We chat with Becca, one of our Museum educators, about the driving factors behind the disappearance of the dinosaurs during this Pulsar podcast brought to you by #MOSatHome. We ask questions submitted by listeners, so if you have a question you'd like us to ask an expert, send it to us at sciencequestions@mos.org.

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ERIC: After hundreds of millions of years, the time of the dinosaurs ended quickly and dramatically.

Today on Pulsar, we're asking one of our own educators, Becca, one of the most common questions we get at the Museum of Science. What happened to the dinosaurs?

I'm your host, Eric. Thanks to Facebook Boston for supporting this episode of Pulsar.

Becca, thanks for joining us, again, on the podcast.

BECCA: Thanks for having me, Eric.

ERIC: So I know the extinction of the dinosaurs is one of your favorite things to talk about. We have lots of great questions for you. But let's start with the reign of the dinosaurs.

Elias wants to know what the first dinosaur was and when it appeared.

BECCA: Yeah. You're absolutely right. I absolutely love talking about dinosaurs. But when it comes to the very beginning of the dinosaur reign, it is a little bit debated, mainly because scientists aren't entirely sure what the very first dinosaurs were.

In fact, there are quite a few that scientists think were very early on in the Triassic period, approximately 220, maybe 240 million years ago. But no one's totally sure.

One of the dinosaurs that people think might be the oldest one is Nyasasaurus parringtoni, which was approximately 245 to 240 million years ago. So that would be incredibly old. But some people don't necessarily think it was even a dinosaur. It might just be a very close reptile relative.

So if you take that into consideration, well, it might not be that one. It may be one a little bit closer to home, like Coelophysis, which was in North America from approximately 220 to 200 million years ago. A little bit more dinosaur-like based on scientists' different observations.

But again, it's one of those really heavily debated areas.

ERIC: So we don't know exactly when they first appeared. What about when they went extinct? Do we know that date with a little more certainty?

BECCA: We definitely do. We know that it was approximately sometime 65 to 66 million years ago. So that's a little bit more certain that it fell right within that 1-million-year range.

ERIC: OK. So the reason we're here. What happened to the dinosaurs? Why did they go extinct?

BECCA: Yes, that is the question. And it wasn't even the easiest thing to answer for a very long time. There were a lot of different theories. But the theory that is now most supported by evidence is that there was a giant impact - a meteor or asteroid.

Something from space hit the Earth just about 65 million years ago. And it caused a whole bunch of problems but, ultimately, led to the demise of about 75% of life on Earth.

ERIC: And we got a question from Amber about this object. How big was it? How huge does an impactor have to be to wipe out that much of the life on an entire planet?

BECCA: Yeah. This object was large. In fact, scientists estimate it was probably almost the size of Boston and was actually about six to nine miles wide. So that was a very, very large space rock that came. And it hit just off of the Yucatán Peninsula.

ERIC: Now, this was a cataclysmic event, but it was a really, really long time ago. What evidence led us to believe that an impact ended the time of the dinosaurs?

BECCA: Yeah. That's a really great point. We definitely have been able to see most of this 93-mile-long crater called the Chicxulub crater. But scientists, just last September in 2019, were able to drill into the Chicxulub crater and take out a 130-meter rock core sample

And they were able to determine, based on those rocks, what happened. The rocks provided evidence that there were tsunamis. There were wildfires. There was a lot of, even, melted rock in that area.

So that would have affected the dinosaurs in the local area, but they also gave us evidence that a lot more happened after the impact that caused most of that extinction.

ERIC: So locally, it was immediately devastating. What happened, on a longer time scale, to life around the globe, and how long did that take?

BECCA: Yeah. Excellent question. And certainly, many of the dinosaurs did go extinct on impact, especially if you were in the Yucatán Peninsula. That was an area that was very heavily hit.

But after that, what scientists noticed in this rock core sample is that minerals, like sulfur, salt, and gypsum, were all missing from the crater, which means that they went up into the atmosphere. They vaporized on impact. And they blocked out sunlight.

And that sunlight couldn't really get through to the plants. The plants couldn't really produce as much energy as they could before. Herbivores couldn't find as much food as they needed to survive.

And ultimately, the larger ones died off. Carnivores couldn't find as much to eat-- herbivores or other carnivores-- and ultimately, they were not able to survive.

And so, really, it was this extreme sort of rapid climate change from all of the debris in the atmosphere that caused most of that extinction. Now, anywhere from probably minutes to hundreds, thousands, tens of thousands of years after this impact is what this extinction probably was.

It wasn't necessarily about every single dinosaur went extinct on impact. But in fact, many of them, not being able to find enough food over thousands of years, ultimately died off.

ERIC: More gradual than we typically think of, but still really fast on a geologic scale. We did get a question from Logan, who wanted to know about other species that went extinct at this time. So can you talk about how other kinds of life on Earth managed during this period?

BECCA: Sure. So while we don't know exactly how many species of dinosaurs went extinct, we do know not all of them did and that some of them went to go on to become our modern-day birds.

But again, it wasn't just the dinosaurs. 75% of life on Earth included plants. It included other types of reptiles. It included mammals. And not all of the animals across all of these categories went extinct. But certainly, a majority of the life on this planet at that time didn't make it past this time period.

ERIC: So what was it about certain species of plants or animals that allowed them to survive this post-impact period? Was there a pattern of which ones disappeared and which ones didn't?

BECCA: There seems to be a little bit of one. And of course, it's different per different category of animals. But the more small the animal was, the better it tended to do because it could find more food.

So some of those smaller, more avian-like dinosaurs did pretty well, and they were able to find enough food and continue on and eventually evolve to modern-day birds.

But also, some of the smaller, more generalized mammals did really well. In fact, they no longer had giant dinosaurs trying to eat them, and they could find enough food. So they went on to thrive and fill all of the ecological niches that the dinosaurs once held and evolve into lots of different types of mammals.

ERIC: If some of the dinosaurs survived and evolved to become today's birds, what did they look like at the time of this extinction event? Did they already look a little bit like birds?

BECCA: We do think that some of them looked a little bit like birds. In fact, we think that birds, with their current feathers covering their body, came a little bit from the dinosaurs.

We think that dinosaurs, right before this extinction, had already developed some feathers.

In fact, you may have heard that people think the T-Rex had feathers on it. And certainly, quite a few other smaller raptors probably had feathers if not were completely covered in them.

So a lot of those characteristics on these smaller birds continued through the evolution of current, modern-day birds, including that look of this sort of smaller raptor covered in feathers.

ERIC: Now, avian dinosaurs and mammals have changed a whole lot since this time. Are there any animals that survived this extinction event that haven't changed in all that time?

BECCA: There definitely are. You may have heard that animals like crocodiles and alligators have basically been unchanged for this whole time, but also animals like sharks and other sort of animals that really haven't evolved because they haven't needed to.

They've been incredibly successful since, basically, the time of the dinosaurs for the past many, many millions of years, and they continue to thrive doing pretty much exactly the same thing.

ERIC: Now that we've heard all about this major change in the Earth's history, I want to ask you a question from John. He wanted to know, what would have happened if the dinosaurs hadn't gone extinct? If that impactor had missed the Earth, what would our planet be like today?

BECCA: This is one of my favorite questions because it's something I often wonder about myself. I love dinosaurs, but I also know that if the dinosaurs were still around today, life would be extremely different.

In fact, one of the things that I think about is that if dinosaurs hadn't gone extinct at this time period, the mammals probably wouldn't have had the same opportunity to kind of take over the world.

They would not be able to fill all of those ecological niches that those dinosaurs once filled. They would still probably be small, scrawny, and very generalized.

But instead, the mammals were able to evolve and diversify and, well, ultimately, millions of years later, become some humans. So perhaps we would not have been here if it weren't for this extinction event 65 million years ago.

ERIC: Well, thanks so much, Becca, for answering so many questions about the extinction of the dinosaurs.

BECCA: Thank you, Eric. That was fun.

ERIC: You can learn so much more about dinosaurs in the Blue Wing of the Museum of Science at our permanent exhibit, Dinosaurs-- Modeling the Mesozoic, featuring a full-scale Tyrannosaurus rex model and Cliff, one of the only near-complete Triceratops fossils on display anywhere in the world.

You can visit engage.mos.org to support the Museum of Science and MOS at Home.

Until next time, keep asking questions.

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