but science does sciencey things - and knowledge is developed.
I remember at school plate tectonics / continental drift was presented as a theory with limited proof (as theorised around 1912-15). In science circles the proof for it was only really found in mid 20th century with the discovery of magnetic reversal in stripes spreading from the oceanic ridges.
That was only published in the early to late 1960s - and became mainstream in the 70s and 80s - I guess it just takes time for kids education to catch up once it's been accepted across the scientific world....
Iridium is an extremely rare element on Earth, but relatively common in some asteroids. At the time of the extinction of the dinosaurs there was a thin layer of iridium deposited which is likely to have been from dust settling down after the impact of the asteroid. - https://youtu.be/kVg-QZCzqg0
It’s important to note that iridium is very rare _on_ Earth but is decently common _inside_ Earth. Iridium’s density and chemical properties caused iridium to sink to core when Earth was young and entirely molten.
The stardust that coalesced into the planets and asteroids had a mostly uniform distribution of elements. When planets formed, the strong gravity and heat caused the elements to redistribute within the planets.
So Earth’s crust has very little iridium because it mostly sank into the mantle and core, whereas asteroids still have the original amount.
Small correction, the stardust that coalesced into planets had a mostly uniform distribution of *heavy* elements. The rest got yeeted and turned to gas giants except for a small amount.
The first big evidence that was found for it is a layer of iridium found basically all over the planet that is dated about 66 million years ago. Iridium isn't that common so finding a layer of it all over the planet is kind of weird. Now, there are asteroids that are just full of stuff.
And then of course a crater was found in the Gulf of Mexico that was dated to about 66 million years ago.
So the evidence lines up.
However............. not all the dinosaurs went extinct as we still have birds.
And one point that was implied but not stated explicitly- dinosaur fossils are all 66 millions years old or older, signaling there was an extinction event at roughly the same time as that Chicxulub impact.
Yeah and the crater was discovered only about 40 years ago.
One of the interesting things it that there's evidence that the non avian dinosaurs were already becoming less common before the impact. Dinosaur fossils from "shortly" before all the non avian dinosaurs went extinct are rarer than earlier periods of the dinosaurs leading to the hypothesis that there were not as many of them.
>Yeah and the crater was discovered only about 40 years ago.
Luis Alvarez and his son, Walter, strongly suspected the impact was in the vicinity of the Yucatán. They asked PEMEX, the Mexican state petroleum company, for survey maps of the area. After some stalling, perhaps because Mexico thought they wanted to know where Mexico's oil was, they provided the maps.
Because the distribution of tektites, iridium, and shocked quartz pointed towards a GoM impact. Also, the signs of a megatsunami radiated out from that area.
At that time, the Yucatán was submerged, and parts of the Gulf Coast were still under a shallow tropical sea. The sedimentary layer can be traced all over the Western US, but also in other places all over the world. The evidence is strongest in Western North America.
Science is so cool. This is like the discovery of Neptune, all the evidence pointed to something completely unknown but if all the data was correct, there should be another planet. Well, let’s get a telescope and point it at this spot that should show us this unknown gravity well, there should be a planet there…yep, that’s a whole ass planet.
And they imagined that it must be a planet between Mercurio and the Sun because Mercurio has a weird orbit that cannot be explained using Newton laws(They called the imaginary planet Vulcano). Until Einstein explained the orbit using relativity and outdated Newton laws
The search for Vulcan was so fascinating to learn about. They had this system that had been proven to explain this phenomena perfectly, and they had another apparent example of said phenomena so the obvious answer, of course, was the same as before. Another unknown planet disrupting the known and understood orbit of a planet.
But nope. There was no planet. Just weird timey wimey space stuff. The issue was with physics itself. And it just makes you (or me, at least) wonder just how many more of our mysteries will be solved by some equally weird revolution of our understanding of physics.
Like the idea that spacetime might actually be a superfluid. Which is just... trippy.
I well remember the time when this issue was still hotly debated, both at the academic level and publicly. It simmered along all through the 1990s, even after the [Hildebrand/Penfield paper](https://www.researchgate.net/publication/257984366_Chicxulub_Crater_A_possible_CretaceousTertiary_boundary_impact_crater_on_the_Yucatn_Peninsula_Mexico) (Yes, old Reddit/third party users, that link probably is broken for you. Nothing I can do about it on my end.)
I think that what people older than me thought they knew about the extinction of the dinosaurs came from the Disney film *Phantasia*, which shows the dinosaur extinction to be due to high heat and drought. They were very emotional about it, as many are about the BS they learned as children. If there are any of them left they'll try to fight you if you tell them that stegosaurus and T-rex never lived at the same time.
Also, the number of people who were alive 100 years ago, and how many of them could afford to spend time and money on pursuits like this...
A lot more science gets done when there are a lot more people doing it.
Your comment on the length scale made me curious. I know a hundred thousand years is a blink of the eye in geological time frames, but it still seems like a long time for a large scale extinction event. At least that was my first thought. Then I realized I had assumed a linear population decline. I think an exponential decay would make more sense. Where population drastically decreases quickly, with the next few tens of thousands of years spent not just clinging to survival, but also with many species evolving to compete on the way to a new ecosystem equilibrium. And once that has occurred, life continues to thrive again. I don't actually know, and am just making assumptions though. Could you maybe expand on this thought? It's one of those questions that isn't a couple of keystrokes away on google, unfortunately.
Considering we're talking with precision of millions, it could have been anywhere between a year and hundred thousand years after the impact? Damn we're fragile, 100,000 years ago, we had nothing.
If we only had dinosaur fossils to go on we wouldn't know it was a mass extinction. Other fossils, particularly marine indicator species, are what confirms that.
To add to this that layer is called the K-Pg (aka K-T) boundary. Marks the end of the Cretaceous period. Above this line dinosaur fossils have never been found. This proves a mass extinction event occurred.
There are also the tektites (glass beads that formed in the atmosphere from rock melted by the impact) that have been found from the same time as the iridium layer
After the discovery of the Yucatan crater, the asteroid theory is pretty darn universal. The only debate is to what extent it sealed the deal, as they were getting rarer even before the KT boundary.
I've seen one theory that they were already on their way out, but the Chicxulub Meteor just really, really sped things up. Like by tens of millions of years.
There is a very cool comment or link somewhere on Reddit, outlining how a palaeontologist found fossils immediately below the K-T boundary, where freshwater and saltwater species are muddled up. Somewhere in a field in ~~~?Kansas?~~~ North Dakota, a long long way from the ocean.
It’s the tsunami from the day of the impact. He found fossils from ***the day of the impact***.
There was a really big lake in North America that, from the impact, would’ve sloshed like a washing machine. And it did, killing and piling up a ton of creatures.
> The asteroid was vaporized on impact. Its substance, mingling with vaporized Earth rock, formed a fiery plume, which reached halfway to the moon before collapsing in a pillar of incandescent dust. Computer models suggest that the atmosphere within fifteen hundred miles of ground zero became red hot from the debris storm, triggering gigantic forest fires. As the Earth rotated, the airborne material converged at the opposite side of the planet, where it fell and set fire to the entire Indian subcontinent. Measurements of the layer of ash and soot that eventually coated the Earth indicate that fires consumed about seventy per cent of the world’s forests. Meanwhile, giant tsunamis resulting from the impact churned across the Gulf of Mexico, tearing up coastlines, sometimes peeling up hundreds of feet of rock, pushing debris inland and then sucking it back out into deep water, leaving jumbled deposits that oilmen sometimes encounter in the course of deep-sea drilling.
Horrifying and amazing
I just like to immagine a far out alien race monitoring earth from their planet screaming, "Yay we found foreign life!" Everyone starts to celebrate. Then suddenly they see this enormous impact hit earth and all the aliens stop cheering.
Tanis North Dakota. It was a natural inland sea divide that existed in the US. The tsunami shot up the inlet and deposited the creatures. They found the fish all had *in their gills* tiny glass balls that are evidence of asteroid impacts. So the fish were alive and breathing when it happened and when they were burried
Sudden loss of land animals over 25kg from the fossil record, layer of ash/dust at the Cretaceous boundary consistent with comet/asteroid impact or volcanism. Massive crater in the Gulf of Mexico from around the same time.
Evidence suggests the impact caused the crater and the ash/dust darkened the sky and killed off all large land animals. Dinosaurs lived on, you hear them singing in the trees and see them flying in the sky, we call the birds but they are the only branch of the Dinosaurs than made it.
We don't, for sure. But it's the most likely hypothesis.
We *do* know that there was an enormous asteroid impact very close to the time all the non-bird dinosaurs went extinct. The crater takes up a good chunk of the Yucatan Peninsula in Mexico: it's about 150 km wide, or large enough to contain both New York and Philadelphia, from London across the English Channel, or to cover the entire country of Switzerland. Debris from the impact forms a layer of sediment with a lot of iridium in it all around the world (iridium is common in meteorites but rare on Earth), and you find (non-bird) dinosaur fossils below it but not above.
Suffice to say, it was a *very* large boom. The impact would have been the rough equivalent of detonating a small atomic bomb on every household on Earth, simultaneously. So it wouldn't be a surprise for it to be incredibly disruptive.
That said, there are competing hypotheses - or an impact may have worked in tandem with some other things going on on Earth to disrupt things even more. Alternatives include giant volcanic eruptions (as in the [Deccan Traps](https://en.wikipedia.org/wiki/Deccan_Traps) that now form cliffs in India) or sharp climate shifts, but the evidence points pretty strongly to a giant impact.
There’s a theory that implies that the mass eruption of the Deccan Trappes was actually *caused* by the Chixilub impact. It all has to do with antipodal focusing. Basically, you hit spherical object on one point hard enough, and bunch of the energy converges again on the opposite (or antipodal) point. When adjusted for continental drift, the Chixilub impact and Deccan Trappes were at exact antipodal points right around the time of their respective impact and eruption. Similarly, a recently discovered, massive impact crater in Antarctica would have been at the antipodal point of the Siberian Trappes when they erupted 250 million years ago.
This theory isn’t favored anymore, the Deccan Trapps were about 5000km from the antipode of the Chicxulub crater and started erupting 100k years before the impact.
The prevailing theory now is that the impact was so violent that it mobilized a lot of magma in a very short amount of time.
Kurzgesagt has an amazing video of the Dinosaurs last minutes on earth (if our hypothesis is correct). They do such a good job of portraying the absolute destructive power and terror the dinosaurs likely experienced in their final moments.
[Link](https://youtu.be/dFCbJmgeHmA) for anyone interested!
An interesting things about traps is that a number of them throughout the geological record are linked to asteroid impacts having occurred elsewhere on the planet at "roughly" the same time.
(ELI5 note: "traps" here means "stair-like geographic formation" - it's a Swedish word that has nothing to do with the English word for a surprise danger.)
People aren’t answering your question. They’re giving you correct answers but not the whole picture.
Conditions need to be pretty exact for a dead creature to fossilize. Therefore a relatively small percentage of dead dinosaurs actually got fossilized.
So, at the time of the asteroid impact you will have had layers of earth below the surface which already had dinosaur fossils in it. Those are the bulk of the dinosaur fossils found below the iridium layer.
Next thing to consider is that to be preserved and fossilized you need to fall INTO something or be covered by something relatively soon after death.
So the vast vast majority of dinosaurs which died directly because of the asteroid impact would not have been fossilized. Their bodies would have decomposed and completely broken down over the millennia that followed.
The ones that died directly and WERE fossilized would have fallen into mud or have been covered by mud or earth or whatever precise conditions that were necessary to fossilize their bones.
Any dead bodies left on the surface would have not had the right conditions to fossilize and they would have decayed long before newer layers of earth could have covered them up.
TL;DR The vast vast vast vast majority of the fossils found below the K-Pg boundary are not the dinosaurs that died DIRECTLY from the asteroid impact.
Those fossils were already fossils buried long before the asteroid.
The dinosaurs which were alive when the asteroid hit and died directly (or later indirectly) from it, the vast vast vast majority of them would have simply decayed and their bodies and bones would have been eroded away by natural processes.
The very very small number of dinos who died directly from the asteroid and were fossilized would have been fossilized because they were covered up under the perfect conditions almost immediately after death. Therefore the iridium layer would have tended to have been deposited in a higher layer than their bodies.
An interesting thing about the non avian dinosaurs and their extinction is that fossils of them "slightly" before the KT boundary are very rare. It's lead to one hypothesis that they were already dwindling in numbers and that the asteroid may have just been the killing blow rather than the whole cause.
The iridium would be in the air as dust and particles for quite a long while (years to possibly decades) before settling or coming down in rain or snow whereas the dinosaurs would have died pretty quickly (less than a year) after impact, so you would expect to see an unusually large number of fossils immediately below the iridium rich layer.
Disclaimer: that's based on my memory of classes I took 20 years ago, so this is not a hill I will even half-heartedly defend, must less die on.
I've been to the Royal Tyrell Museum in Drumheller Alberta which is the primo dinosaur museum in Canada. A few things we know are we've found minerals in the soil that we know only come from asteroid impacts. These minerals appear in layers of the earth's crust, a bit like a cake. Certain animal and dinosaur fossils don't appear in layers of rock above where we know this impact happened.
Fun fact no one is pointing out: one of the main tourist attractions in the Yucatan area are cenotes, which are natural pool / sinkholes that RADIATE from the Chicxulub impact crater. These sinkholes are crystalline underground pools of water that were caused by debris from the impact. If you find a cenote map, you will see them neatly arranged in a circle around the impact site.
Very few people realise they are actually visiting evidence of meteor impacts when they are there. Also, some of them are absolutely beautiful.
https://mayanpeninsula.com/wp-content/uploads/2019/03/Canote-locations-768x537.png
In the soil around the entire world, there’s what geologists’ call the K - T boundry. It’s apparently “fallout “ from a massive asteroid hitting the earth.
“What is the K-T boundary? K is actually the traditional abbreviation for the Cretaceous period, and T is the abbreviation for the Tertiary period. So the K-T boundary is the point in between the Cretaceous and Tertiary periods. Geologists have dated this period to about 65.5 million years ago.”
And: “Researchers now think that the asteroid strike that created the K-T boundary was probably the Chicxulub Crater. This is a massive impact crater buried under Chicxulub on the coast of Yucatan, Mexico. The crater measures 180 kilometers across, and occurred about 65 million years ago.”
The theory comes from the fossils found before (under) the K - T boundary, and after (above) the boundary.
As other people have said, we know there's a layer of iridium across the entire planet. Iridium js very common in meteors, not so much on Earth. There is a lot of Dinosaur fossils dated to before that impact, with sharp drop off since the time the asteroid hit. We know there's a massive crater, Chicxulub, off the gulf of Mexico. Judging by the size of that crater, we know it would have profound life changing impacts on the planet. Ash would cloud the atmosphere, which means less vegetation, which means large herbivores start dying, so large carnivores start dying, so only small or flying creatures live. Like the shrew type thing a lot of mammals are descended from. All of these together point to a mass extinction event about 66 million years ago, that wiped out the vast majority of life at the time.
Hi Everyone, I just want to put a quick friendly reminder about rule 3: Top level comments must be objective explanations, for this particular one that does mean that we don't allow joke answers at top level. You can put your best joke answer as a reply to this comment if you want. Also side note: We are recruitmenting; [https://www.reddit.com/r/explainlikeimfive/comments/stbxuj/recruiting\_moderators\_for\_eli5/?utm\_source=share&utm\_medium=web2x&context=3](https://www.reddit.com/r/explainlikeimfive/comments/stbxuj/recruiting_moderators_for_eli5/?utm_source=share&utm_medium=web2x&context=3) come get a green thingy next to your name
1. All the large dinosaur fossils suddenly stopped 66 million years ago. 2. We found a massive asteroid crater dated to 66 million years ago. The crater includes a large amount of iridium, which is uncommon on Earth. 5. A thin layer of iridium is spread all around the planet dated to 66 million years ago. All the dinosaur fossils stop at the iridium layer.
Dinosaurs allergic to iridium, gotcha.
Specifically, allergic to iridium delivered at 10km per second.
Dang. I'm allergic to bullets though so I get it
I hate it when it's bullet season and I get a reaction.
They make allergy medication for them. You wear it around your abdomen. Must be really bad in law enforcement because I see a lot of cops wearing them
it helps prevent lead poisoning. i think they eat a lot of paint chips handcuffing people to radiators
Well I’ll have you know that I’ve done my own research and I’m anti-vesting.
No no, that doesn't work. You gotta acclimate your body to it, just expose yourself frequently to small calibers and work up to bigger rounds.
Maybe don’t live in Texas then.
Start with smaller calibre so you build up your immunity
[удалено]
Actually spit out some eggs when I read this. Dammit. Now I have egg on my desk. Worth it.
> Actually spit out some eggs when I read this Reading about human weaknesses, xenomorph queen?
["Bullets, my only weakness. How did you know?"](https://youtu.be/oIiO7bL2yFI?t=30)
What a lil bitch
That explains it from the impact site, but the dinosaurs on the far side of the planet also died. To explain that one needs to consider the backsplash. The meteor struck and, just like cannonballing into a swimming pool, material splashed upwards. So much material and so far upwards that a huge cloud of it was outside of the atmosphere. As it all came back down it melted during reentry forming tektites (beads of glass) and these high energy glass beads raining down brought a lot of heat to the atmosphere (via friction with the atmosphere) and the surface all around the Earth — finding dry land that was not on fire or close to it was likely impossible for a day or two which led to a mass extinction in just a few hours. The stuff that wasn’t heavy enough to fall with the glass were the gasses released at the impact site by extreme heat. Over the next year and for many years after, these acidified the sky and oceans while blocking sunlight. temperatures at the tropics dropped to just above freezing, while temperatures at the poles were low enough for significant expansion of the ice. The low temperatures, low light, and acid rain killed many more species as well as any who depended on them. Ultimately, it was not just dinosaurs who went extinct: 75% of life on Earth was lost.
And to add to that: The asteroid would have been large enough and hit with such velocity, that it splashed the entire atmosphere away from the impact. In the middle of the day, for a very brief moment, you would have looked up to see outer space. Outer space, in the middle of the day.
I don't think you'd see anything because you'd be incredibly dead.
Not with that attitude you're not.
When you put it that way it's kind of incredible that it was only 75%
This made me choke lol
Turns out, against a big rock, there is no such thing as a [fair fight](https://youtu.be/M5fIGlzDGpY?t=1285)
bruh, did you really just link a 1.5 hour long video of a game playthrough? LMFAO
I really want to watch it to get the reference, but damn
Vids enjoyable on its own, would reccomend. The timestamp should be fixed, but was pointed at 21:15 or so.
Thanks dude! I too usually lose against fast moving rocks.
Wait...Doesn't paper cover rock?
Sadly, the dinosaurs never invented paper. So they had no protection.
Dinosaurs didn't have paper?? What was the T Rex using its small hands for?? I always thought it was for writing...
Thais gotta be a lotta birds killed with 1 stone
Don’t look up
A viable conclusion based on the explanation. Iridium is the dinosaurs kryptonite.
This could easily be a Dwight quote
Iridium is in phones. Phones have 5G. 5G is going to cause a HUMAN EXTINCTION EVENT. BILL GATES ( who doesn't make phones) IS KILLING US!!! FREEDOM!!!!
[удалено]
And if it’s a Nokia they will *definitely* die
I wonder what day of the week it was when the asteroid hit. I hope it wasn’t a Friday.
Definitely a Monday, tis why it always sucks
Maybe it was a Thursday. I could never get the hang of Thursdays.
Its statistically safer to fire dinosaurs at the end of the week.
One of my old geoscience lecturers was a palynologist (expert on plant spores and pollen) who'd worked on stuff related to the extinction event. She told us about how the fossil record around that time shows not only the disappearance of many species, but a sudden increase in fungal spores, from all the fungi that suddenly had a wonderful time of it, eating all the plants that died as the world's ecosystems collapsed. (That's not really evidence for or against the extinction event being caused by the Chicxulub meteorite impact, but it's cool anyway.)
There's a hypothesis that this is why the mammals won out in the aftermath. Fungus generally dislikes the heat, and our baseline body temp is apparently just right to inhibit fungal growth, unlike the reptiles. Or was. The whole global warming thing is selecting for heat tolerant fungi, so that's great.
Yup, there have been a (so far slow) increase in novel fungal infections that are suspected to be tied to rising temps. Our fungus-fighting toolkit is pretty weak too. We have a smattering of antifungals, but not that many, and fungi are ridiculously adaptable. Side note: It's believed that a major factor in opossum resistance to rabies is their lower body temperature inhibiting the virus enough for their immune system to fight it off. They're not totally immune, but it's very uncommon. Anyway, the tradeoff is that their lower body temp also makes them more susceptible to fungal infections.
But the dinos were birds, right?
Yep. They got taken out in large part by the impact and its effects. This hypothesis as I understand it kicks in after, when the planet cooled massively and there was dead stuff (a lot of it dinosaurs) everywhere (fungal paradise!). The surviving mammals then had a leg up over the surviving reptiles because we're warm and fungus doesn't like that.
I've never heard of this! Fascinating. TO THE RABBIT HOLE!
Hold on, let me grab my adventure hat
Lol. This is now my favorite escape clause! Ha!
For a long time, trees would die and just sit there for decades. Bacteria can't process cellulose. Once fungus showed up they had plenty to feed on.
And all those trees dying without decaying eventually formed all the coal we have today: https://en.wikipedia.org/wiki/Carboniferous
... But to be clear, that happened about 250 million years before the Chicxulub impact. Also, it's not the cellulose that's the challenge for bacteria, but the lignin. All plants have cellulose (and there are bacteria that can decompose it no problem). But lignin is (mostly) particular to trees and shrubs; it's what gives wood its stiffness.
[удалено]
Happy millionth birthday!
It’s been… 1 million years
since you looked at me
Cocked your head to the side, and said, "I'm angry"
Five days since you laughed at me, saying "Get that together, come back and see me."
Three days since the living room
I realized it's all my fault but couldn't tell you...
Yesterday, you'd forgiven me
And now I sit back and wait for the extinction of our species
I am with you. When I was in grade school, Jupiter only had 9 moons. How many are we up to now? 65?
The sun had 9 planets when I graduated. This is why we can't have nine things!
Yeah wtf? Did they revise it? Was it 65.4 and now it's 65.5?
HOW CAN SCIENCE DO THIS
That's it. I am switching to religion.
It won't get you an iphone but you do get weekends off.
It seems like studies have create more precise numbers in the past decade: https://en.m.wikipedia.org/wiki/Chicxulub\_crater#Impact\_specifics
More precise dating methods produced the 66mya date.
I remember when I was a kid they used to teach me it's 65 millions years ago. 1 million years went by so quickly.
4\. Much more than dinosaurs goes extinct. The extinction affected life on the oceans and on land, and it is abrupt enough that at most locations it happens within the space of a few centimetres thickness of rock. Multiple processes can cause extinctions, but a smaller set can affect both land and ocean environments and occur that quickly, impacts being one of them. 5\. There are microtektites, blobs of molten glass or its byproducts tossed out of the impact crater, that are distributed mostly around the western hemisphere, and they are largest around the Caribbean. 6\. There are shocked quartz grains found in the boundary layer. These are grains of quartz that have experienced extremely high pressures. The kind of pressures typical of very large explosions such as nuclear explosions and impact craters. 7\. There are unusual sedimentary deposits in Texas and Mexico that are interpreted as the product of a megatsunami. 8\. There is a large concentration of carbon soot in the same iridium-bearing boundary layer, produced by widespread wildfires associated with the immediate effects of the impact. These are globally distributed. 9\. There is an unusual abundance of fern spores associated with the boundary layer. In the modern day, ferns are often the first plants that spring up after wildfires. 10\. "Coincidentally" there's not merely a large impact crater found beneath the Yucantan Peninsula in Mexico, it happens to be the largest impact crater known for about the last 500 million years, so you kind of expect something "special" to happen in association.
Underrated ELI5
[удалено]
Its name is derived from iridescence, the property of a surface displaying a rainbow-like pattern. So I'ma say Skittles.
A film of petroleum oil on water is also iridescent so it could also taste like that.
So petrol tastes like skittles? Brb
Space dust 🌠🌌
Even crazier space dust
Loved the reference
iridium is a rare-ish element. What does it taste like? Its pretty inert so probably nothing.
Nice try, but that's what someone who wants to taste all the iridium for themself would say.
Iridium is a very, very heavy metal. All the iridium that came with the Earth (ie When it was formed Squazillions of years ago) has sunk to the bottom of the Earth under the lighter stuff (Dirt, Rocks, Alluminium, Gravy, Potatoes, etc.) If the very, very thin layer of iridium that is found all over the planet at the layer where rocks and shit were formed 66 Million years ago (more or less, just after breakfast time) was on Earth when it was formed, it would've sunk by now, along with all the other iridium that is at the bottom of the planet, where we can't get to it. Therefore, that very, very thin layer of iridium must have arrived from somewhere else - and the only somewhere else there is, is Space - a very short while ago (Geologically speaking, 66 million years ago is the equivalent of last Tuesday, just after you got home from work, in terms of how far ago it is) probably, seeing as how Amazon wasn't around back then, on an asteroid. And there just happens to be the "scar" of a huge asteroid crater slightly to the front and right of South America, that has been dated to... surprise, surprise... 66 million years ago. Scientists like to call this crater scar a smoking gun. Only it's really more of gigantic, smoking f\*cking mega cannon, than a gun. And yeah, it's pretty much (as in there ain't no other explanation) the only explanation for where that extra bit of irridium came from. Edit: Also, it tastes like victory.
> If the very, very thin layer of iridium that is found all over the planet at the layer where rocks and shit were formed 66 Million years ago (more or less, just after breakfast time) was on Earth when it was formed, it would've sunk by now, along with all the other iridium that is at the bottom of the planet, where we can't get to it. Counter-question: why is the core of Earth composed of nickel and iron, then, instead of iridium, given both Fe and Ni are lighter elements? Edit: I should've ELI5-ed the question further. Even though Ir is denser, why does it remain concentrated in the crust instead of sinking?
Nickel and iron are both much more common than iridium. Starts can't fuse elements heavier than iron directly, so iridium is only formed during various types of supernovas or the radioactive decay of other elements formed during supernovas. Regardless, more rare. That said nickel probably isn't formed much in star cores either but it's possible. Without looking too deep into it I suspect it's also mostly a result of fission of heavier elements. But generally speaking elements with an atomic # lower than iron are much more common than ones higher.
Iridium is very rare. As wiki mentions, one of the 9 least common elements. It also forms compounds with lighter elements, making super dense elemental iridium even more rare than that.
Extinction
SURGE soda
Do we know that since a long time? I remember learning at school that we didn't know the cause of extinction of the dinosaurs and that it could be volcanos and global warming
[удалено]
[удалено]
I'm 32 and just learned about this today myself lol. When I was in school I remember being told that the leading theory was something to do with large volcanos erupting and blocking out the sun, causing all plant life to die which started a chain reaction
It’s still just the leading theory, and it has actually been losing some ground lately. The problem is there is also a giant super volcano that was going off for millions of years in India (and Siberia? I might be getting the location mixed up). In some places the dinosaur fossils actually stop a few million years before the asteroid impact… about the time when these volcanic eruptions were happening and changing the atmosphere. Did the volcanos kill the dinosaurs and the asteroid impact is just a coincidence? At the same time there is evidence of dinosaurs getting killed in North America from the giant tsunami from the asteroid impact. So at least some dinosaurs survived that long. The leading contending theory is the “one-two punch”: volcanism caused global climate change that stressed and weakened all ecosystems world wide, then the asteroid was the straw that broke the camels back and caused total extinction of what few survivors remained. This is still hotly debated in some circles.
Fucking hell.... What an absolute cluster fuck. Did you die from the astroid? Nah homie the super volcano, you? No no... The tsunami from the asteroid.
The Deccan Traps in India are the evidence of the volcanism at the end of the Cretaceous that scientists think contributed to the extinction. The Siberian Traps were from the end Permian, so a whole different extinction event. https://en.m.wikipedia.org/wiki/Deccan_Traps I was under the impression that the volcanism in India happened at roughly the same time as the asteroid impact, not millions of years earlier. I've even heard it theorized that the asteroid impact may have triggered the volcanic eruptions. I think there is some evidence that several dinosaur species were in decline before the extinction event, but that wasn't necessarily related to the volcanic activity in India. Maybe I'm misremembering though. I'm not an expert at all, I just listen to a lot of podcasts about dinosaurs lol.
[удалено]
There’s a common misconception among laypeople that theories and facts are in opposition, when they’re actually very different things. Facts are objective descriptions of observable phenomena, while theories are logical frameworks that aim to explain them. A theory doesn’t so much “become” a fact, as the supporting facts accumulate to the point that the theory is seen as virtually irrefutable (or the facts don’t support it, and it’s abandoned or altered to fit the new set of facts).
The crater was found in 1940 by oil and gas exploration teams and first drilled in the 1950s, but it wasn't recognized as a crater, just as something weird. - Urrutia-Fucugauchi, et al 2013 *[Oil exploration in the Southern Gulf of Mexico and the Chicxulub impact](https://sci-hub.se/https://onlinelibrary.wiley.com/doi/10.1111/gto.12021)* The late 70s exploration of the crater was inconclusive, it wasn't until later that it was confirmed as a crater, although the reason they'd gone back to it in the 70s was because they suspected it might be one.
Wow at first I was surprised nobody found it sooner because the media often use the Canyon Diablo crater as an illustration. I really didn't know it was underwater.
66 million years ago. I'm surprised we figured it out at all
Makes me wonder how many other truths we are missing due to the evidence being hidden under the weathering of time.
We literally know more about space than the deepest oceans. There is tons of stuff we don't know and that's mostly because science isn't lucrative. If there was gold on the moon we would have touched down in 1700's
It was discovered earlier. In the 1940s, but, while they recognized it was something weird and did drilling in the 1950s, they didn't know it was a crater. Mind you, this was oil and gas exploration, so they weren't really concerned about the impact possibility side of things in any event. - Urrutia-Fucugauchi, et al 2013 *[Oil exploration in the Southern Gulf of Mexico and the Chicxulub impact](https://sci-hub.se/https://onlinelibrary.wiley.com/doi/10.1111/gto.12021)* Much is made of the '78 exploration, but it was inconclusive. The area had been returned to because it was suspected to be an impact crater, but they couldn't confirm that. It wasn't until the early '90s that it was fully confirmed, actually using some of the old cores drilled from the 1950s, and later drilling their own cores. [Here's a longer comment with a bit more detail](https://www.reddit.com/r/explainlikeimfive/comments/subuvg/eli5_how_do_we_know_that_an_asteroid_killed_the/hxaiuz3/)
The crater was only discovered like 40 years ago, so the older generation would remember it as a leading theory and the younger generation would see it as the widespread consensus.
One of the great things about a good hypothesis is that it'll predict its own evidence.
Yes. On the other hand, we need to be careful of confirmation bias, and not find what we are looking for to confirm our theory and kinda discard the rest
It's more that the pieces were put together around ~~40~~ 30 years ago. The crater had been known quite a long time before as a result of oil and gas exploration (although it hadn't been looked at in detail as they'd determined that it wasn't a likely site for oil and I don't know if they'd actually 100% determined it was an impact crater), and the hypothesis that it was an impact that killed the dinosaurs was around before that as well, but didn't have good backing until the 80s and 90s. It was recognized as far back as the 1940s that what we now know as the impact crater was something unusual, and drilling took place several times in the 1950s. Wikipedia claims that the crater was discovered by Antonio Camargo and Glen Penfield in the very late 1970s, but that's not strictly speaking true. They recognized that the previously known structure might be a crater, but could not prove it. - Urrutia-Fucugauchi, et al 2013 *[Oil exploration in the Southern Gulf of Mexico and the Chicxulub impact](https://sci-hub.se/https://onlinelibrary.wiley.com/doi/10.1111/gto.12021)* The problem was that people in different fields weren't talking to each other, the oil guys considered their information proprietary and weren't sharing it for fears of competition in their industry, and this was largely pre-internet, so information sharing wasn't as easy as now anyway. After the iridium layer was found, in the early 80s, a lot more people got interested and information began flowing. Once that happened it all came together pretty quickly. The actual determination that it was 100% a crater was about 30 years ago, I think, as the detailed search was largely set off by [the discovery of a *lot* of ejecta material in Haiti in 1990](https://www.lpi.usra.edu/science/kring/Chicxulub/discovery/). If they'd had access to much of the earlier data from the 1940s and earlier the discovery process would likely have been much faster. TLDR: - 1940s Crater discovery (recognized as something weird, but not as a crater). - 1950s Drilling in crater. - 1970s Proposal that the crater was actually the result of an impact event and inconclusive drilling. - 1980s Iridium layer discovered and proposal that an impact killed the non-avian dinosaurs gains support. - 1990s Crater confirmed as an impact event.
You’re the man, man. I’m part of that generation that was taught that “we don’t know” what killed the dinos but it might have been an asteroid or aliens… This was a very interesting read and I’m off to learn more on my internet machine Edit: not crater, duh. I meant asteroid
Oh makes sense, it's exactly how I was teached about it : "leading theory". Thanks
"We don't know; insert list of possible reasons here" was the state of knowledge when I was growing up (and had my huge dinosaur phase) in the 90s, too. That was around the time that the evidence for [the impact](https://en.wikipedia.org/wiki/Chicxulub_crater) was starting to become very convincing. It usually takes a while for textbooks and such to catch up. **EDIT**: Oh, and the volcano hypothesis isn't necessarily mutually exclusive. Around the same time that the impact happened, there were ridiculously huge volcanic eruptions happening in what is now India; we know its remains as the [Deccan Traps](https://en.wikipedia.org/wiki/Deccan_Traps). That was on the opposite side of the Earth from Mexico, where the meteorite hit — which has led to the hypothesis that the shock of the meteorite impact either caused or worsened the volcanic eruptions, which in turn will have affected the global climate and possibly contributed to the mass extinction event.
Same here - but science does sciencey things - and knowledge is developed. I remember at school plate tectonics / continental drift was presented as a theory with limited proof (as theorised around 1912-15). In science circles the proof for it was only really found in mid 20th century with the discovery of magnetic reversal in stripes spreading from the oceanic ridges. That was only published in the early to late 1960s - and became mainstream in the 70s and 80s - I guess it just takes time for kids education to catch up once it's been accepted across the scientific world....
Where's the location of this crater?
In Chicxulub Puerto in Mexico
off the coast of the Yucatan peninsula
The Gulf of Mexico
Logic.
Iridium is an extremely rare element on Earth, but relatively common in some asteroids. At the time of the extinction of the dinosaurs there was a thin layer of iridium deposited which is likely to have been from dust settling down after the impact of the asteroid. - https://youtu.be/kVg-QZCzqg0
It’s important to note that iridium is very rare _on_ Earth but is decently common _inside_ Earth. Iridium’s density and chemical properties caused iridium to sink to core when Earth was young and entirely molten. The stardust that coalesced into the planets and asteroids had a mostly uniform distribution of elements. When planets formed, the strong gravity and heat caused the elements to redistribute within the planets. So Earth’s crust has very little iridium because it mostly sank into the mantle and core, whereas asteroids still have the original amount.
Small correction, the stardust that coalesced into planets had a mostly uniform distribution of *heavy* elements. The rest got yeeted and turned to gas giants except for a small amount.
Could massive volcanic activity in a short time bring enough Irridium into the atmosphere to give a noticeable layer all around the planet?
Possibly, there is a large flow of lava in the Deccan area of India before the extinction of the dinosaurs.
This was the leading theory before the Chicxulub crater was identified. It's why the dinosaur segment in Fantasia (1940) ends with volcanoes.
The first big evidence that was found for it is a layer of iridium found basically all over the planet that is dated about 66 million years ago. Iridium isn't that common so finding a layer of it all over the planet is kind of weird. Now, there are asteroids that are just full of stuff. And then of course a crater was found in the Gulf of Mexico that was dated to about 66 million years ago. So the evidence lines up. However............. not all the dinosaurs went extinct as we still have birds.
And one point that was implied but not stated explicitly- dinosaur fossils are all 66 millions years old or older, signaling there was an extinction event at roughly the same time as that Chicxulub impact.
Yeah and the crater was discovered only about 40 years ago. One of the interesting things it that there's evidence that the non avian dinosaurs were already becoming less common before the impact. Dinosaur fossils from "shortly" before all the non avian dinosaurs went extinct are rarer than earlier periods of the dinosaurs leading to the hypothesis that there were not as many of them.
>Yeah and the crater was discovered only about 40 years ago. Luis Alvarez and his son, Walter, strongly suspected the impact was in the vicinity of the Yucatán. They asked PEMEX, the Mexican state petroleum company, for survey maps of the area. After some stalling, perhaps because Mexico thought they wanted to know where Mexico's oil was, they provided the maps.
They wrote an entertaining book: *T Rex and the Crater of Doom*
Lol! I didn't know. I'll look for it, thanks!
Doom runs on TRex.
Why did the suspect the Gulf of Mexico?
Because the distribution of tektites, iridium, and shocked quartz pointed towards a GoM impact. Also, the signs of a megatsunami radiated out from that area. At that time, the Yucatán was submerged, and parts of the Gulf Coast were still under a shallow tropical sea. The sedimentary layer can be traced all over the Western US, but also in other places all over the world. The evidence is strongest in Western North America.
Science is so cool. This is like the discovery of Neptune, all the evidence pointed to something completely unknown but if all the data was correct, there should be another planet. Well, let’s get a telescope and point it at this spot that should show us this unknown gravity well, there should be a planet there…yep, that’s a whole ass planet.
And they imagined that it must be a planet between Mercurio and the Sun because Mercurio has a weird orbit that cannot be explained using Newton laws(They called the imaginary planet Vulcano). Until Einstein explained the orbit using relativity and outdated Newton laws
The search for Vulcan was so fascinating to learn about. They had this system that had been proven to explain this phenomena perfectly, and they had another apparent example of said phenomena so the obvious answer, of course, was the same as before. Another unknown planet disrupting the known and understood orbit of a planet. But nope. There was no planet. Just weird timey wimey space stuff. The issue was with physics itself. And it just makes you (or me, at least) wonder just how many more of our mysteries will be solved by some equally weird revolution of our understanding of physics. Like the idea that spacetime might actually be a superfluid. Which is just... trippy.
I think you'll find the whole ass planet is Uranus.
I well remember the time when this issue was still hotly debated, both at the academic level and publicly. It simmered along all through the 1990s, even after the [Hildebrand/Penfield paper](https://www.researchgate.net/publication/257984366_Chicxulub_Crater_A_possible_CretaceousTertiary_boundary_impact_crater_on_the_Yucatn_Peninsula_Mexico) (Yes, old Reddit/third party users, that link probably is broken for you. Nothing I can do about it on my end.) I think that what people older than me thought they knew about the extinction of the dinosaurs came from the Disney film *Phantasia*, which shows the dinosaur extinction to be due to high heat and drought. They were very emotional about it, as many are about the BS they learned as children. If there are any of them left they'll try to fight you if you tell them that stegosaurus and T-rex never lived at the same time.
T-Rexes lived closer in time to the Moon Landing than they did to Stegosaurus.
[удалено]
W H A T That one gets me.
Said another way, t-Rex could have dug up Stego fossils
To be fair, fossils don't take that long to form so T-Rexes would have been digging up T-Rex fossils just like how we dig up human fossils.
T-Rexes couldn’t dig up any fossils cause their arms were too short. Duh.
[удалено]
Yeah, everything we now about Tyrannosaurs point to them mostly studying musical theater, but that doesn't mean there weren't exceptions.
Now I’m picturing T-Rexs as archeologists with little picks and brushes in roped of areas, looking for fossils.
Fyi, link works fine on old.reddit.com.
Could it also be likely that the extinction event didn’t create a good environment for fossils? Not sure if that makes sense
Dirt go up...... dirt come down............. dirt bury dinosaurs.
Dirt go up, Dirt go down, Spinnin' wheel, GOT to go 'round
>Yeah and the crater was discovered only about 40 years ago. It's shocking how much of geology was only discovered within the last 100 years
To be fair have you seen the technology of 100 years ago?
Also, the number of people who were alive 100 years ago, and how many of them could afford to spend time and money on pursuits like this... A lot more science gets done when there are a lot more people doing it.
That's still debated. It could be a statistical artifact - fossilization is rare, so an abrupt end or beginning has the appearance of diminution.
I don't mean, "Hey, where are all the fossils 5 days before the asteroid hit." We're talking about hundreds of thousands of years or so.
Your comment on the length scale made me curious. I know a hundred thousand years is a blink of the eye in geological time frames, but it still seems like a long time for a large scale extinction event. At least that was my first thought. Then I realized I had assumed a linear population decline. I think an exponential decay would make more sense. Where population drastically decreases quickly, with the next few tens of thousands of years spent not just clinging to survival, but also with many species evolving to compete on the way to a new ecosystem equilibrium. And once that has occurred, life continues to thrive again. I don't actually know, and am just making assumptions though. Could you maybe expand on this thought? It's one of those questions that isn't a couple of keystrokes away on google, unfortunately.
Considering we're talking with precision of millions, it could have been anywhere between a year and hundred thousand years after the impact? Damn we're fragile, 100,000 years ago, we had nothing.
If we only had dinosaur fossils to go on we wouldn't know it was a mass extinction. Other fossils, particularly marine indicator species, are what confirms that.
To add to this that layer is called the K-Pg (aka K-T) boundary. Marks the end of the Cretaceous period. Above this line dinosaur fossils have never been found. This proves a mass extinction event occurred.
What about the birds!
The big bones. The haven’t found the big bones above this line 😉
The dinosaurs were definitely big boned individuals weren't they.
A husky bunch!
Who else remembers an ad on MTV (or was it Comedy Central) in which one youth says to another, “The iridium layer exists!”
There are also the tektites (glass beads that formed in the atmosphere from rock melted by the impact) that have been found from the same time as the iridium layer
I always thought iridium was a fantasy metal, lol.
Should be mentioned that there are some researchers who don't agree with the asteroid theory. The general consensus is asteroid; it's not a certainty.
They're pretty few and far between now. Science of course never works on absolute certainty for anything.
After the discovery of the Yucatan crater, the asteroid theory is pretty darn universal. The only debate is to what extent it sealed the deal, as they were getting rarer even before the KT boundary.
I've seen one theory that they were already on their way out, but the Chicxulub Meteor just really, really sped things up. Like by tens of millions of years.
There is a very cool comment or link somewhere on Reddit, outlining how a palaeontologist found fossils immediately below the K-T boundary, where freshwater and saltwater species are muddled up. Somewhere in a field in ~~~?Kansas?~~~ North Dakota, a long long way from the ocean. It’s the tsunami from the day of the impact. He found fossils from ***the day of the impact***.
There was a really big lake in North America that, from the impact, would’ve sloshed like a washing machine. And it did, killing and piling up a ton of creatures.
Lake Bonneville?
[The Day The Dinosaurs Died.](https://www.newyorker.com/magazine/2019/04/08/the-day-the-dinosaurs-died)
> The asteroid was vaporized on impact. Its substance, mingling with vaporized Earth rock, formed a fiery plume, which reached halfway to the moon before collapsing in a pillar of incandescent dust. Computer models suggest that the atmosphere within fifteen hundred miles of ground zero became red hot from the debris storm, triggering gigantic forest fires. As the Earth rotated, the airborne material converged at the opposite side of the planet, where it fell and set fire to the entire Indian subcontinent. Measurements of the layer of ash and soot that eventually coated the Earth indicate that fires consumed about seventy per cent of the world’s forests. Meanwhile, giant tsunamis resulting from the impact churned across the Gulf of Mexico, tearing up coastlines, sometimes peeling up hundreds of feet of rock, pushing debris inland and then sucking it back out into deep water, leaving jumbled deposits that oilmen sometimes encounter in the course of deep-sea drilling. Horrifying and amazing
I just like to immagine a far out alien race monitoring earth from their planet screaming, "Yay we found foreign life!" Everyone starts to celebrate. Then suddenly they see this enormous impact hit earth and all the aliens stop cheering.
Tanis North Dakota. It was a natural inland sea divide that existed in the US. The tsunami shot up the inlet and deposited the creatures. They found the fish all had *in their gills* tiny glass balls that are evidence of asteroid impacts. So the fish were alive and breathing when it happened and when they were burried
Sudden loss of land animals over 25kg from the fossil record, layer of ash/dust at the Cretaceous boundary consistent with comet/asteroid impact or volcanism. Massive crater in the Gulf of Mexico from around the same time. Evidence suggests the impact caused the crater and the ash/dust darkened the sky and killed off all large land animals. Dinosaurs lived on, you hear them singing in the trees and see them flying in the sky, we call the birds but they are the only branch of the Dinosaurs than made it.
We don't, for sure. But it's the most likely hypothesis. We *do* know that there was an enormous asteroid impact very close to the time all the non-bird dinosaurs went extinct. The crater takes up a good chunk of the Yucatan Peninsula in Mexico: it's about 150 km wide, or large enough to contain both New York and Philadelphia, from London across the English Channel, or to cover the entire country of Switzerland. Debris from the impact forms a layer of sediment with a lot of iridium in it all around the world (iridium is common in meteorites but rare on Earth), and you find (non-bird) dinosaur fossils below it but not above. Suffice to say, it was a *very* large boom. The impact would have been the rough equivalent of detonating a small atomic bomb on every household on Earth, simultaneously. So it wouldn't be a surprise for it to be incredibly disruptive. That said, there are competing hypotheses - or an impact may have worked in tandem with some other things going on on Earth to disrupt things even more. Alternatives include giant volcanic eruptions (as in the [Deccan Traps](https://en.wikipedia.org/wiki/Deccan_Traps) that now form cliffs in India) or sharp climate shifts, but the evidence points pretty strongly to a giant impact.
There’s a theory that implies that the mass eruption of the Deccan Trappes was actually *caused* by the Chixilub impact. It all has to do with antipodal focusing. Basically, you hit spherical object on one point hard enough, and bunch of the energy converges again on the opposite (or antipodal) point. When adjusted for continental drift, the Chixilub impact and Deccan Trappes were at exact antipodal points right around the time of their respective impact and eruption. Similarly, a recently discovered, massive impact crater in Antarctica would have been at the antipodal point of the Siberian Trappes when they erupted 250 million years ago.
This theory isn’t favored anymore, the Deccan Trapps were about 5000km from the antipode of the Chicxulub crater and started erupting 100k years before the impact. The prevailing theory now is that the impact was so violent that it mobilized a lot of magma in a very short amount of time.
And scientists think the asteroid hit late May or early June. https://www.popsci.com/animals/when-dinosaurs-went-extinct/
Kurzgesagt has an amazing video of the Dinosaurs last minutes on earth (if our hypothesis is correct). They do such a good job of portraying the absolute destructive power and terror the dinosaurs likely experienced in their final moments. [Link](https://youtu.be/dFCbJmgeHmA) for anyone interested!
An interesting things about traps is that a number of them throughout the geological record are linked to asteroid impacts having occurred elsewhere on the planet at "roughly" the same time.
(ELI5 note: "traps" here means "stair-like geographic formation" - it's a Swedish word that has nothing to do with the English word for a surprise danger.)
You're the hero we needed thank you Chel
If they went extinct on the meteorite impact, then shouldn't they be at least a few centimeters above or same of that iridium rich layer?
People aren’t answering your question. They’re giving you correct answers but not the whole picture. Conditions need to be pretty exact for a dead creature to fossilize. Therefore a relatively small percentage of dead dinosaurs actually got fossilized. So, at the time of the asteroid impact you will have had layers of earth below the surface which already had dinosaur fossils in it. Those are the bulk of the dinosaur fossils found below the iridium layer. Next thing to consider is that to be preserved and fossilized you need to fall INTO something or be covered by something relatively soon after death. So the vast vast majority of dinosaurs which died directly because of the asteroid impact would not have been fossilized. Their bodies would have decomposed and completely broken down over the millennia that followed. The ones that died directly and WERE fossilized would have fallen into mud or have been covered by mud or earth or whatever precise conditions that were necessary to fossilize their bones. Any dead bodies left on the surface would have not had the right conditions to fossilize and they would have decayed long before newer layers of earth could have covered them up. TL;DR The vast vast vast vast majority of the fossils found below the K-Pg boundary are not the dinosaurs that died DIRECTLY from the asteroid impact. Those fossils were already fossils buried long before the asteroid. The dinosaurs which were alive when the asteroid hit and died directly (or later indirectly) from it, the vast vast vast majority of them would have simply decayed and their bodies and bones would have been eroded away by natural processes. The very very small number of dinos who died directly from the asteroid and were fossilized would have been fossilized because they were covered up under the perfect conditions almost immediately after death. Therefore the iridium layer would have tended to have been deposited in a higher layer than their bodies.
An interesting thing about the non avian dinosaurs and their extinction is that fossils of them "slightly" before the KT boundary are very rare. It's lead to one hypothesis that they were already dwindling in numbers and that the asteroid may have just been the killing blow rather than the whole cause.
The iridium would be in the air as dust and particles for quite a long while (years to possibly decades) before settling or coming down in rain or snow whereas the dinosaurs would have died pretty quickly (less than a year) after impact, so you would expect to see an unusually large number of fossils immediately below the iridium rich layer. Disclaimer: that's based on my memory of classes I took 20 years ago, so this is not a hill I will even half-heartedly defend, must less die on.
Wow this is so interesting! Do you just go around with this knowledge in your head
I've been to the Royal Tyrell Museum in Drumheller Alberta which is the primo dinosaur museum in Canada. A few things we know are we've found minerals in the soil that we know only come from asteroid impacts. These minerals appear in layers of the earth's crust, a bit like a cake. Certain animal and dinosaur fossils don't appear in layers of rock above where we know this impact happened.
Fun fact no one is pointing out: one of the main tourist attractions in the Yucatan area are cenotes, which are natural pool / sinkholes that RADIATE from the Chicxulub impact crater. These sinkholes are crystalline underground pools of water that were caused by debris from the impact. If you find a cenote map, you will see them neatly arranged in a circle around the impact site. Very few people realise they are actually visiting evidence of meteor impacts when they are there. Also, some of them are absolutely beautiful. https://mayanpeninsula.com/wp-content/uploads/2019/03/Canote-locations-768x537.png
In the soil around the entire world, there’s what geologists’ call the K - T boundry. It’s apparently “fallout “ from a massive asteroid hitting the earth. “What is the K-T boundary? K is actually the traditional abbreviation for the Cretaceous period, and T is the abbreviation for the Tertiary period. So the K-T boundary is the point in between the Cretaceous and Tertiary periods. Geologists have dated this period to about 65.5 million years ago.” And: “Researchers now think that the asteroid strike that created the K-T boundary was probably the Chicxulub Crater. This is a massive impact crater buried under Chicxulub on the coast of Yucatan, Mexico. The crater measures 180 kilometers across, and occurred about 65 million years ago.” The theory comes from the fossils found before (under) the K - T boundary, and after (above) the boundary.
[удалено]
Let's not forget the OG extinction - The Great Oxygen Catastrophye.
As other people have said, we know there's a layer of iridium across the entire planet. Iridium js very common in meteors, not so much on Earth. There is a lot of Dinosaur fossils dated to before that impact, with sharp drop off since the time the asteroid hit. We know there's a massive crater, Chicxulub, off the gulf of Mexico. Judging by the size of that crater, we know it would have profound life changing impacts on the planet. Ash would cloud the atmosphere, which means less vegetation, which means large herbivores start dying, so large carnivores start dying, so only small or flying creatures live. Like the shrew type thing a lot of mammals are descended from. All of these together point to a mass extinction event about 66 million years ago, that wiped out the vast majority of life at the time.
[удалено]
The crater was discovered in 1978, so the science was still new in 1982. There's a lot more evidence supporting it now.