A sandstone is found to overlie a shale. The shale contains a volcanic ash layer that has been radiometrically dated to 84 million years ago. Both the shale and the sandstone are cut by a pluton of gabbro that has been dated to 60 million years old
How old is the sandstone layer?
A) between 84 and 60 million years old
B) older than 84 millions years old
C) younger than 60 million years old
D) more information is needed to constrain the age
Answer: A
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