(ORDO NEWS) — The scientists’ conclusions are consistent with earlier studies based on plant fossils.
Dinosaurs were killed by a meteorite impact on Earth about 66 million years ago in what became known as the Cretaceous-Paleogene extinction event. Quite a lot is known about this event, but paleontology enthusiasts still manage to unearth new details of that catastrophe.
In a new study by geology bachelor and paleontologist Robert DePalma and his colleagues, scientists were able to find out what time of year a meteorite hit the Earth, and they managed to answer this question in an unexpected way – by studying the fossils of ancient fish.
The latest evidence comes from a site called Tanis, located in the Hell Creek Formation in North Dakota. Tanis is one of several geological sites in the world where scientists have observed the Cretaceous-Paleogene boundary in a sequence of deposits.
Remarkable fossils of dinosaurs, early mammals, fish, plants and more have been discovered at Tanis. Many of these fossils are exceptionally well preserved, and some show remnants of soft tissue such as skin as well as bones that can provide valuable scientific information.
The Tanis site was first discovered in 2008 and has been the focus of DePalma’s attention ever since. In a 2019 article, DePalma and his colleagues argued that Tanis captured the moment of the asteroid impact due to three factors.
First, the presence of dinosaur fossils found in the Cretaceous up to the Cretaceous–Paleogene boundary, and exactly at the boundary at the time of the impact. Secondly, the presence of a layer of tiny balls, consisting of molten rock, and then cooled in air or water.
The third evidence turned out to be seiches – standing waves that occur in closed or partially closed reservoirs. The Tanis site is far from land today, but at the end of the Cretaceous it was located on the coast of the western inland seaway that divided North America at the time, with sea levels about 200 meters higher than today. The place was estuarine, which means that fresh and salt water mixed here.
The seiches were caused by a distant impact in Mexico that generated seismic waves that shook the Earth and caused water to flow in and out of river channels at high speed. According to scientists, these processes began here about an hour after the collision.
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