Scientists now widely believe that most dinosaurs became extinct about 66 million years ago as a result of a powerful asteroid impact that struck the territory of the current Yucatan Peninsula in Mexico.
This impact changed the history of life on Earth and paved the way for the emergence of mammals and, ultimately, humans.
Now an international team of researchers has said it has found fossilized remains of fish and a dinosaur in North Dakota at a site they called “Tanis.” They believe the creatures died on the day of the asteroid’s impact.
This story is told in a new documentary called “Dinosaur Apocalypse” coming out on WTTW.
Robert DePalma, who heads the excavation of the Tanis site, spoke with WTTW News. DePalma is an adjunct professor in the Department of Geological Sciences at the Atlantic University of Florida and a graduate student at the University of Manchester, England.
Tell me about the Tanis site in North Dakota, I understand you have been studying the site since 2012. What drew you to this site?
Robert DePalma: It all started with a team of commercial collectors who have worked there for many years. They extracted and sold fossils from Hell Creek. They came up to me and said, look, we have this amazing site that has a lot of fish. This is really very unusual because no fish is really known from Hell Creek. Until now, maybe three were known. They are not so common. When we looked further, it was very, very easy to notice that the sediments there indicated that the deposition scenario was very turbulent and turbulent and involved a large splash of water. And this surge came inland. All the rivers then flowed east into the giant sea route that divided the United States into two parts. And the surge that caused this field, went in the opposite direction – went inland.
Then we noticed there the sea fossils we were expecting from the sea route. So this confirms that we have a surge. Then we start to see all these pieces of ejection, these glass spheres that came out of the sky that were exploded from the crater. And the area is closed by a layer rich in iridium (from an asteroid impact), and this layer, and emissions, and everything else dates back to the time of the impact of Chixulub and geochemically corresponds to the fingerprints of the impact. So, basically, we have a site that is fixed in time, the first moments after hitting one of the most significant impacts in Earth’s history, one that led to the end of the Cretaceous.
As you know, there are skeptics about your claims who say you need to do more research before they are ready to accept your interpretation of what the Tanis website presents. What do you answer to these skeptics?
DePalma: You will never make everyone agree on everything … but my team includes some of the leading minds in the field – Walter Alvarez (who, along with his father, Nobel laureate physicist Luis Alvarez, theorized that an asteroid strike killed most dinosaurs) – You would not even know about this blow, if not for Walter Alvarez. We have assembled a dream team of truly specialized senior researchers to explore this. We have at least three different teams going to join us this summer. It’s a wonderful collaboration of minds and talent, and that’s what leads us to the conclusions we’ve come to now.
What is the Tanis site now and what was it like 66 million years ago before the asteroid hit, which is believed to have destroyed most dinosaurs?
DePalma: At this very point it would probably be very damp with a little snow, so I’m not digging right now. But on any ordinary day of excavations you will see typical barren Hell Creek areas. You will see rocky rocky outcrops, you will see meadow grass. You can see the occasional rattlesnake. Now this is in stark contrast to what was then. I now live in South Florida and it is very close to the type of climate you saw at the end of the Cretaceous. In fact it’s a little colder now because there weren’t ice caps on the poles then because it was so warm. And then it would be a paradise from tropical to subtropical. One of the conclusions from the research we are conducting there is that we see signs of an absolutely bright life at the time. He was not in decline, dinosaurs and all other terrestrial animals and plants, everything was then bustling. And for all intents and purposes, it would be a prehistoric paradise before the impact.
You and your team have made some unusual discoveries, including the exquisitely preserved leg of a dinosaur that you believed died on the day of the asteroid’s impact. What is the evidence for that? How can you so accurately tie your findings to the day of the strike?
DePalma: This is a great question. As scientists, we never jump to conclusions. This is not what you do in science. In this way, you allow clues and data to speak for themselves and they will tell you a story. And in terms of the site itself, the actual site is mostly limited to the moments after the hit in various ways. The surge of precipitation is full of discarded balls (small glass droplets) that were mostly deposited when released from the air after impact. They only appear, maybe an hour, maybe two hours maximum, after hitting an asteroid. Walter Alvarez did the calculations himself.
You then add to this that the site itself is covered with an intact layer of this very, very fragile, fine-grained border clay KT, enriched with iridium and shock quartz and all that. Thus, the site itself is blocked in time, and this is the maximum of the first hours after the hit. As for animals and plants, it can be determined that most of them became direct victims of the surge. They were alive by the time they were buried. As for fish, most of these fish have discarded balls pressed into their gills. These things were enough for oxygen-saturated water in this muddy water splash. And these balls came out of the sky, and the fish sucked these things into their gills.
You have been studying the site for ten years. When did you first realize that something really special could be in your hands?
DePalma: It was a kind of step-by-step process. At first we thought we were the happiest people on earth because we had a plot full of fish when there were only a few fish in the Hell Creek Formation. So we thought, dude, that this is an incredible opportunity to study the early evolution of the otter and sturgeon and these Cretaceous fish, of which very little is known. And we were about it.
And then when we found out it was a burst event that occurred at the time of the asteroid’s impact. This changed the game because this realization happened in about the first year of working on the site. We found the wreckage in the first year, but then we had to bring them back and analyze because obviously you don’t want to jump to conclusions. After analyzing this debris, we could say that the date corresponded to the KT limit, when there was a sudden mass extinction of about three-quarters of plant and animal species on Earth about 66 million years ago. The geochemical signature corresponded to the impact, all pollen signatures on the site corresponded to the late Cretaceous. When all these pieces came together, we were absolutely thrilled and we realized that every step forward we make in this deposit is a historic step and we can potentially find something stunning.
Note: This story will be complemented by a video.