Geologists rewrite textbooks with new insights from Grand Canyon’s Cambrian rocks

Since shortly after our planet formed, Earth’s 4.6 billion year history has been dominated by single-celled life. About 500 million years ago, a dramatic event called the Cambrian “explosion” occurred, during which an incredible diversity of life forms was left behind in the rock record. These fossils contained the major groups of diverse animals that evolved into the animal groups still living today (including humans).

A recent paper by UNM researchers and an expanded collaborative team is featured as a featured scientific article in the November 2024 issue of GSA Today titled “The Cambrian of the Grand Canyon: Refining the Classic Stratigraphic Model” has been.

“The Tonto Group of the Grand Canyon contains a treasure trove of sedimentary layers and fossils that record the Cambrian explosion approximately 500 million years ago. At this time, the first hard-shelled animals rapidly proliferated. “Rising sea levels have enveloped the continent with new marine life,” Carroll said. Mr. Deller is a professor at Utah State University.

Deller is the lead author, UNM adjunct professor and paleontologist Fred Sandberg is the co-first author, UNM Distinguished Professor Karl Carlstrom and Laurie Crossey, and James of the Denver Museum of Natural Science・Includes Mr. Hagadorn, Mark Schmitz of Boise State University, and Steve. Rowland of the University of Nevada, Las Vegas.

In addition to research advances, this paper includes geoscience education that builds on the classic model of ocean transgression (the advancement of oceans across continents) developed 50 years ago in the same rock by Eddie McKee. Progress is also described. The Mackie model, which is taught to many geology students around the world, assumes that depositional environments become progressively deeper and gradually change.

“Our new model for the deposition of the Tonto Group is more nuanced, accounting for a mix of marine and non-marine environments, breakage and unconformity when sediment is not being deposited, and a much faster evolutionary tempo. “It shows,” Karlstrom said. “Now more than ever, the Tonto Group of the Grand Canyon remains one of the most important Cambrian-type sections in the world due to its complete exposure.”

“Our findings remind us that science is a process,” Hagadorn said. “Our work at the Grand Canyon, one of the world’s most famous and beloved landscapes, connects people to this science in a very personal way.”

Additionally, advanced tools have provided new insights into the rate of rock deposition, providing clues about how marine species such as trilobites and other early animals diversified so rapidly.

“Our new tandem U-Pb dating method refines the precise chronology of transitions between each successive layer and trilobite biosphere,” Schmitz said, adding that “different trilobite species radially “We’re finding that they radiated and then went extinct at a very rapid rate.” -A million years, tempo. ”

This method involves crushing a sedimentary rock sample and separating hundreds of sand-sized zircon crystals deposited within the sediment. The U-Pb ratio of the particles is first obtained using a preliminary method for rapid dating, and then the most recent particles are precisely dated using more sophisticated (and accurate) laboratory methods. will be done.

Professor Crossy said, “It is difficult to determine the age of sedimentary rocks, but the age of the sediment and the fossils buried within it must be younger than the age of the youngest grain, so if there are many ages, it is possible to determine the age of the sediment. We can put it all together.”

Professor Deller said that compared to McKee’s model, the team’s new model provides an important pathway for both students and researchers to gain a deeper understanding of the Cambrian Explosion.

“From the 500-meter-thick geological formations of the Tonto Group, we are learning about the effects of sea level rise and devastating tropical storms, perhaps more powerful than today’s devastating hurricanes. in the world, It occurred during a time when there was no ice on Earth, when the temperatures were so high that sea levels were so high that deposits like the Tonto Group were deposited on top of most continents, creating a habitat for animals. Diversity has expanded rapidly on the planet.