Post by jonsdigs on Mar 6, 2008 19:45:30 GMT -5
Grand Canyon Might Be Older Than Thought
By Joel Achenbach
Washington Post Staff Writer
Thursday, March 6, 2008; 2:36 PM
Visitors to the Grand Canyon always want to know: How old is it?
Park rangers are instructed to tell them that the canyon has been carved by the Colorado River for the past 5 million or 6 million years.
Cave mammillaries coat cave walls below but near the water table. A cross section of broken mammillaries (m) and exposure of underlying bedrock (b) from site 6 (Tsean Bida) are shown. The unbroken form of this speleothem type (white arrows) indicates a subaqueous origin.
(Image courtesy of Science/AAAS)
...Polyak's research paired new lab techniques with intrepid field work. Researchers had to climb canyon walls to reach ancient caves containing crucial evidence of the canyon's history. The scientists examined mammillaries, also known as cave clouds, which are rounded rock structures that tend to form underwater near the top of a water table.
In the canyon, these rocks also contain abundant amounts of uranium. In recent years scientists have improved techniques for dating rocks based on the predictable decay of uranium into lead.
Polyak and geologist Carol Hill suggested the research project to geochemist Yemane Asmerom, Polyak's boss at the University of New Mexico: Why not use the new lab techniques to measure the ages of the mamillaries? That ought to tell the story, Polyak reasoned, of how the river gradually cut through the plateau and lowered the water table...
Full Story
By Joel Achenbach
Washington Post Staff Writer
Thursday, March 6, 2008; 2:36 PM
Visitors to the Grand Canyon always want to know: How old is it?
Park rangers are instructed to tell them that the canyon has been carved by the Colorado River for the past 5 million or 6 million years.
Cave mammillaries coat cave walls below but near the water table. A cross section of broken mammillaries (m) and exposure of underlying bedrock (b) from site 6 (Tsean Bida) are shown. The unbroken form of this speleothem type (white arrows) indicates a subaqueous origin.
(Image courtesy of Science/AAAS)
...Polyak's research paired new lab techniques with intrepid field work. Researchers had to climb canyon walls to reach ancient caves containing crucial evidence of the canyon's history. The scientists examined mammillaries, also known as cave clouds, which are rounded rock structures that tend to form underwater near the top of a water table.
In the canyon, these rocks also contain abundant amounts of uranium. In recent years scientists have improved techniques for dating rocks based on the predictable decay of uranium into lead.
Polyak and geologist Carol Hill suggested the research project to geochemist Yemane Asmerom, Polyak's boss at the University of New Mexico: Why not use the new lab techniques to measure the ages of the mamillaries? That ought to tell the story, Polyak reasoned, of how the river gradually cut through the plateau and lowered the water table...
Full Story