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Scientists find fossilized fish possibly blasted by debris from asteroids that ended the dinosaur age



Plaster cast of a Tanis deposit fossil showing a freshwater fish (dark brown) next to a marine ammonite (shining above left).
Photo: DePalma et al. (PNAS 2019)

At one of the most important earth cemeteries in North Dakota, paleontologists discovered the fossilized remnants of fish that seemed to have been killed by the effects of the asteroid that ended the Cretaceous.

We know that 66 million years ago, a large asteroid hit Earth, and at the same time dinosaurs died out. We're not entirely sure if the asteroid alone was responsible for the mass extinction, but you might ask, "Should not we see remnants of animals killed by the effects of the asteroid?" Well, we have found some now.

This is the last day of the Cretaceous, "said David Burnham, a professor in the Department of Geology at the University of Kansas and one of the authors of the study, told Gizmodo.

When a huge meteorite beats, expect chaotic effects, such as rocks altered by the high pressures and temperatures of the impact, huge earthquakes and tsunamis. However, the Earth's rocks do not directly preserve individual days of the multi-billion-year history of the planet. You have to get creative when it comes to separating the geological data. For example, 66 million-year-old rock strata around the world appear to contain excess iridium, believed to have been deposited by the Chicxulub impactor, located near the present-day Yucatan Peninsula in Mexico. Then there are tektites, small, glassy spheres of compressed and heated rock. Theoretically, there should also be fossil evidence that animals were killed by the effects of the asteroid.

The Tanis Formation
Screenshot: DePalma et al. (PNAS)

This is what makes the new research led by Robert DePalma at the University of Kansas, so exciting – the description of a pair of sedimentary eaters at the Tanis site of the The Hell Creek Formation in southwestern North Dakota. Both layers contain an excess of iridium, but only the bottom layer contains pieces of glass that appear to have been deposited by a land moving force. They think that they observe two events: the upper layer is the dust settling after the impact. The lower one is a large sediment deposit from the hours after the impact.

But if you can not convince the rocks alone, maybe the fossils in the event deposit will do this. During the Cretaceous, a large stretch of ocean traveled through the interior of the United States and ended near the Tanis region. However, the rocks of Tanis preserve a mix of both freshwater fish such as paddlefish and sturgeon, as well as molluscs called ammonites. This indicates that the sea had mixed with freshwater rivers at that time. And there were more glass balls in the gills of the petrified paddle fish. It seemed as if a wave containing shocked glass from the impact of over 3,000 miles hit the area, and the fish had inhaled some of them in their dying breath.

X-ray showing gill beads embedded in a paddling fish.
Image: DePalma et al. (PNAS)

Other researchers were impressed by the work. "When I first read it, I kept saying 'wow, wow, wow,' said H. Jay Melosh, a distinguished professor of Earth, Atmospheric, and Planetary Sciences at Purdue University, to Gizmodo," I think that This is a snapshot of the time the deaths occurred right after the impact. "

The researchers point out that there are other scenarios that may have led the glass particles to Tanis There may have been meteorological events such as storm winds or landslides, the authors write in the PNAS paper.

But the observations have far-reaching implications, and the authors write:

"Observations at Tanis expand our understanding of the harmful effects of Chicxulub and its far-reaching sphere of influence.The most probable connection between the d Shock-induced seismic shaking and the rise of land-based floods at Tanis reveal an important additional mechanism by which Chicxulub's impact could have caused catastrophic conditions in the western interior and possibly worldwide, far from the point of impact.

It's amazing to imagine how life on Earth has changed abruptly in the hours and days after the Chicxulub asteroid. And it is also amazing that we have been able to find direct evidence from that time in the remnants of the creatures that have experienced it.


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