The Tanis Site: A High-Resolution Snapshot of the Asteroid Impact's Aftermath
The Tanis site in North Dakota is described as a rare, high-resolution record of the first minutes to hours after the Chicxulub asteroid impact 66 million years ago. Evidence includes fish with impact debris lodged in their gills, indicating they were alive during the fallout.
Key Details of the Event Deposit
A paper published in PNAS in 2019 describes an "Event Deposit" at Tanis, approximately 1.3 meters thick, capped by the iridium-rich clay layer that marks the Cretaceous-Paleogene (K-Pg) boundary. This deposit contains a dense mix of freshwater fish, burned wood, and marine ammonites, all laid down in a single, high-energy event.
- The surge was likely caused by seismic waves—estimated at magnitude 10-11—arriving within an hour of the impact, not by a tsunami, which would have taken several hours to reach the site.
- Spherules (glassy beads of melted rock) are found throughout the deposit, notably lodged in fish gills and sealed in amber.
- This suggests the fish inhaled the spherules while still alive and were buried shortly thereafter.
Evidence and Why the Gills Matter
The presence of spherules concentrated in the gill rakers of the fish provides a powerful temporal link. This indicates the fish were breathing during the fallout, fixing a precise moment in time—minutes to hours post-impact. This direct evidence makes Tanis a uniquely valuable site for understanding the immediate aftermath of the extinction event.
Controversy and Unpublished Claims
While the 2019 paper is peer-reviewed, several high-profile claims have been made outside of scientific literature, primarily in a 2022 BBC documentary. These include assertions of dinosaur remains at the site—such as a Thescelosaurus leg, a pterosaur embryo, and Triceratops skin.
- These claims lack detailed peer-reviewed publication and verification.
- The site’s rollout has been controversial, with a 2019 New Yorker article preceding the scientific paper, limited access due to its location on private land, and past scrutiny of lead researcher Robert DePalma’s work.
- Disputes over the season of the impact (a spring conclusion was reached by two groups) were complicated by allegations of data fabrication, which were not substantiated but led to findings of poor research practice.
Settled Facts
Despite the controversies, the core science remains robust:
- The Chicxulub impact 66 million years ago is well-established as the principal driver of the mass extinction at the end of the Cretaceous, supported by the buried crater, global iridium layer, and shocked minerals.
- Tanis, if the surge-deposit interpretation is correct, provides a rare, high-resolution record of the first hour post-impact at a single location.
- Open questions—including the full description of dinosaur material and independent verification—can be resolved through peer-reviewed publication and broader access to the site.