Chicxulub impact occurred during northern spring or summer: study

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About 66 million years ago, a 10 km-wide asteroid crashed into Earth near the site of the small town of Chicxulub in present-day Mexico. The impact released an incredible amount of climate-modifying gases into the atmosphere, triggering a chain of events that led to the extinction of non-avian dinosaurs and 75% of life on the planet. According to a histological and histo-isotopic analysis of a unique assemblage of fossil fish from North Dakota, USA, triggered by an impact, the impact of Chicxulub occurred during the boreal spring / summer, shortly after the spawning season for fish and most inland species.

The Chicxulub impact 66 million years ago generated a tsunami-like wave in an inland sea that killed and buried fish, mammals, insects and a Triceratops, the first victims of a cataclysm that led to Earth’s last mass extinction. Image credit: Robert DePalma.

“The time of year plays an important role in many biological functions such as reproduction, feeding strategies, host-parasite interactions, seasonal dormancy and breeding patterns,” said Dr Robert DePalma, researcher at the Charles E. Schmidt College of Science in Florida. Atlantic University and the University of Manchester.

“Therefore, it is not surprising that the time of year for a global danger can play a significant role in the severity of its impact on life.”

“The seasonal timing of Chicxulub’s impact has therefore been a critical issue for the history of the Late Cretaceous extinction. So far, the answer to this question has remained unclear.

Dr DePalma and his colleagues examined the locality of Tanis in southwestern North Dakota to understand the inner workings of the extinction event.

“This unique site in North Dakota has provided a wealth of new and exciting information,” said Dr. Anton Oleinik, researcher at Florida Atlantic University.

“The field data collected at the site, after hard work to analyze it, has provided us with incredibly detailed new insight not only into what happened at the Cretaceous-Paleogene boundary, but also exactly when it happened. is produced. “

The unique structure and pattern of growth lines in fossil fish bones from the Tanis site showed that all of the fish examined died during the spring-summer growth phase.

Isotopic analysis of the growth lines provided independent confirmation of this, showing an annual oscillation that also ended during spring-summer growth.

The researchers further supported their findings by overlaying several additional data sources.

Examination of juvenile fossil fish was supported in part by advanced synchrotron scanning X-ray fluorescence (SRS-XRF), providing a new means of seasonal dating of the deposit.

Comparing the size of the youngest fish to modern growth rates has allowed scientists to predict how long after hatching the fish were buried.

Comparison with known modern spawning seasons allowed them to deduce which seasonal range was represented by the deposit at Tanis – from spring to summer, as the bones indicate.

“The beauty of any great discovery like this is that it is a chance to give back to the scientific community and to the world,” said Dr DePalma.

“It not only answers important questions, but also sparks new minds to move forward and achieve. “

The study was published in the journal Scientific reports.

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RA DePalma et al. 2021. Seasonal calibration of the Chicxulub impact event at the end of the Cretaceous period. Scientific representative 11, 23704; doi: 10.1038 / s41598-021-03232-9

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