Rock sample gives clues into climate change
250 million years ago, the Earth was made up of a vast sea and one supercontinent. Over some 40 million years, during what’s known as the Triassic period, mountain-sized asteroids bombarded our planet at least three times, chains of volcanoes erupted and choked the sky with greenhouse gases and, toward the latter part of the period, tectonic movement tore apart Earth’s single supercontinent, Pangea.
Scientists have yet to understand how rapidly these chaotic events altered life on Earth. Now, a rock core from Petrified Forest National Park in Arizona has given scientists a new tool to understand how these catastrophic episodes shaped Earth’s ecosystems before the rise of the dinosaurs.
“Now we can learn more about geologic time,” said Cornelia Rasmussen, a postdoctoral researcher at the University of Texas Institute for Geophysics, who led the analysis that determined the age of the core. “Was this biotic turnover caused by the impact events or more gradual change?”
The sample was drilled for the researchers by a scientific drilling company. A rig similar to an oil rig extracted a quarter-mile sample beneath a parking lot at the national park.
The quarter-mile-long rock core spans some of the cataclysmic events that shaped the prehistoric world. For the first time, Rasmussen and a group of researchers were able to piece together a continuous stretch of Earth’s history from 225 million to 209 million years ago. The timeline will help scientists better understand the environmental changes that occurred during the Late Triassic period and how they affected the plants and animals of the time.
Previously, scientists only had glimpses of changes caused by chaotic moments during the Triassic period. A rich collection of fossils from the period have been collected throughout North America, but the fossils came from outcrops of exposed rock pushed to the surface by ancient tectonic movements and only provided pieces of the puzzle.
The Chinle Formation, those colorful hills that give the Painted Desert its name, was deposited over 200 million years ago during the Late Triassic period. Most of what used to be known about the Late Triassic period came from studying rocky outcrops on these formations, which are found throughout Petrified Forest National Park.
But the core, like tree rings, shows each geologic layer in the order it was deposited. Scientists can match those layers with the fossil and climate record.
“Evolutionary events that may appear very sudden just by looking at fossils were maybe actually very slow, but we can now start to resolve these questions with the records we have,” Rasmussen said.
To find the age of each layer, the researchers searched the rock core for tiny crystals of the mineral zircon, which are spewed during volcanic eruptions and provide a time stamp for the sediments with which they are buried.
In the Late Triassic period, what later became the Petrified National Forest was much closer to the equator and was one of the hottest and most humid places on Pangea. Long-snouted reptiles and turkey-sized early dinosaurs ruled the land. Carbon dioxide emissions, which today are driven primarily by human activity, filled the atmosphere as huge volcanoes erupted and seasonal wildfires burned extensively. Three huge meteors hit the earth, and their imprints remain preserved in what’s now Canada and France.
The apocalyptic time may seem familiar. The main difference is that climate-changing greenhouse gas emissions were caused naturally then, when the world looked much different and was all around much hotter.
“You have these big, altering events, and then overall you have a supercontinent, which would be excellent because we could go everywhere by train, but it also has effects on climate,” Rasmussen said. “You have stronger seasonality during that time, and the carbon cycle is a bit different because of this giant land mass, and volcanic eruptions turning the climate into a hothouse, which means we have much higher CO2 than we have today.”
The Triassic period was bookended by two mass extinctions, ultimately causing the huge crocodile-like creatures to go extinct while the smaller dinosaurs that once ambled the land evolved into the giant dinosaurs we think of today.
Still, the new study has allowed scientists to get one step closer to understanding how quickly the world changed back then. The only sure thing in how the study relates to climate change impacts now is that major changes in climate are likely to lead to mass extinction.