Arizona rock will help solve mysteries of the Triassic 

A huge rock core from the Petrified Forest in Arizona is providing new insight into how our planet was impacted by natural disasters during the Triassic Period. Analysis of the quarter-mile rock core will help scientists understand how Earth’s ecosystems evolved and what led to the end-Triassic extinction around 201 million years ago.

The Triassic is characterized by a number of catastrophic events, including at least three impacts by enormous asteroids, widespread volcanic eruptions, and tectonic movement that tore apart the supercontinent Pangea.

During this chaotic time period, a large number of plants and animals vanished, including some of the long-snouted and armored reptiles that ruled Pangea. The exact cause of the extinction event has remained a mystery.

The geological record in the rock core contains a continuous stretch of Earth’s history from 225 million to 209 million years ago. The timeline provides an opportunity for scientists to investigate abrupt environmental changes during the peak of the Late Triassic.

Cornelia Rasmussen is a postdoctoral researcher at the University of Texas Institute for Geophysics (UTIG), who led the core dating analysis.

“The core lets us wind the clock back 225 million years when Petrified Forest National Park was a tropical hothouse populated by crocodile-like reptiles and turkey-size early dinosaurs,” said Rasmussen.

“We can now begin to interpret changes in the fossil record, such as whether changes in the plant and animal world at the time were caused by an asteroid impact or rather by slow geographic changes of the supercontinent drifting apart.”

Dr. Adam Marsh is a paleontologist at Petrified Forest National Park. He explained that despite a rich collection of fossils from the period in North America, until now there was little information on the Late Triassic’s timeline because most of what scientists knew came from studying outcrops of exposed rock pushed to the surface by tectonic movements.

“Outcrops are like broken pieces of a puzzle,” said Dr. Marsh.”It is incredibly difficult to piece together a continuous timeline from their exposed and weathered faces.”

The new core contains every rock layer in the order it was deposited, which means the layers can be matched with the fossil and climate record.

According to Rasmussen, the analysis of the core produced two slightly different stories. The first scenario suggests that changes across Triassic species were not connected to any single catastrophic event, but were  simply due to the natural course of evolution. The second scenario shows a correlation between changes in the fossil record and a powerful asteroid impact, which left behind a crater in Canada over 62 miles wide.

Dr. Marsh said the findings are just part of the process to reach the truth. “The two age models are not problematic and will help guide future studies.”

The study is published in the journal GSA Bulletin.

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By Chrissy Sexton, Earth.com Staff Writer