The skull of a phytosaurus, an extinct reptile that lived during the Late Triassic in what is now Petrified Forest National Park, Arizona. Analysis of a rock core led by the University of Texas Institute of Geophysics is helping scientists reconstruct a more accurate timeline of the geological period in which this creature lived. Credit: National Park Service
A rocky core in Petrified Forest National Park, Arizona, has given scientists a powerful new tool to understand how catastrophic events shaped Earth’s ecosystems before the dinosaurs emerged.
The quarter-mile core is an important part of the Triassic Period when life on Earth suffered a series of cataclysmic events: our planet was hit at least three times by mountain-sized asteroids, volcano chains exploded to choke the sky with greenhouse gases, and tectonic movement tore through the only supercontinent on Earth, Pangea.
A close-up of the quarter-mile rocky core whose total length represents a continuous geological record from 225 million to 209 million years ago. Cornelia Rasmussen, a postdoctoral researcher at the University of Texas Institute of Geophysics, has worked at the core since it was drilled in the Petrified Forest National Park in 2013. Credit: Cornelia Rasmussen
Amid the chaos, many plants and animals, including some of the long-armed, snout-lined reptiles that ruled Pangea throughout the Triassic, disappeared in a possible shake-up of life on Earth that scientists have not yet explained.
The study, published today (July 20, 2020) in GSA Newsletter, offers scientists a basis to explain changes in the fossil record and determine how these events may have shaped life on Earth.
By determining the age of the rock’s core, the researchers were able to reconstruct a continuous and uninterrupted stretch of Earth’s history from 225 million to 209 million years ago. The timeline provides insight into what a geological dark age has been like and will help scientists investigate abrupt environmental changes since the late Triassic peak and how they affected plants and animals of the time.
Before the rock core recovered, most of what was known about the Late Triassic came from searching for signs of the Chinle Formation on rocky outcrops like this, found throughout the Petrified Forest National Park. The rock layers that make up the formation were deposited during the Late Triassic Period. Credit: Randall Irmis / NHMU
“The core allows us to go back 225 million years when the Petrified Forest National Park was a tropical greenhouse populated by crocodile-like reptiles and early turkey-sized dinosaurs,” said Cornelia Rasmussen, a postdoctoral researcher at the Institute of Geophysics at the University of Texas. (UTIG), who led the analysis that determined the age of the nucleus.
“We can now begin to interpret the changes in the fossil record, as if the changes in the world of plants and animals at that time were caused by an asteroid impact or rather by slow geographic changes of the separating supercontinent “, said.
A close-up of the quarter-mile rocky core whose total length represents a continuous geological record from 225 million to 209 million years ago. Cornelia Rasmussen, a postdoctoral researcher at the University of Texas Institute of Geophysics, has worked at the core since it was drilled in the Petrified Forest National Park in 2013. Credit: Cornelia Rasmussen
Paleontologist Adam Marsh of Petrified Forest National Park said that despite a rich collection of period fossils in North America, until now there was little information on the Late Triassic timeline because most of what scientists knew came from from the study of exposed rock outcrops pushed to the surface by tectonic movements.
“The outcrops are like broken pieces of a puzzle,” said Marsh, who obtained his Ph.D. from the University of Texas at Austin Jackson School of Geosciences. “It is incredibly difficult to put together a continuous timeline of their exposed and worn faces.”
Marsh was not the author of the study, but is part of the largest scientific sampling project. UTIG is a unit of the Jackson School.
The core of the Petrified Forest National Park overcomes the problem of the broken puzzle by recovering each layer in the order in which it was deposited. Like tree rings, scientists can link those layers to the fossil and climate record.
The nucleus was recovered from the Petrified Forest National Park in 2013 by the Colorado Plateau Coring Project. By analyzing the age of the nucleus, Cornelia Rasmussen, postdoctoral researcher at the University of Texas Institute of Geophysics, was able to create an accurate timeline that will help answer questions about life on Earth during the late Triassic peak. Credit: Randall Irmis / NHMU
To find the age of each layer, the researchers searched the core of the rock for small crystals of the mineral zircon, which are thrown into the sky during volcanic eruptions. Zircons are a date stamp for the sediments with which they are buried. The researchers then compared the age of the crystals to the traces of ancient magnetism stored in the rocks to help develop an accurate geological timeline.
However, geoscience is seldom that simple, and according to Rasmussen, analysis of the nucleus gave them two slightly different stories. One shows evidence that a jolt in the species might not be related to any catastrophic event and could simply be part of the ordinary course of gradual evolution. The other shows a possible correlation between the change in the fossil record and a powerful asteroid impact, which left a crater in Canada over 62 miles wide.
For Marsh, the different findings are only part of the process to reach the truth.
“The two age models are not problematic and will help guide future studies,” he said.
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Reference: July 20, 2020, GSA Newsletter.
The research is the latest outcome of the Colorado Plateau Coring Project. The core extraction research and project was funded by the National Science Foundation and the International Continental Drilling Program.
