The combined uranium/thorium/helium dating of minerals from the bottom of the Grand Canyon in Arizona, the United States, indicates it was largely carved out by about 70 million years ago.
“The new research pushes back the conventionally accepted date for the formation of the Grand Canyon by more than 60 million years,” said Prof Rebecca Flowers of the University of Colorado at Boulder’s Department of Geological Sciences, a lead author of a paper reporting the results in the journal Science.
Prof Flowers and her colleague, Prof Kenneth Farley of California Institute of Technology, used the combined U–Th–4He–3He dating technique that exploits the radioactive decay of uranium and thorium atoms to helium atoms in a phosphate mineral known as apatite.
“The main thing this technique allows us to do is detect variations in the thermal structure at shallow levels of the Earth’s crust. Since these variations are in part induced by the topography of the region, we obtained dates that allowed us to constrain the timeframe when the Grand Canyon was incised,” Prof Flowers explained.
“The helium atoms were locked in the mineral grains as they cooled and moved closer to the surface during the carving of the Grand Canyon,” she said. “Temperature variations at shallow levels beneath the Earth’s surface are influenced by topography, and the thermal history recorded by the apatite grains allowed the team to infer how much time had passed since there was significant natural excavation of the Grand Canyon.”
“Our research implies that the Grand Canyon was directly carved to within a few hundred meters of its modern depth by about 70 million years ago,” Prof Flowers said.
Prof Flowers said there is significant controversy among scientists over the age and evolution of the Grand Canyon. A variety of data suggest that the Grand Canyon had a complicated history, and the entire modern canyon may not have been carved all at the same time. Different canyon segments may have evolved separately before coalescing into what visitors see today.
“Visited by more than 5 million people annually, the iconic canyon was likely carved in large part by an ancestral waterway of the Colorado River that was flowing in the opposite direction millions of years ago,” Prof Flowers said.
“An ancient Grand Canyon has important implications for understanding the evolution of landscapes, topography, hydrology and tectonics in the western U.S. and in mountain belts more generally,” Prof Flowers said.
Bibliographic information: RM Flowers, KA Farley. Apatite 4He/3He and (U-Th)/He Evidence for an Ancient Grand Canyon. Science, published online November 29, 2012; doi: 10.1126/science.1229390
Source link: https://www.sci.news/geology/article00753.html
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