Published on February 25th, 2022 | by David Marshall
Episode 137: Tanis
The end-Cretaceous mass extinction was a cataclysmic asteroid impact that ushered in the end of the non-avian dinosaurs and forever changed the course of evolution on Earth. But what can we say about the timing of the event, other than it happened 66 million years ago?
Well, it turns out that Tanis, a relatively-recently discovered fossil site in North Dakota, is full of lines of evidence that are allowing earth scientists to piece together when the impact occurred.
In this episode, we’re joined by Melanie During, Uppsala University, who has been examining the details of the bones of fish to say more about the world either side of the event. This open-access study (from her master’s degree at VU Amsterdam) was recently published in Nature.
This video shows the record of impact spherules in the sediments at Tanis. As they hit the water and underlying sediments, they penetrated through, leaving a ‘funnel’ shape in their wake. Digging to the bottom of this, the spherule can be found.
Tanis is filled with numerous fossils of different organisms from different environments including fresh water, salt water and terrestrial (all three of which are shown in this video!). The sediments are soft enough that fossils can be dug out with a knife!
CT scan of a 3D paddlefish from Tanis with impact spherules stuck within the gills. Interestingly, none were in the digestive tract, so it can be determined that these fish were not living amongst the spherules for long. Googly eyes represent the front of the animal. Yellow circles represent the impact spherules.