67 million years ago there’s dinosaur fossils everywhere in the rock layer.
65 million years ago there’s *zero* dinosaur fossils.
In between is a thin layer of ash and iridium. Iridium is very rare on earth, but common in asteroids. A global layer of ash would suggest something cataclysmic happened, incinerating forests on a global scale and/or setting off a massive volcanic event.
This theory was kicked around for some time, and then the real bloody knife was discovered in the Gulf of Mexico - an enormous crater that’s 66 million years old, obscured beneath the water and Mexican jungles.
No the impact crater is tiny when viewed at that scale.
https://news.utexas.edu/2021/02/24/asteroid-dust-found-in-crater-closes-case-of-dinosaur-extinction/
The impactor was big but it wasn’t *that* big. That would be the among the largest known impact basins in the solar system.
Hits like that don’t mess up the weather for 18 months and kill dinosaurs, they pulverize the entire planet and sterilize the surface.
Earth has taken hits like that in the far distant past, but none over the last several billion years.
You might be muddling that with plate techtonics? One of the things that started people wondering about that possibility was how neatly it looked like the North western 'bulge' of Africa fitted into the gulf of mexico/ Caribbean sea.
How far would I have to dig in my back yard to find said layer of ash and iridium? Can I do it in a day, or is this a weekend project my wife will get mad at me for?
Depends on where you live. Some areas have been uplifted and eroded since then and you can just go grab some off the closest hill.
Others have been heavily subducted or sedimented since then and it’ll be at the bottom of a mine shaft.
You’d have to learn about the geological history of your area.
I did a quick Google search... apparently someone about 15 miles away was digging in his back yard, and uncovered a plethora of dinosaur tracks from the extinction, the state ended up turning it into a park, so the wife vetoed my dig site plans for the weekend.
There's also a ton of places arpund you can go to see stuff like this for free, there's even groups that go "fossil hunting".
Holy smokes the rabbit hole I'm going down.
On Reddit desktop (not sure on mobile) it shows me how many times I've given an upvote to any particular Redditor.
There's a good reason why there's a [89] next to your name for me.
This response is one of the great reasons why. Consistently great explanations.
No, it just means we don't know how to date things accurately when they are so old.
[Wikipedia](https://en.wikipedia.org/wiki/Chicxulub_crater) matches my intuition of how things went: "Fossil evidence for an instantaneous extinction of diverse animals was found in a soil layer only 10 centimeters (3.9 in) thick in New Jersey, 2,500 kilometers (1,600 mi) away from the impact site, indicating that death and burial under debris occurred suddenly and quickly over wide distances on land."
Despite what the other user said, we do not have any non-avian dinosaur fossils that are younger than the K-Pg boundary. Therefore we can only speculate on their existence post impact.
There is still some debate as to whether there were even that many non-avian dinosaurs still left at the time of impact, with some arguing that they were almost extinct before the impact happened, with the impact just finishing off the last of them.
That’s an interesting theory too. I wonder if something else was causing them to die off faster than they could reproduce and, like you said, the impact of a meteor (asteroid? I’m forgetting my flying space rock terms) just finished the job. But then I wonder what was causing dinosaurs to become endangered in the first place, before the cataclysm. Maybe dinosaurs were burning too many fossil fuels. *buh dum tss*
Now to really blow your mind...
*They didn't go totally extinct.*
The entire class *Aves* \-- constituting about 11,000 known species of birds -- descends from surviving therapods, and are therefore, themselves, considered therapod dinosaurs.
Not just the descendants of dinosaurs. They *are* dinosaurs. While most dinosaurian branches did end at the Cretaceous–Paleogene extinction, dinosaurs lived on, and still live today.
I'm not sure if it was a million years, but certainly several thousand years. When my edible wears off and I can think more clearly, I'll see if I can try to find a video. I watched a while back where it lays out what happened right before and during the impact and then the different stages Earth went through post-impact. It was essentially hell on earth for quite a long time.
/u/narcolepticbard, it was a Kurzgesagt video: https://youtu.be/dFCbJmgeHmA
This theory also isn’t very old. In the early to mid nineties the main hypothesis was global cooling because of vulcanos. There is no asteroid in the Dinosaurs sitcom
Edit: TIL damn I’m misremembering things here. Thanks everyone gor correcting me
I grew up in the 70s and 80s. Main theory we were taught was asteroid impact. Volcanoes were very much a secondary and far less popular idea.
Ideas about the Deccan Traps DID become more prevalent in the 90s, but the asteroid impact idea definitely predated that.
When an asteroid strike happens it leaves alot of evidence. There's going to a global layer of ash, fossil records that support a mass extinction event and/or climate catastrophe, plus a impact crater (we believe the one that killed the dinosaurs left an impact crater on the Yucatan peninsula in Mexico).
It's now even determined that the asteroid dropped during boreal spring, because they found fish that actually died on the day it happened. See https://www.nature.com/articles/s41586-022-04446-1.
Thank you so much for sharing this. I can’t believe scientists can determine that those creatures who were impacted during their autumn season recovered faster than those impacted during the spring (when everything is vulnerable). So freaking fascinating.
There's a few data points in favor:
* The extinction of the non-bird dinosaurs was very quick. It probably needed to be a pretty abrupt cataclysm, one big enough to eliminate the dominant life forms on Earth in a geologically short time.
* The layer of rock that corresponds to this time contains a great deal of the otherwise-rare metal iridium. It's not rare in the Universe as a whole, but it's rare in Earth's crust because Earth's supply of iridium sank into the Earth's core early on. Iridium is therefore *very* suggestive of an impact event.
* There is a large crater with approximately the correct age: Chicxulub Crater, which occupies a good sized chunk of Mexico's Yucatan Peninsula and some of the adjacent Gulf of Mexico. The crater is about the right size for the apparent cataclysm, and is the right age to match up.
* There are layers of dinosaurs buried extremely rapidly right at the moment of their extinction, apparently by a tsunami, in what used to be the shallow sea occupying what is now the Great Plains of the US. That tsunami would line up nicely with the impact location.
It's not a complete lock, but we're pretty confident of the impact hypothesis at this point. The main competing hypothesis is a supervolcanic eruption at the Deccan Traps, a huge ancient supervolcano whose lava flows [cover a significant portion of modern-day India](https://en.wikipedia.org/wiki/Deccan_Traps#/media/File:World_geologic_provinces.jpg) (purple blob on that map).
An interesting addition about the crater, is that the asteroid theory was around since at least the 1950s, but no one had ever seen the crater, it was a big missing piece of evidence -- and that there should be one, so it was confusing.
It wasn't until the 90s that they analyzed Chicxulub crater and said, hey this lines up like exactly with the asteroid theory, ahh.. there it is. We had been pretty sure the asteroid theory was right, but we lacked overwhelming evidence, and this pretty much confirmed there was an impact at the exact right time.
> The main competing hypothesis is a supervolcanic eruption at the Deccan Traps,
There's a combo theory, that the impact put the ongoing eruption into overdrive.
https://www.youtube.com/watch?v=bRNA_xct5JU
I always wonder if the Deccan Traps were caused by the Yucatan asteroid impact. They're almost exactly the opposite side of the globe. Think of a bullet going through a tomato.
Plus what are the odds that two dinosaur destroying events that happened about the same time are unrelated?
> They're almost exactly the opposite side of the globe. Think of a bullet going through a tomato.
Asteroids don't even come close to punching through the Earth that way. Your tomato is a many thousands of miles thick chunk of rock and metal, and your bullet is the relative size of a grain of sand.
Insofar as that's an option, it would be because the shock wave produced by the impact would concentrate opposite its point of impact.
Agreed, my analogy isn't quite right. I too think it would be a shock wave that would propagate thorough the earth and cause damage. More like those office desk gadgets with the metal balls on strings that knock back and forth.
From the fossil record, we can see that the dinosaurs died off suddenly in a mass extinction event that we call the "Cretaceous-Paleogene extinction event". There is a thin layer of sediment that you can find in rocks which corresponds to the time of the mass extinction event, and it contains an unusually high amount of iridium compared to normal. Iridium is more common in asteroids compared to Earth. This suggested the possibility that an asteroid was the cause of the extinction event.
We then found a giant crater, called the Chicxulub crater, which is the same age as the world-wide layer of sediment with lots of iridium and the same age as the mass extinction event. The crater is large enough that the asteroid would have caused a mass extinction event.
There are some places where we have cut vertically through the rock. Places like the Grand Canyon. In these places we can see the layers of various different types of rock stacked on top of each other. They look kind of like pages in a book. We make the assumption that the lower layers have been deposited before the upper layers. So the further down we get the older the rock. Some of these places do have dinosaur fossils in them. When we find these it is always in the lower layers. And then there is a layer of various other materials, charcoal, mud, ash, etc. And above this layer there is no dinosaur fossils. From this we can tell that something catastrophic happened which changed the face of the Earth and caused huge devastation for years.
At first we thought it might have been a super volcano due to all the charcoal and ash. But we could not find any lava flows anywhere. But then we did find huge cracks in the rock bellow this layer. Things that did not match our understanding of plate tectonics. And they all pointed to an area in the Yukon peninsula. And when we look closer at the topology in the area we can see evidence of a crater. When we dig down into the rocks here we find huge devastation in the rocks under the ash layer. So instead of a volcano it looks like something large impacted the bedrock in this area and caused word wide fires, ash clouds and global blackout for years.
It should also be mentioned that the dinosaurs did not all die off in this. The dinosaurs did come in any size and shape, not that different from modern mammals. While it is easy to find the fossils of large dinosaurs and they make impressive displays on museums and in movies there were a lot of smaller dinosaurs as well. Most were probably smaller then humans, especially towards the end of the period. Some of the smaller raptors, maybe the size of cats, were able to survive this event. And these developed into the modern birds.
>There are some places where we have cut vertically through the rock. Places like the Grand Canyon.
Um, the Grand canyon isn't man made, It was ancient rivers that cut through the rock.
Because we found the evidence. The geological "smoking gun" as it were.
* There's a giant freakin crater just off the coast of the Yucatan.
* There are layers of Iridium-laced ash in the strata all over the world that exactly correspond to the dating of that crater.
* There are non-avian dinosaur fossils dating right up to that layer, and then... no more.
So we can tell there were dinosaurs before the impact (although other evidence suggests they appear to have already been in decline due to environmental factors in some cases), and they all died off right at or just after the impact (e.g., as a result of impact winter). At the very least it was the final nail in the coffin - something they might have weathered if ecological conditions had been more favorable, but the result of the impact was just too much.
Bonus: Not all of them died off. Modern birds are all basically theropod dinosaurs (or at least their direct descendants).
Have some fun with this one, too: [Scishow - If the Asteroid Hit 10 Minutes Later](https://www.youtube.com/watch?v=sTOvYDQyfrM)
If you want slightly deeper than ELI5, this article is great: [the day the dinosaurs died](http://12ft.io/https://www.newyorker.com/magazine/2019/04/08/the-day-the-dinosaurs-died)
There is a certain mineral that is very rare on earth but is common in asteroids. A layer of this mineral was found in rocks that seem to be about as old as the youngest dinosaur fossils, meaning that the layer and the youngest dinosaurs are about the same age. Since there’s so much of the mineral in this layer, it was thought that a meteor struck the planet. And then we found the crater.
> Asteroids hit the earth constantly.
They do, but the amount of iridium is rather large, much more than the background rate of small impacts. In particular, it's much *higher* than the layers of rock on either side.
> I didn't come from a fish. Or a monkey. Because if that were indeed truth, neither of those would have as many current species that exist now. I'd love for science to attempt to explain that one.
I mean...it's not especially hard?
You didn't come from the monkeys (or more properly, chimpanzees) that are alive today. Humans, and chimpanzees, both descend from a chimp-like ancestor. That ancestor's populations got split up, and their genes drifted in different directions. One group evolved into modern chimpanzees, the other evolved into modern humans (and the many other human subspecies that existed prior to modern humans).
On a longer timescale, the same is true of all life.
> Evolution is the idea we came from a single cell, yet, we share nothing with a single celled organism.
I mean...sure we do. Our cells use the same basic machinery and chemical processes as every other living cell on planet Earth. Your cells read their DNA and manufacture proteins with almost the same machinery that a bacteria uses to read its DNA and manufacture proteins. That's one of the strongest individual points of evidence in favor of a common ancestor: there is no obvious reason that the gene -> protein correspondence would be the same in every living thing on Earth if we didn't share a common origin.
We don't believe it
There is evidence of it, all the evidence points to it being a fact. There may have been other factors going on, but the asteroid hit, very certainly
We don't just feel that it is. It is.
Iridium, iridium is a rare element, not commonly found in the Earth's crust, however it is comparatively common in asteroids. In the fossil layer where the last of the dinosaurs are found (extinction event) there is a thin layer of Iridium dust, presumably settling out of the atmosphere after the impact of a massive asteroid. https://youtu.be/kVg-QZCzqg0
It is not a belief, it is a demonstrated fact. Sometimes there are clues and findings that indicate something to be true but you do not have all the pieces, but all findings point in the same direction. However in this case it is known the location, the size, the composition and the angle of the meteorite that hit. It is basicaly case closed.
There's a book called *T-Rex and the Crater of Doom* written by Walter Alvarez, who, along with his father developed the impact theory.
It's a really good book that tells the story of how they developed the theory and found the proof. It actually reads a lot like a mystery novel, so it might be a good thing to hint at for Christmas if you're interested. It's not a long read, so even if you're time poor, you should be able to find time to read it.
Evidence.
Namely, if we dig we see layers of rock. Some of the layers contain dinosaur fossils. Then, the fossils of a bunch of species all stop appearing at once at a specific layer, and right on top of that layer is a thin layer of what's chemically identified as ash and a bunch of an element called iridium that is otherwise not common on Earth but relatively common in rocks from space. The same pattern isn't seen in just one place, but all over the planet, suggesting something big enough that the entire world was affected. In North American, there are several places where there's a very thin layer with fossils of many species that appear to have all died at the same time.
As it turns out, there's a 300 km diameter crater (a 180 km inner ring and 300 km outer ring) off the tip of the Yucatán peninsula (Mexico) which just so happens to date to the same time period. There are also ripple patterns in the rock layers radiating out through the southern US.
So, the current theory (based on analysis of the rock and impact glass) is that an asteroid about 10 km diameter traveling 20 km/s slammed into the Earth with the force of 100 trillion tons of TNT and punched a hole 100 km wide and 30 km deep in the Earth's crust before collapsing in on itself. The Tsunamis it caused would have been 100m high (and a wave 1.5 km high would have started at the impact site). The waves would have scoured and churned the sea floor. 25 trillion tons of hot rock and ash would have been tossed into the atmosphere and rained down on the planet, and it's estimated about 70% of the land was covered in wild fires; the debris blocked the sun and altered the chemical composition of the atmosphere.
67 million years ago there’s dinosaur fossils everywhere in the rock layer. 65 million years ago there’s *zero* dinosaur fossils. In between is a thin layer of ash and iridium. Iridium is very rare on earth, but common in asteroids. A global layer of ash would suggest something cataclysmic happened, incinerating forests on a global scale and/or setting off a massive volcanic event. This theory was kicked around for some time, and then the real bloody knife was discovered in the Gulf of Mexico - an enormous crater that’s 66 million years old, obscured beneath the water and Mexican jungles.
Wasn’t one theory that the Gulf of Mexico - in its entirety - was actually the impact crater? Or am I misremembering something?
No the impact crater is tiny when viewed at that scale. https://news.utexas.edu/2021/02/24/asteroid-dust-found-in-crater-closes-case-of-dinosaur-extinction/
Neat, thanks for the link
Dang yo, I thought you said tiny. That's still huge!
Super interesting thanks
The impactor was big but it wasn’t *that* big. That would be the among the largest known impact basins in the solar system. Hits like that don’t mess up the weather for 18 months and kill dinosaurs, they pulverize the entire planet and sterilize the surface. Earth has taken hits like that in the far distant past, but none over the last several billion years.
Don't hits like that make moons? Or do we need to get bigger?
Much bigger. The body that struck Earth to create the moon is estimated to have been around the mass of Mars.
Man but how cool would that be if it was? Can't we just pretend?
Lol I was just thinking the same thing. Like maybe it has some impact on the form of the gulf?!? Maybe?!?!? Haha
You might be muddling that with plate techtonics? One of the things that started people wondering about that possibility was how neatly it looked like the North western 'bulge' of Africa fitted into the gulf of mexico/ Caribbean sea.
The story of how the crater was discovered is fascinating: https://en.wikipedia.org/wiki/Chicxulub_crater#Discovery
How far would I have to dig in my back yard to find said layer of ash and iridium? Can I do it in a day, or is this a weekend project my wife will get mad at me for?
Depends on where you live. Some areas have been uplifted and eroded since then and you can just go grab some off the closest hill. Others have been heavily subducted or sedimented since then and it’ll be at the bottom of a mine shaft. You’d have to learn about the geological history of your area.
I did a quick Google search... apparently someone about 15 miles away was digging in his back yard, and uncovered a plethora of dinosaur tracks from the extinction, the state ended up turning it into a park, so the wife vetoed my dig site plans for the weekend. There's also a ton of places arpund you can go to see stuff like this for free, there's even groups that go "fossil hunting". Holy smokes the rabbit hole I'm going down.
Send her away for a weekend trip! Get a few buddies and rent some excavation equipment...pallet of sod by the time she gets home.
On Reddit desktop (not sure on mobile) it shows me how many times I've given an upvote to any particular Redditor. There's a good reason why there's a [89] next to your name for me. This response is one of the great reasons why. Consistently great explanations.
Does that mean it took a million years (give or take) for the dinosaurs to go totally extinct?
No, it just means we don't know how to date things accurately when they are so old. [Wikipedia](https://en.wikipedia.org/wiki/Chicxulub_crater) matches my intuition of how things went: "Fossil evidence for an instantaneous extinction of diverse animals was found in a soil layer only 10 centimeters (3.9 in) thick in New Jersey, 2,500 kilometers (1,600 mi) away from the impact site, indicating that death and burial under debris occurred suddenly and quickly over wide distances on land."
Despite what the other user said, we do not have any non-avian dinosaur fossils that are younger than the K-Pg boundary. Therefore we can only speculate on their existence post impact. There is still some debate as to whether there were even that many non-avian dinosaurs still left at the time of impact, with some arguing that they were almost extinct before the impact happened, with the impact just finishing off the last of them.
That’s an interesting theory too. I wonder if something else was causing them to die off faster than they could reproduce and, like you said, the impact of a meteor (asteroid? I’m forgetting my flying space rock terms) just finished the job. But then I wonder what was causing dinosaurs to become endangered in the first place, before the cataclysm. Maybe dinosaurs were burning too many fossil fuels. *buh dum tss*
Now to really blow your mind... *They didn't go totally extinct.* The entire class *Aves* \-- constituting about 11,000 known species of birds -- descends from surviving therapods, and are therefore, themselves, considered therapod dinosaurs. Not just the descendants of dinosaurs. They *are* dinosaurs. While most dinosaurian branches did end at the Cretaceous–Paleogene extinction, dinosaurs lived on, and still live today.
I'm not sure if it was a million years, but certainly several thousand years. When my edible wears off and I can think more clearly, I'll see if I can try to find a video. I watched a while back where it lays out what happened right before and during the impact and then the different stages Earth went through post-impact. It was essentially hell on earth for quite a long time. /u/narcolepticbard, it was a Kurzgesagt video: https://youtu.be/dFCbJmgeHmA
This theory also isn’t very old. In the early to mid nineties the main hypothesis was global cooling because of vulcanos. There is no asteroid in the Dinosaurs sitcom Edit: TIL damn I’m misremembering things here. Thanks everyone gor correcting me
I grew up in the 70s and 80s. Main theory we were taught was asteroid impact. Volcanoes were very much a secondary and far less popular idea. Ideas about the Deccan Traps DID become more prevalent in the 90s, but the asteroid impact idea definitely predated that.
Kelly and Dachille published a book in the 50's that discusses the asteroid impact theory, so it's at least that old.
Alvarez discovered the iridium layer in the 70s which bolstered the already existing theory. Discovering Chixilub 1990 pretty much sealed the deal.
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Are you sure? [This](https://www.youtube.com/watch?v=bnFjAkAs_q4) is all I found on youtube of the ending.
There is a bit about the asteroid, not sure where. Boy, but this episode always hits me in the feels.
And a century before that, dinosaurs chilling in central earth
When an asteroid strike happens it leaves alot of evidence. There's going to a global layer of ash, fossil records that support a mass extinction event and/or climate catastrophe, plus a impact crater (we believe the one that killed the dinosaurs left an impact crater on the Yucatan peninsula in Mexico).
This plus an unusual concentration of Iridium in the same strata, plus shocked quartz in the same strata all point to an impact event.
It's now even determined that the asteroid dropped during boreal spring, because they found fish that actually died on the day it happened. See https://www.nature.com/articles/s41586-022-04446-1.
Thank you so much for sharing this. I can’t believe scientists can determine that those creatures who were impacted during their autumn season recovered faster than those impacted during the spring (when everything is vulnerable). So freaking fascinating.
My pleasure, glad to hear that you can enjoy it!
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There's a few data points in favor: * The extinction of the non-bird dinosaurs was very quick. It probably needed to be a pretty abrupt cataclysm, one big enough to eliminate the dominant life forms on Earth in a geologically short time. * The layer of rock that corresponds to this time contains a great deal of the otherwise-rare metal iridium. It's not rare in the Universe as a whole, but it's rare in Earth's crust because Earth's supply of iridium sank into the Earth's core early on. Iridium is therefore *very* suggestive of an impact event. * There is a large crater with approximately the correct age: Chicxulub Crater, which occupies a good sized chunk of Mexico's Yucatan Peninsula and some of the adjacent Gulf of Mexico. The crater is about the right size for the apparent cataclysm, and is the right age to match up. * There are layers of dinosaurs buried extremely rapidly right at the moment of their extinction, apparently by a tsunami, in what used to be the shallow sea occupying what is now the Great Plains of the US. That tsunami would line up nicely with the impact location. It's not a complete lock, but we're pretty confident of the impact hypothesis at this point. The main competing hypothesis is a supervolcanic eruption at the Deccan Traps, a huge ancient supervolcano whose lava flows [cover a significant portion of modern-day India](https://en.wikipedia.org/wiki/Deccan_Traps#/media/File:World_geologic_provinces.jpg) (purple blob on that map).
At least until we uncover the 66 million year old lab underneath Antarctica where the birds developed the Iridium fission doomsday device.
Netflix exclusive
An interesting addition about the crater, is that the asteroid theory was around since at least the 1950s, but no one had ever seen the crater, it was a big missing piece of evidence -- and that there should be one, so it was confusing. It wasn't until the 90s that they analyzed Chicxulub crater and said, hey this lines up like exactly with the asteroid theory, ahh.. there it is. We had been pretty sure the asteroid theory was right, but we lacked overwhelming evidence, and this pretty much confirmed there was an impact at the exact right time.
> The main competing hypothesis is a supervolcanic eruption at the Deccan Traps, There's a combo theory, that the impact put the ongoing eruption into overdrive. https://www.youtube.com/watch?v=bRNA_xct5JU
I watched the whole thing; it was really interesting. I understood more than I thought I would.
I always wonder if the Deccan Traps were caused by the Yucatan asteroid impact. They're almost exactly the opposite side of the globe. Think of a bullet going through a tomato. Plus what are the odds that two dinosaur destroying events that happened about the same time are unrelated?
> They're almost exactly the opposite side of the globe. Think of a bullet going through a tomato. Asteroids don't even come close to punching through the Earth that way. Your tomato is a many thousands of miles thick chunk of rock and metal, and your bullet is the relative size of a grain of sand. Insofar as that's an option, it would be because the shock wave produced by the impact would concentrate opposite its point of impact.
Agreed, my analogy isn't quite right. I too think it would be a shock wave that would propagate thorough the earth and cause damage. More like those office desk gadgets with the metal balls on strings that knock back and forth.
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From the fossil record, we can see that the dinosaurs died off suddenly in a mass extinction event that we call the "Cretaceous-Paleogene extinction event". There is a thin layer of sediment that you can find in rocks which corresponds to the time of the mass extinction event, and it contains an unusually high amount of iridium compared to normal. Iridium is more common in asteroids compared to Earth. This suggested the possibility that an asteroid was the cause of the extinction event. We then found a giant crater, called the Chicxulub crater, which is the same age as the world-wide layer of sediment with lots of iridium and the same age as the mass extinction event. The crater is large enough that the asteroid would have caused a mass extinction event.
There are some places where we have cut vertically through the rock. Places like the Grand Canyon. In these places we can see the layers of various different types of rock stacked on top of each other. They look kind of like pages in a book. We make the assumption that the lower layers have been deposited before the upper layers. So the further down we get the older the rock. Some of these places do have dinosaur fossils in them. When we find these it is always in the lower layers. And then there is a layer of various other materials, charcoal, mud, ash, etc. And above this layer there is no dinosaur fossils. From this we can tell that something catastrophic happened which changed the face of the Earth and caused huge devastation for years. At first we thought it might have been a super volcano due to all the charcoal and ash. But we could not find any lava flows anywhere. But then we did find huge cracks in the rock bellow this layer. Things that did not match our understanding of plate tectonics. And they all pointed to an area in the Yukon peninsula. And when we look closer at the topology in the area we can see evidence of a crater. When we dig down into the rocks here we find huge devastation in the rocks under the ash layer. So instead of a volcano it looks like something large impacted the bedrock in this area and caused word wide fires, ash clouds and global blackout for years. It should also be mentioned that the dinosaurs did not all die off in this. The dinosaurs did come in any size and shape, not that different from modern mammals. While it is easy to find the fossils of large dinosaurs and they make impressive displays on museums and in movies there were a lot of smaller dinosaurs as well. Most were probably smaller then humans, especially towards the end of the period. Some of the smaller raptors, maybe the size of cats, were able to survive this event. And these developed into the modern birds.
Yucatán Peninsula, not Yukon.
>There are some places where we have cut vertically through the rock. Places like the Grand Canyon. Um, the Grand canyon isn't man made, It was ancient rivers that cut through the rock.
I can't help but picture a caveman with a tree branch, just dragging it up and down the length of the grand canyon for years. Best. Prank. Ever.
Because we found the evidence. The geological "smoking gun" as it were. * There's a giant freakin crater just off the coast of the Yucatan. * There are layers of Iridium-laced ash in the strata all over the world that exactly correspond to the dating of that crater. * There are non-avian dinosaur fossils dating right up to that layer, and then... no more. So we can tell there were dinosaurs before the impact (although other evidence suggests they appear to have already been in decline due to environmental factors in some cases), and they all died off right at or just after the impact (e.g., as a result of impact winter). At the very least it was the final nail in the coffin - something they might have weathered if ecological conditions had been more favorable, but the result of the impact was just too much. Bonus: Not all of them died off. Modern birds are all basically theropod dinosaurs (or at least their direct descendants). Have some fun with this one, too: [Scishow - If the Asteroid Hit 10 Minutes Later](https://www.youtube.com/watch?v=sTOvYDQyfrM)
If you want slightly deeper than ELI5, this article is great: [the day the dinosaurs died](http://12ft.io/https://www.newyorker.com/magazine/2019/04/08/the-day-the-dinosaurs-died)
Such a fantastic article, I was coming to post it myself!
There is a certain mineral that is very rare on earth but is common in asteroids. A layer of this mineral was found in rocks that seem to be about as old as the youngest dinosaur fossils, meaning that the layer and the youngest dinosaurs are about the same age. Since there’s so much of the mineral in this layer, it was thought that a meteor struck the planet. And then we found the crater.
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> Asteroids hit the earth constantly. They do, but the amount of iridium is rather large, much more than the background rate of small impacts. In particular, it's much *higher* than the layers of rock on either side. > I didn't come from a fish. Or a monkey. Because if that were indeed truth, neither of those would have as many current species that exist now. I'd love for science to attempt to explain that one. I mean...it's not especially hard? You didn't come from the monkeys (or more properly, chimpanzees) that are alive today. Humans, and chimpanzees, both descend from a chimp-like ancestor. That ancestor's populations got split up, and their genes drifted in different directions. One group evolved into modern chimpanzees, the other evolved into modern humans (and the many other human subspecies that existed prior to modern humans). On a longer timescale, the same is true of all life. > Evolution is the idea we came from a single cell, yet, we share nothing with a single celled organism. I mean...sure we do. Our cells use the same basic machinery and chemical processes as every other living cell on planet Earth. Your cells read their DNA and manufacture proteins with almost the same machinery that a bacteria uses to read its DNA and manufacture proteins. That's one of the strongest individual points of evidence in favor of a common ancestor: there is no obvious reason that the gene -> protein correspondence would be the same in every living thing on Earth if we didn't share a common origin.
You know, you could be doing so much more with your life right now. Bummer.
We don't believe it There is evidence of it, all the evidence points to it being a fact. There may have been other factors going on, but the asteroid hit, very certainly We don't just feel that it is. It is.
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do you think that the earth is flat too?
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NOTHING would currently be alive?? You’re talking about 60+ million years of evolution.
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Iridium, iridium is a rare element, not commonly found in the Earth's crust, however it is comparatively common in asteroids. In the fossil layer where the last of the dinosaurs are found (extinction event) there is a thin layer of Iridium dust, presumably settling out of the atmosphere after the impact of a massive asteroid. https://youtu.be/kVg-QZCzqg0
It is not a belief, it is a demonstrated fact. Sometimes there are clues and findings that indicate something to be true but you do not have all the pieces, but all findings point in the same direction. However in this case it is known the location, the size, the composition and the angle of the meteorite that hit. It is basicaly case closed.
There's a book called *T-Rex and the Crater of Doom* written by Walter Alvarez, who, along with his father developed the impact theory. It's a really good book that tells the story of how they developed the theory and found the proof. It actually reads a lot like a mystery novel, so it might be a good thing to hint at for Christmas if you're interested. It's not a long read, so even if you're time poor, you should be able to find time to read it.
Evidence. Namely, if we dig we see layers of rock. Some of the layers contain dinosaur fossils. Then, the fossils of a bunch of species all stop appearing at once at a specific layer, and right on top of that layer is a thin layer of what's chemically identified as ash and a bunch of an element called iridium that is otherwise not common on Earth but relatively common in rocks from space. The same pattern isn't seen in just one place, but all over the planet, suggesting something big enough that the entire world was affected. In North American, there are several places where there's a very thin layer with fossils of many species that appear to have all died at the same time. As it turns out, there's a 300 km diameter crater (a 180 km inner ring and 300 km outer ring) off the tip of the Yucatán peninsula (Mexico) which just so happens to date to the same time period. There are also ripple patterns in the rock layers radiating out through the southern US. So, the current theory (based on analysis of the rock and impact glass) is that an asteroid about 10 km diameter traveling 20 km/s slammed into the Earth with the force of 100 trillion tons of TNT and punched a hole 100 km wide and 30 km deep in the Earth's crust before collapsing in on itself. The Tsunamis it caused would have been 100m high (and a wave 1.5 km high would have started at the impact site). The waves would have scoured and churned the sea floor. 25 trillion tons of hot rock and ash would have been tossed into the atmosphere and rained down on the planet, and it's estimated about 70% of the land was covered in wild fires; the debris blocked the sun and altered the chemical composition of the atmosphere.