Science Friday
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In a conversation from 2022, Dr. Riley Black discusses what happened after a massive asteroid hit Earth.
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What would it have been like to witness the last moments of the dinosaurs just after the asteroid struck the Earth?
It raises the air temperature all around the planet to about 500 degrees Fahrenheit. So if you ever broiled a chicken, that's about what you broil a chicken at. And T-Rex was more or less a broiled chicken within about 24 hours of this impact.
It's Tuesday, December 3, and you're listening to Science Friday.
I'm Sci-Fry producer Dee Peterschmidt. We're returning with more of our listeners' favorite segments for our 33rd anniversary. And today, we're going back in time, first to 2022, when this interview originally aired, and then way back to explore what happened on Earth after that massive asteroid wiped out the dinosaurs. Ira Flatow talked to an author of a book that traced what happened from the immediate aftermath to thousands of years later.
Joining me is Riley Black, author of The Last Days of the Dinosaur, based in Salt Lake City, Utah. Welcome back to the show.
Thank you so much for having me back on.
You're quite welcome. You know, I know you have written several books, many about dinosaurs. Why did you want to focus on the last days of the dinosaur in this book?
Yeah, I realized that I hadn't really done justice to the story, to borrow that Seinfeld line, I kind of yada yada this extinction, right? Because a big rock strikes the planet, we assume that it's, you know, going to cause a mass extinction somehow. But there have been other impacts at other times I had nothing to do with any major extinction event. So this seemed different. And I realized I didn't know as much about it as I probably should. And the more that I started to research on this, and I mean, paleontology might beat, I write stories about some of these new discoveries, I realized that I had the story kind of not entirely wrong, but I didn't understand how much we had learned about it.
Yeah. Well, let's begin where you just left off there. You say in your book that there have been other impacts of similar or greater scale that did not trigger biological disasters. So what was it about this impact that did?
Yeah, that's the really strange thing, because it's not as if this asteroid or whatever this body of rock was, we're pretty sure it was some kind of asteroid, a carbonaceous chondrite, I think is the best working hypothesis right now. It wasn't just hanging out, you know, near Earth and decided to stop in. It had been traveling towards our planet for a very, very long time. And this was kind of like a galactic skill shot, in a sense, like, you know, it could have just as easily missed or come closer, hit somewhere else on the planet. But the fact that it hit at an incredible amount of speed was so very big. And it hit all this limestone. So basically, these ancient fossil deposits, the ancient remnants of reefs that had existed millions of years before the impact itself, that contained all these chemical compounds that contributed to the impact winter. So
when you put all these things together, the size and the speed, the angle at which it hit, the sheer force of it. All these things came together and basically the worst case scenario that nothing quite like this has ever happened before in Earth's history and certainly not at such sort of a vulnerable moment for for life on Earth. And all these things came together, not just in the first 24 hours, we had this incredible heat pulse and all this debris, but in the years following. So it really was every single way that this could have gone wrong for life on Earth. Just about that's how this played out. It's really spectacular how quick and violent this was.
Yeah. So it was the perfect asteroid storm, you're saying is what it is.
Oh, absolutely.
Yeah. Let's talk about the sequence of events. And that's what you do in the book. You go through the first days, months, years, eons, thousands, million years. Let's look at the timeline on this. You write that this calamity was as immediate and horrific as a bullet wound. Explain that.
Yeah. So when we think about this mass extinction, or at least a lot of the visuals that I get or got growing up about this mass extinction, you'd see these emaciated dinosaurs wandering through this like nuclear winter kind of scenario that they made it through the first day, but it was really the debris clouds and the cessation of photosynthesis and all these big environmental changes. But we now know that they probably didn't even make it that far, that basically all our favorite nonavian dinosaurs, T. rex and triceratops and montasaurus and all those were probably gone within about the first 24 hours. Because what happened in the minutes to hours following this impact, you had all this pulverized rock, so millions of cubic miles of rock that's been thrown up into the atmosphere
that start to spread, basically this start to spread all over the planet. And as they're coming down, each one, each little piece is creating a significant amount of friction by itself. Any one of those isn't very much, but you do enough of that. It's just so much debris and so much basically damage created by this impact that all that friction creates an infrared pulse. It raises the air temperature all around the planet to about 500 degrees Fahrenheit. So if you ever broiled a chicken, that's about what you broil a chicken at. And T. rex was more or less a broiled chicken within about 24. Four hours of this impact that if you couldn't get underground, if you couldn't get underwater in somewhere, had some other way to block yourself from this pulse.
Wow.
You're basically out in the open. It was so hot that some forests were spontaneously catching fire based upon some of these models that geologists and paleontologists put together. So it really was incredibly extreme.
And then we had a cold period.
That's right. About three years of impact winter. So you had this terrible heat pulse that did most of the major initial damage. But in the years that followed, you not only had the soot from forest fires all over the planet, you not only had all the dust and debris thrown up by the impact itself, but all these sulfur based compounds that we know from observations during our own history are really good at reflecting back sunlight. So it's estimated that the sunlight reaching the earth was reduced by at least about 20%. And that was enough to curtail, if not stop photosynthesis over much of the planet. And if you take out plants, that's the basis of our ecosystem, it's the basis of our oceans, it's the basis of how we get our oxygen. It's something over those three years that not only temperatures dropped,
but ecosystems almost entirely collapsed and those survivors during those three years had to get by on scraps.
There was one factor that made this extinction not as bad as it could be, you write, and that's a very unlikely source. And I'm talking about volcanoes. Can you explain this?
Yeah. So in the past, we've had at least five mass extinctions so far. We may be entering a six, but most of those five or at least a significant number of them prior to this asteroid impact at the Cretaceous were caused by volcanic activity. And in particular, prior to the asteroid impact and after the asteroid impact 66 million years ago, had incredible outpourings in what's called the Deccan Traps in what's now India, just, you know, thousands of miles just covered by molten rock and all the greenhouse gases that are being spewed into the atmosphere as part of it. And those greenhouse gases, in fact, counteracted some of the effects of impact winter. This is not what we think of when we think of volcanic eruptions like this. We often think
about about them in terms of causing extinctions, but In this case, it kept the impact winter from being as bad as it otherwise could have been at raised temperatures, just enough to allow some forms of life to be able to survive. And otherwise, it would have gone extinct in the chill of that impact winter. So even though those volcanic eruptions were previously considered to be a contender for this extinction, it turns out that they kind of mitigated the effects of the asteroid impact and kind of came to the rescue for at least some forms of life.
Yeah, that is really something new that we haven't heard before because we've heard of research that says that dinosaurs were already weakened by natural forces and possibly volcanoes. They were on their way out and the asteroid just provided that final push. But are you saying that's not true?
That's right. It's it seems to be the opposite case, that volcanic eruptions actually assisted some of these surviving animals. Most of the non-eating dinosaurs, if not all of them, are already gone by the time, you know, this counteracting force would have come into play. But that's the other part of this is that so much of what we understand about this extinction comes from Western North America, comes from the Hell Creek Formation, the overlying rock layers in Montana and the Dakotas. There's so much that we don't know. So the decline that paleontologists previously thought they saw is because there are fewer rocks from the relevant time period. So just as an absolute level, we have less dinosaur diversity because there aren't as many rocks from the very end of the Cretaceous that actually preserved them as compared to 10 million years before.
So we're really learning in a sense, how much we didn't previously know about this mass extinction and how it played out.
And how long did it take for plant life to come back?
Yep, there's a seed bank or there was a seed bank in the soil. So a lot of plants, you know, they spread their seeds, they spread nuts, they spread their fruits as far as they possibly can. And some of those already existed in the soil and would have been shielded by some of the heat effects. It really only takes about a couple of inches of soil to really shield what's in the soil from the effects of things like forest fires. We know from modern day forest fires, they get about as hot as that infrared pulse that it doesn't take all that much. So that seed layer was there, it actually allows beaked birds to survive. That's why we have dinosaurs around us now is because beaked birds were able to subsist on the seeds and nuts that still existed.
But it took at least about 100,000 years before you started to see vegetation make a real recovery. You have what's called a fern spike, where we see fossil ferns and their spores everywhere in the fossil record around this time. And that's because ferns are what we call disaster taxa. They're really good at coming into spaces that have been disturbed, that have been disrupted. And they're kind of the first initial signs that life is beginning to recover. And then about a million years after impact, that's when you start to have these thick, dense forests starting to grow up, that you have the rise of flowering plants and angiosperms rather than conifers. So it took about a million years before anything recognizable as a forest started to reestablish itself.
After the break, how birds and other animal and plant life reestablished itself post-asteroid impact.
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And one of the interesting topics you talk about in the book is the evolution of the bird life following the impact. In fact, I found it fascinating to learn that it was the evolution of a beak and not the teeth of the dinosaur birds.
That's right.
That allowed these birds to survive. What's there about a beak that nature likes?
Yeah, we've had beaks evolve multiple times, you know, over and over again. In the case of dinosaurs, why beaked birds were able to survive. If you think about what birds and bird-like dinosaurs were doing prior to the impact, you had basically things like velociraptor covered in feathers, you know, very sharp teeth. We had toothed birds that were able to eat insects and lizards and things like that. And then you had beaked birds that primarily ate seeds, nuts, plant material. They were already adapted to this kind of diet. They probably already had things like a gizzard or ways to grind up that plant food. So they're, in a sense, were pre-adapted to life after impact. Whereas all those carnivorous species, there's nothing for them to eat because there are
no more plants, therefore no more insects, there are very few small little critters for them to eat. So basically, if you were a carnivore, trying to survive through this impact winter is much, much more difficult. Whereas beaked birds, they were already adapted to eating things that had survived. And that's why they're able to hang on.
Interesting. So what else was different about plant and animal life post impact?
You see forests grow a lot denser. If you think about forests and habitats in the age of the dinosaurs, basically in those, that end Cretaceous heyday, it would have looked somewhat similar to areas in like Eastern Africa today. So more conifers than flowering plants, there's certainly no grasses, but that kind of open habitat and open woodland, because many dinosaurs were big. Where they walked, where they pushed over trees, where they fed, this all influenced the ecosystem and shaped it around them. So you're going to have dinosaur sized holes, basically through any ecology that you're looking at. But once they were gone, once you don't have things like triceratops mowing down vegetation or pushing over trees anymore, forests could grow a lot denser, they could grow a lot
closer together and they could grow tall. And that provided a multi-tiered ecosystem for their survivors, whether you were a bird or a mammal or an insect, life could be different at the canopy than on the trunk of the tree, than at the surface of the soil or down below that soil. So you had all these different new opportunities for evolution and pioneering new niches open up.
Right. This is Science Friday from WNYC Studios, talking to Riley Black, author of The Last Days of the Dinosaurs. Really interesting. As I said in the, in the opening, I read a portion of your book where you said, "We," meaning humans, "we wouldn't exist without the obliterating smack of cosmic rock." Why is that?
There's no reason to think that the age of dinosaurs sort of stopped without this. I mean, in a sense, we still are because we're still here. But the kind of dinosaurs that we think about and see in the movies all the time, they would still be here. If you think about 66 million years, there's a very long time. But if you were to start from the day before impact, so you know, T. rex and triceratops are still doing fine, project that backwards 66 million years further into the Cretaceous. Dinosaurs are still around, they're doing fine. Like basically, there are more time, there's more time between stegosaurus and T. rex than there's been since T. rex went extinct. So dinosaurs were the dominant vertebrates on land. They're the most prominent vertebrates on land for so very long. And they'd survived so many different changes between the continents
moving around, volcanic eruptions, climate changes, sea level changes. They would have made it through. It took something really unexpected and unprecedented to really change up life and what it was. And our ancestors could have very well gone extinct in this very same extinction. It's one of the things that blows my mind, honestly, is that there were primates around during the last day of the Cretaceous. This little animal called Purgatorius is the earliest known primate. And it was able to survive where the big and terrible dinosaurs weren't. So it's not just that we evolved as a result of this extinction, but our ancestors, our primate ancestors, actually eat right through it.
That is cool. Are there other things we can see now that are direct remains of this extinction?
You can look almost anywhere, basically, whether it's seeing all the flowering plants and their pollinators. That's something that those interactions and those kinds of plants were around before impact, but they're much more prominent now. Or things like beans. Yeah, you, I loved a good taco. I like to put refried beans on it sometimes. Beans only came about because legumes evolved about a million years after impact, that plant life got this re-inferiorated kind of evolutionary pulse after the impact. And basically, plants like legumes that are rich in protein are part of that as well. So whether it's just our own existence, or what we eat, or the sort of vegetation we see around us, there are so many little hallmarks that we can draw back to this massive extinction.
Who knew how important beans were? As, as you say, Riley, you've written a lot about dinosaurs and written many books. What surprised you the most about writing this book and your research?
I felt like so much of it was a surprise because I had so many assumptions going into it. I think what really struck me was How the way the world recovered after impact, how relatively quick that was. I mean, a million years is a long time, but to think that prior to the mass extinction, the largest mammals that we know about were about the size of a house cat. And then a million years later, the largest mammals that we know about were about the size of a German shepherd, and that's quite a bit bigger. And we're starting to understand so much of how and why they evolved and the pattern of their evolution. There's a paper that just came out. I wish I could have included it in the book, but it's still fascinating to me about how mammals were getting big so quickly that their brains pretty much remained at the same size as they had been post-impact.
So that you have much bigger bodied mammals, but their brains are about the same size. And it wasn't until about another 10 million years or so after that, after impact, that you start to see a lot more sort of changes to the prefrontal cortex and changes in behaviors and interactions and things like that. So that life really raced to fill in the voids that were left by this mass extinction in such a way that it was a really formative and interesting time for evolution in general. Like, it wasn't a sense of progress or mammals picking up the torch where dinosaurs had left it. But there was something entirely new happening. And seeing and understanding some of these interactions that we never got to view before. So much of this research has come out in the past five or 10 years.
You know, even the last year, we've made a lot of new discoveries. So this is rapidly changing and giving us this view, this timeline that we never really had before.
That conversation with Riley Black, recorded in 2022. You folks chose it as one of your favorite segments from our 33 years. And if you didn't hear your pick today, don't worry. We've got a few more favorites to pull out of our archives during the December holidays.
And that's all the time we have for today. Lots of folks helped make the show possible, including Annie Nero.
Jason Rosenberg. Rasha Ureidi. Shishana Buckstun.
Speaking of going back in time, tomorrow we'll be revisiting when the band They Might Be Giants visited Ira in the studio to play and talk about songs from their album Here Comes Science. I'm Sci-Fry producer Dee Peterschmidt. Thanks for listening.
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