Why the Dinosaurs’ Extinction is an Ongoing Puzzle | Nat Geo Explores

[Music] This happened about 66 million years ago. The impact was as powerful as 10 billion atomic bombs. From the catastrophic global effects on the environment were even deadlier. Seventy-five percent of life on Earth went extinct, including a dominant group of animals that has come to mesmerize our attention. The diversity that we see in dinosaurs is really a reflection of how successful they were. Meet Nat Geo Explorer Diego Pol, one of the paleontologists who discovered the largest dinosaur ever.

Dinosaurs were predominant in our world for over 140 million years. Humans have been on this planet for two hundred thousand years, and there are not many cases in the history of our planet where one group is so predominant and so successful for such a long time. Humans and dinosaurs didn't overlap—not even close. And as we've seen in Hollywood, we can be thankful for that. But dinosaur fossils left humans wondering: where did they go? Dinosaur extinction has been a fascinating topic for a long, long time. We see their presence up to 66 million years ago, and then after that, there's nothing—they're gone.

Throughout the 20th century, there were a lot of arguments and theories that varied dramatically, from the somewhat plausible to the downright bizarre. Some pointed to out-of-control hormones or cataracts. Others blamed a world taken over by hungry caterpillars. The answers eluded experts until Natal 18 when two scientists working here discovered a clue. The link to it being an asteroid impact started almost by accident. Walter Alvarez and his father, Louis Alvarez, were actually very interested in a place called Rubio, Italy. There were limestone deposits that were from after the Cretaceous, what we call the Paleogene, and that the extinction event was right at that boundary.

Instead of finding anything sort of background normal, they actually found a spike in something called iridium. Iridium is a surprise because we have very little iridium present on the surface of the Earth versus what the asteroids are made of. Walter and Louis Alvarez co-authored a groundbreaking paper hypothesizing that an asteroid was responsible for the mass extinction. But that in itself raised another question: where's the crater? Scientists dug further into the layer of iridium for answers.

The real key clue was that while it's only a centimeter-thick layer in most of the world, as you approach the Gulf of Mexico, that layer becomes much, much thicker. They started seeing layers that are a meter thick or even hundreds of meters in places as you get closer and closer to the place where the impact happened. By the early 90s, the science was becoming more convincing. More than three thousand feet below the surface of the Yucatan Peninsula laid a saucer-shaped structure, different from volcanic terrain. This was the Chicxulub crater.

So to answer the fundamental questions about how this particular impact caused a mass extinction event, we needed to drill into it. Where it actually hit was limestone, so calcium carbonate, which makes a lot of CO2 when you vaporize it. But even more importantly, perhaps, were evaporites. These are rocks that are high in sulfur, and so when those get vaporized, they actually put native sulfur into the atmosphere, which when combined with water becomes sulfate aerosols—a pollutant that actually succeeds in cooling the planet off.

If it had happened a little bit earlier or a little bit later in terms of the rotation of the Earth, it could have easily hit the Atlantic Ocean or the Pacific Ocean and entirely missed this shelf environment with all these sediments beneath it. If it had done that, most of the material that would have been ejected would be the vaporized asteroid and just water where it hit. With the energy it hit, it seemed to have had the right recipe to create a global catastrophe. Dinosaurs were likely living in a vulnerable time leading up to the asteroid.

But perhaps more surprising is the realization that not all dinosaurs went extinct. Most people think that dinosaurs are extinct, but this is completely false because, you know, if you look out your window, you're gonna see a living dinosaur. [Applause]

As a vertebrate paleontologist, my specialty is understanding how birds evolved from dinosaurs and then also how the earliest birds evolved into what we would consider a bird today. You have this huge diversity of Dinosauria, and then you have one group that's called a theropod. Everybody knows theropods; it includes famous members like Velociraptor or T. rex. But one group of theropods eventually gave way to birds. This resilient group of theropods is represented today by over 10,000 living species of birds. Modern birds are the most diverse clade of vertebrates living on land on the planet today.

So, people are always saying that this is the age of the mammals. I always like to joke and be like, "It's still the age of the dinosaurs." While the dinosaur extinction mystery has come a long way since the early theories, discoveries today are still necessary pieces of the bigger picture. You have to like puzzles and discovery; it's certainly important, but it will not answer all your questions. It will be a big and important piece of your puzzle. Mass extinction events are incredibly powerful tools for us to understand the way life and ecosystems operate.

So, the Chicxulub event is the most recent of these mass extinction events on Earth. Science is never done, right? We just find more questions that need answering. You. [Music] [Music]