The Day the Mesozoic Died: The Asteroid That Killed the Dinosaurs — HHMI BioInteractive Video

Imagine a world of giant reptiles, flying pterosaurs with wingspans of 40 feet, while beneath the waves, fierce predators called mosasaurs littered the seeds and

dinosaurs

roamed the earth for over a hundred million years, creatures like these ruled the planet. and then they were lost in the shadows. of time their extinction is a mystery for centuries this is all we have left of those magnificent creatures bones and from many of them we have collected enormous quantities of bones and from them we can say how these creatures lived what they looked like when they lived but we do not know why they disappeared.

Solving that mystery required some of the best scientific detective work of all time, and the trail began almost halfway around the world from here. This is Gubbio, a quiet Italian town. There is not a single giant reptile in sight, even in the past. It is everywhere you look, in the medieval palaces and churches, the houses and the narrow streets, while an even deeper past lies nearby, on the outskirts of Gubbio, Alessandro Mónito is searching for that distant past, he is a traveler in time moving towards the lost world of the

dinosaurs

, their ancient history. written on these limestone cliffs millions of years ago, these mountains were at the bottom of a deep sea collecting layers of sediment and being deposited slowly over time and eventually pushed by folding and uplifting tectonic forces, so all this rock and all these layers were once at the bottom of the ocean exactly and then all these other forces have brought this old rock to you yes, we can really study layer by layer like pages of a book the east of the earth the limestone of the deep Rubio marine now exposed next to El Camino became a magnet for scientists, especially this site that may seem ordinary but has one of the strangest features geologists face.

A thin layer of dark clay. In the 1970s, the clay caught the attention of an American geologist, Walter Alvarez, who was trying to determine. The relative ages of limestone layers by analyzing fossils left by small shelled sea creatures called foraminifera or fora for short, are among the most common ocean plankton. When they die, their shells become part of the sediment, as many species different ones have evolved over time. ages that can serve as markers of geological time, but as Álvarez stu

died

them, he noticed something surprising: what season puzzled him after the top of that white layer all these very diverse species of microfossils disappeared, so Sandra, when Walter Álvarez looked in these rocks saw all these foreign species, yes, and they are abundant, there are many species for thousands and thousands and thousands of years, but after this little vein of clay here along these layers of rock, those forums Those pieces are missing. have disappeared there is a band that is a fundamental mystery how what would make these small creatures disappear yes, so Álvarez was perplexed what this thin line of clay represented that was deposited 65 million years ago at the same time that the dinosaurs disappeared was there any bond?

The same questions were being asked 1,500 kilometers away, in Spain, on the Atlantic coast, outside the city of Zumaia, the Dutch geologist John Smith was studying the forums from a different ancient sea. Their fossilized shells form these limestone rocks that, like sticky mountains, once lay at the bottom. of the ocean now exposed, represent more than a million years of a geological period known as the Cretaceous. Like Alvarez in Italy, Schmitt had also found a strange layer of clay formed at the same time as telling a dramatic story. What can we tell about the history of the Earth?

Just by looking at these rocks, you can see at the end of one world and at the beginning of the next, there is a very sharp, extremely sharp dividing line between the two, that gray band that is that gray band that is there at the bottom. from those gray bones you see it's razor sharp and all this reddish brown rock the oceans are healthy and the steam is healthy they're stable they don't change at all and suddenly they get dramatic changes we call the KT boundary The KT boundary found in The bottom of this gray layer marks not only the end of a period, the Cretaceous, but also the Mesozoic era.

A much longer period of time, the history of animal life on Earth has been divided into three such segments: early life. Paleozoic, the era of dinosaurs or Mesozoic and the era of mammals or Cenozoic, the Cretaceous-Tertiary boundary lies right between these two eras marked here by this layer of clay that attracted it to this boundary. Well shown, we are seeing here in the same At the top of most of the Cretaceous rocks, these rocks are literally packed with foraminifera, that's why we call it Cretaceous and these rocks here are the Tertiary and the base of the Tertiary consists of a dark gray clay layer and there life has almost disappeared and the KT boundary is right in the middle, I can point it out, it is right here where we see a contrast between the purple and the dark, it is an extremely sharp boundary and just on the other side of that little thin line there is a big change in what you see on the forums and why is that like that?

Awesome to you, it's so amazing because there's no prior evidence of anything happening there, so it doesn't matter if I take a piece here, a piece of deer, or just below what we call the KT boundary, the ephra foramen will stay the same for They don't change overnight and then, bang, they disappear, so what does that tell you? It tells me that the base of the ocean food chain is gone and everything that depends on it is totally destroyed. right on the edge in Amsterdam? The change in the limit becomes clearer when Schmitt takes a closer look at the evidence in his laboratory, he analyzes four amps extracted from the limestone under the microscope.

The rich diversity of fossilized shells from the Cretaceous comes into focus. About four dozen species appear below the limit, but above it there is a different one. world these are the efra foremen from just below the limit and these are from just above the buyer only a few species have survived in the tertiary and they are much smaller as soon as you see the extinction and realize at the same time that the dinosaurs are disappearing, you know you are seeing something very important, but you see that no one has witnessed it, so we look for silent witnesses in the rock and the first thing that comes to mind is this beautiful game layer, a layer that varies in color and thickness and is found throughout the world Walter Álvarez also believed that he was a silent witness to the end of an era the key question was how long it took to form for the world to change to discover it he sought help at the University of California at Berkeley from a Nobel Prize winning physicist someone his father knew quite well Louie Alvarez Louie loved a good mystery no matter what field he was in and that's how physics joined geology in the quest to explain the extinction KT Alvarez looked at this layer tried To figure out how the time scale can be determined, he used his knowledge of astrophysics, his knowledge of nuclear physics, and realized that there is an element that is relatively rare in the Earth's crust and is found in meteorites.

The element was iridium, which steadily falls in an invisible shower of cosmic space dust if the lair had taken thousands of years to form. Alvarez thought there might be enough iridium to measure, but when the clay was analyzed, scientists were stunned to discover that it contained 30 times more iridium than the surrounding rock, plus the samples. from other KT sites had similar levels, too much to come from ordinary space dust, which could explain so much iridium deposited around the world, perhaps a catastrophic event in outer space. Alvarez wondered if a supernova exploding nearby could be responsible, so he asked me if that was possible.

I concluded that there was only a one in a billion chance of such a supernova occurring and that in about 100 million years ago the supernova would also have deposited a rare isotope plutonium-244, but tests revealed that there was none. I alternatively suggested that it could have been an

asteroid

or a comet. There are hundreds of

asteroid

s whose paths crossed the Earth's orbit. Their sizes vary from a few meters to hundreds of kilometers in diameter. So Louis Alvarez had this hypothesis that an asteroid or a comet. comet would cause this destruction he had the clue to the amount of According to this hypothesis, the iridium in Gubbio would spread around the world, so he could now calculate how much iridium had been deposited throughout the Earth.

Now you also know how much iridium is in asteroids and comets, so you can now calculate the size. Of the object, the answer was an asteroid ten kilometers in diameter, as big as Mount Everest and weighing hundreds of billions of tons. How could something that size wreak havoc on a large planet because traveling through the vacuum of space it would have crashed into the planet? The Earth's atmosphere at 80 thousand kilometers per hour 20 times faster than a bullet heating the air to several times the temperature of the Sun at the moment of impact the energy released would be equivalent to about 100 million nuclear bombs exploding at the same time an enormous mass of Pulverized debris would have been launched into space, part of it orbiting the Earth before raining down again.

The debris may have blocked the Sun for months. Photosynthesis would have stopped plants, herbivores, and then carnivores would have

died

. This was the asteroid impact hypothesis for how the Mesozoic era developed. It put an end to a big idea that was simply too big for some when Alvarez's hypothesis was first proposed; It was difficult for many scientists to accept it because for almost two centuries geologists had built their worldview around a gradual picture: a slow but steady change in the Earth without major changes. catastrophes were now hearing a proposal that something had come from outer space and rewritten the history of life in almost an instant Louie Alvarez became very frustrated when the paleontologist did not say yes sir thank you for solving our problem many of the paleontologists simply looked over it as someone who didn't know his field and was getting into this only because it was such a big famous problem, the controversy would continue for years to convince skeptics that more evidence was needed.

One criticism of the kt hypothesis was the lack of a crater of the correct type and size, Alvarez thought it should be 200 kilometers in diameter larger than the state of Connecticut, how can you ignore that they are looking for craters that were 65 million years old all over the Earth? Many of these things had been discovered. and it had been measured and found that two thirds of the planet is covered by water if the asteroid landed in the ocean crater it might never be found, even so, it would still be a trail of debris ejected from the crater, so the focus was on finding this. evidence that geologist Jean Smith discovered glass-like beads and Katie boundaries called spherules that formed when vaporized rock cooled and rained again.

Another key clue was rock that had been so impacted by the impact that it had crisscrossing bands of dislocated minerals. This was shocked quartz and we know that if you detonate a nuclear bomb, the damage caused to the surrounding rocks will produce shock quartz, so if you put two and two together we find shock quartz at the KT boundary and shock quartz and nuclear craters, You know that it is an explosion that deforms quartz crystals and quartz is only found on land, so there was the big clue: we have to look for a crater somewhere on earth.

The search for new clues took us here, to Texas, along the Brazos River, about 300 kilometers from the Gulf of Mexico. five million years ago this was the sea floor rather than grazing land in the early 1980s scientists noticed unusual sediment deposits along the river basin intrigued Alan Hildebrand then a graduate student in geology came to investigate along the banks of the river in its tributaries The examined exposures of the KT boundary are different from those seen elsewhere. I saw something on top of the Cretaceous mud and rock that once accumulated on the seafloor, so this is the typical newly founded mud in this area.

Exactly all we see is this chalky rain sludge. and there's seven million years of this mud here, so I mean we're talking boring, you know? Nothing was happening, but look, the seabed has eroded. At this point, an untrained eye could see this sediment and never look twice. in the protruding rocks, but hildebrand saw evidence of a catastrophic event, then something happened here, it eroded the seafloor and we started sayingthese very thick sediments and this first unit is really extraordinary because if you trace the route here you see here there is a rock in It is about 50 centimeters wide and you come here, this is another one, it was weak, so it is worn by the weather, but it is even bigger.

Here's another rock, but notice this rock is different from these ones, so you had this really regular layer of mud and then all of them. Suddenly this area is full of all this mix of rocks and from different places, it's not just the rock that was here at the bottom of the sea, maybe some of it was mined from deep water, maybe some of it was brought up from Chawla, everything. They got mixed up and dumped here, so what could have happened here that would explain something so dramatic? It had to be an enormously energetic wave in the ocean, a giant tsunami.

If an asteroid ten kilometers in diameter landed in the sea or on the edge of a continent, it would displace incredible amounts of rock and water, causing tsunamis more than 100 meters high. Giant waves would have crossed the sea with the speed of a jet, tearing up the seabed, moving tons of sediment while that debris settled in what is now the Brazos River Basin and would have been mixed with ejecta material falling from the sky. Well, now that we're here in Texas, does this make you think that you're a little bit closer to the crater in Texas and that you could be in Italy, for example, exactly because we can look at the impact products mixed in this konamide deposit, so let's we are warming up Hildebrand was on the trail of every new piece of evidence.

The next stop was Haiti, where he investigated a report of volcanic rocks, as he suspected they were actually ejecta filled with shock minerals and spherules. They also contained molten rocks called tektites. another telltale sign, more evidence that an impact had occurred somewhere around the Gulf of Mexico, but somewhere it wasn't precise enough. Ironically, a key clue discovered by another geologist had been long overlooked years before the combined field searched for oil in Mexico's Yucatan Peninsula. Nothing unusual was seen from the air and the field, but as instruments measured differences in gravitational fields and revealed the features of a giant buried crater, it was Hildebrand who ultimately followed Penfield's work.

Rock samples from the area Penfield identified showed all the signs of a high energy impact and were full of impacted quartz - so this evidence finally convinced everyone that there was indeed a large crater buried on the Akutan Peninsula after years. of speculation the crater had finally been found it was named Chicxulub crater in honor of a village built on its center The discovery of the Chicxulub crater was the definitive evidence of the asteroid impact and united all the clues that had been collected over the previous decade the crash woos to the tektites the rial sphere that had fallen to the earth, and the crater was the same, it was the KT limit and it was the size predicted by Louie Álvarez.

We now knew for sure what happened on that horrible day when the asteroid crater was finally found, but important questions still remained about which species were wiped out at the end of the Mesozoic, which ones survived, and why the search for those answers led to the Badlands. of the Dakotas and Montana in the Hell Creek Formation. Its eroded hills contain fossils of plants and animals that lived during the last million years of the Cretaceous and beyond, when paleontologists Kirk Johnson discovered this boundary KT with his telltale sphere Ewell found the dividing line between two very different worlds you are looking at a ball of glass that used to be the bedrock in Chicxulub Mexico Kirk how important it was to find the KT boundary here in North Dakota if you can put your finger on the battery like you can right here what that means you can ask a very simple question How life before impact is different from life after impact.

What I have to do is look for the fossils below, just compare them to the fossils above. and that's what we've done here for the last 30 years. This arid landscape was once a lush, humid forest. Crack open some rocks and you'll find leaves from plants and trees that flourished here more than 65 million years ago. You can even tell that the insects ate them, let's see that there are also two different types of insect damage on this leaf, instead of a feeding hole in the leaf and there is a margin that feeds on the, I would look closely at the soil and you can collect fossils of small animals that thrived in lakes, rivers and forests, so in my hand I have evidence of a turtle fish, a crocodile fish and a man, and then there were the dinosaurs, the challenge that connects their destiny with the KT limit, the clues from its fossilized remains, this is an ankle bone of a small carnivorous dinosaur and you find that these bones identify the animal and very soon you start putting together the list of dinosaurs that are present at any given level and the lower The younger you are and the closer to the limit you are, the more we address the question of how long the dinosaur survived, so right nearby we found this bone, which is a bone from a carnivorous dinosaur. much larger.

The same bone, but look at the difference in size, and here is exactly the same bone, so when you find bones of different species in the same layer, they live in the same place at the same time, the work requires a lot of time and patience, so It's basically how it is found. a dinosaur, you know, you're walking around looking at these bouncers and then you see a piece of bone, you can see it's very porous and since you know it had to travel by the force of gravity, you can see the trace of the bone, here's a bone . a bone follows the bone trail up and then here you have a really broken ductile dinosaur shinbone and then this is where it would articulate with the knee joint.

Scientists know that 22 types of dinosaurs lived in Hell Creek, including Triceratops Tyrannosaurus and this duckbill is about 9 meters or 30 feet long, the more complete the skeleton the easier it will be to reconstruct the past, but discoveries like these are extremely rare, you walk around you know, and the battle ends here and you will collect numerous pieces of asaurus dinosaur chunk that's what we call it and that's it, so you usually find piles of bones that are not articulated if they are not in the correct order, so having the vertebrae in the correct order like this is very, very rare and what makes this specimen even more important is its articulation and it is quite close to the KT limit.

Now I have found several specimens that are very close to the limit and really what that shows us is that even if dinosaurs are rare, if you look hard enough, we will find them when they lived on the planet. What we have not found yet is any dinosaur skeleton anywhere in the world above the KT boundary layer. Scientists now knew what lived here and its final fate a thousand kilometers from impact, death came quickly. If you turn on the oven, open the door and place your hand on the balloon. That's what the dinosaurs felt very early on and were probably roasted alive in about an hour.

For the more distant dinosaurs, death may have been delayed, but not for long, it soon vaporized. Ejection and smoke from the fires filled the air and a lot of sulfur may have also been released into the atmosphere because the impact site on the Yucatan Peninsula had a lot of sulfur and all that stuff was contaminated enough to erase the Sun without light, anything that depended on photosynthesis on land or in the sea was vulnerable as food chains collapsed, giant reptiles that were still alive died in the Mesozoic era, the era of dinosaurs ended and There were other radical changes in Kirk Johnson's lab in Denver, you can see what happened to the plants.

Life samples taken below the KT boundary show a high diversity of pollen grains remaining here in red, but above the boundary this former diversity disappears, reflecting the extinction of 60% of all plant species where any Once flowering plants prospered, ferns assumed the first transport, unlike the pollen fern. spores can germinate in an arid landscape devoid of living plants, we have a short period of time in which there are only ferns, that is the spike of the fern, but after that there are about a million years in which we have the low diversity disaster recovery flora and after that first million.

After years things start to get better again, we start to see animals returning to the landscape in this new post-impact world, the niche left by the dinosaurs was waiting to be filled and therefore the survivors of this on earth were creatures that lived in holes birds mice like creatures turtles frogs things that lived in swamps or rivers or near the seashore and compared to dinosaurs they had the advantage of size they were small small animals had a large population size small animals they had higher reproduction rates now it is not saying that the small animals did not suffer a mass death but a sufficient number survived and that is the key point in that million years of recovery the small ones inherited the earth it was the beginning of the era of the Mammals Eventually the largest mammals dominated the earth just as the dinosaurs had done before and among them were primitive primates whose evolution would lead in a very promising direction at least for humans, but the asteroid impact taught us about evolution that did not.

It is always about the survival of the fittest, sometimes it is about the survival of the luckiest and there is deep meaning to our species only after the extinction of the giant reptiles did mammals, including our primate ancestors, flourish, without the asteroid we would not exist