Although we tend to think about the Iridium layer as a marker of the moment of impact, it is really a little late. The layer is formed by small dust particles that crash into the atmosphere at the impact, and they remain long enough to spread evenly around the world. By the time they were established, many of the worst effects of the impact – the tsunami and the earthquakes – had come and gone, and the global fires were in full swing.
If the iridescent layer is a bit late to fully understand Chicxulub's influence, the sites are too early, consisting of rocks that have already been put in place before Chicxulub.
The Tannis deposit consists of about a meter of material that appears to have been deposited during two floods, with larger heavier particles in the lower layers and finer, lighter materials above them. The bodies of the animals and the trees, along with the streams of the stream, are also in line with a flood, equated with the prevailing current. There was only one odd thing about it: the lower layer seemed to have been deposited, as the water rushed into the ocean .
According to the hill where the deposit is left, the flood is estimated to be at least 10 meters deep.
t were deposited after the action of Chicxulub, but before the iridium layer was postponed. There are small fragments of material scattered all over the deposit that are typical of debris: shocked minerals and spheres of materials that shape the glass as it quickly cools in the atmosphere. Chemical analysis indicates that they are indistinguishable from similar materials found elsewhere that originate from Chicxulub. Argon of the material produces a date (65.76 million years), which coincides with that of the impact
The next key question is how this material has reached the Tanis deposit. If the flood has destroyed a deposit from the Chixoulub era elsewhere, you could see a similar material. But the researchers make a convincing case that this has not happened here. Part of Chicxulub's material is embedded in amber, which implies that it has hit the wooden juice that is flooded by the flood. Another material was found in the gills of the fish that died in the place. And many of the particles were found at the bottom of a few ruins in the sediment, with patterns that "suggest that the downward sphere fell at the ultimate velocity of an open, soft surface between the two main impulses."
Time is all this
this places limits on the time when the flood occurs. It had to happen quickly enough that the iridium layer was not yet glued. It was supposed to happen before the heavier material – the shocked minerals and glasses – had fallen from the sky. This creates a possible window between 15 minutes and two hours after impact.
This time period excludes the possibility of a flood caused by a tsunami, as it would take 18 hours to reach North Dakota by the impact in Yucatan. (It is also unclear whether a tsunami can find an adjacent waterway through the Western Inner Maritime Way.) Instead, the authors suggest that the flood is the result of a seismic phenomenon called seismus in which a resonance of seismic waves causes the emergence of waves in a limited water body. They point to the example of the Tohoku earthquake in Japan in 2011 that caused the 1.5-meter wave in the Norwegian fiords
This earthquake has a magnitude of 9.2; It is estimated that Chicxulub has caused seismic disturbances that may have reached 11.5. The waves would begin to reach North Dakota six minutes after the impact, the last passing about 15 minutes after the blow. So the time is right for this theory to work. However, the researchers acknowledge that they can not exclude floods caused by extreme winds driven by sudden temperature spikes or a seismic event causing landslides that have pushed the floods into the interior.
One of the Big Questions about the Chicxulub event is its role in mass extinction. Did the dinosaurs have climbed to the brink of extinction, thrown out of them by the huge eruptions of Dean's traps? Or is life flourishing until the moment of impact? The site Tanis will not answer these questions, at least not immediately. The paper itself does not mention bones of dinosaurs. Instead, most of the described species are either plants or aquatic organisms
On the freshwater fish side, fish include saliva and sturgeon. The species of the two groups have survived to this day. Sea species include many ammonites, an animal in shell that resembles Nautilus and is almost universally distributed in marine fires before the impact. The Ammonite, however, ended with mass extinction.
But the biological material is given in a few scant paragraphs in a very important book. It is likely to be described separately in a number of articles, so we are likely to be able to say more about ecology before extinction when these details are revealed. But the true value of Tanis may be how much he can tell us how to find similar sites elsewhere.
Researchers who discovered Tanis, however, are already faced with some disputes about how they have distributed the details. Robert Depalma, the student who made the discovery, shared his details with a journalist from 2013; only recently presented some of the results of a scientific meeting. Researchers, PNAS and one publisher, then work together to publish an article in an article in The New Yorker . For several days last week the paper itself was only available to journalists who registered for emails from PNAS ; scientists and the rest of the press were left to make a copy.
A picture given to the press by Depalma also shows tritratopes swept up in flood waters, something the paper does not provide evidence of.
Nothing of this takes away the excitement of the discovery or the prospect that further work will confirm that this locality is made within hours of Chixoulub, but this affirmation will require the larger scientific community to gain greater access to the material
PNAS 2019. DOI: 10.1073 / pnas.1817407116 (For DOIs)