Researchers Find Clues to Geological Dark Age in Ancient History

An example of rocky “outcrops” found throughout Petrified Forest National Park in Arizona. Before a new study, most of what was known about the Late Triassic period came from research conducted on these formations. (Randall Irmis/NHMU)

(CN) — Researchers studying underground rock samples from northern Arizona say they’ve discovered important clues to an early part of Earth’s ancient history, when the first dinosaurs and early crocodile-like reptiles roamed the planet.

In a study published Monday in the journal GSA Bulletin, a team led by the University of Texas Institute for Geophysics said an analysis of the core revealed previously unknown details about the Late Triassic Period, an era more than 200 million years ago that culminated in a series of massive comet strikes and the still-unexplained disappearance of many animals and plants.

The findings are an important first step toward solving that mystery, the researchers said.

“We have often these really great ideas and it’s lots of fun to think about, oh maybe this volcanic eruption caused the extinction of this and this, but if we don’t understand time, we can never verify it,” Cornelia Rasmussen, a postdoctoral fellow at the University of Texas and the study’s leather author, said in an interview.

Rasmussen and scientists from universities in Utah, California and other states analyzed the rock core samples from a digging expedition at Petrified Forest National Park in Arizona. The park’s name comes from its ancient fossilized forests that originally grew during the Triassic Period, but it’s home to a plethora of other fossils as well.

The geologic evidence in the core revealed new details about an era that has been previously murky to scientists. The researchers said their study will serve as a “foundation” to help fill the current gap in that scientific understanding and to paint a clear picture of the series of “cataclysmic” events that rocked the planet as the Triassic came to a close.

The skull of a phytosaur, an extinct, crocodile-like reptile that lived during the Late Triassic in what is now Petrified Forest National Park in Arizona. (National Park Service)

There are varying theories as to whether the disappearance of many animals and plants during this period was due to dramatic events, like the comets that scientists know hit the earth at the time, or due to slower events, like the breaking up of the early supercontinent Pangea or changes in the climate.

Monday’s study will allow scientists to begin sorting out which of those scenarios is more likely, Rasmussen said.

“We have for the first time now the opportunity to really create this continuous timeline,” she said.

The disappearance of animals and plants that happened during this early period were not as widespread as the later complete annihilation of the dinosaurs altogether. The dinosaurs that disappeared during the Late Triassic were also much smaller versions of the massive beasts we commonly think of today.

“It’s more like a family member dying, so the overall family is still there,” Rasmussen said of the early extinctions. “At this period, dinosaurs are still basically in their overall childhood, they’re more like turkey-sized little guys.”

The research team conducted the analysis by drilling down about a third of a mile into the ground at the national park, gathering samples from the rock’s core and later analyzing the samples at labs. The study was part of the broader Colorado Plateau Coring Project, an effort involving many scientists to better understand environmental changes to plants and animals throughout the entire Triassic Period.

Before Monday’s study, scientists studying the Late Triassic had mostly analyzed “outcrops” of rock at the national park that were pushed up to the earth’s surface by underground tectonic shifts.

“Outcrops are like broken pieces of a puzzle,” said Adam Marsh, a paleontologist at the park who was not directly involved in the new study, in a statement accompanying the study’s release. “It is incredibly difficult to piece together a continuous timeline from their exposed and weathered faces.”

The rock’s core is much more useful for reading back through the planet’s history, the researchers said, in the same way that scientists analyze tree rings to get a better understanding of long-term environmental changes.

Going forward, the researchers hope to further analyze the samples and conduct similar studies at different locations, though Rasmussen said where exactly they might travel next is still uncertain.

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