Age determinations from radioactive-isotope decay methods are usually performed on a mineral crystal. Assume that a rounded grain of feldspar is plucked from a sandstone, analyzed, and determined to be 200 million years old
What does this tell you about the age of the sandstone? What other methods can be used to determine when the sand in the sandstone was deposited?
What will be an ideal response?
We know that the crystal was formed 200 m.y. ago. This is the maximum age of the rock, and we can only say that the sandstone is less than 200 m.y. Analysis of the cementing agent can give us information about the minimum age of the rock. Fossil content can further refine the age, as well as determining the age of minerals in any igneous rocks that cross-cut the sandstone.
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At the 2009 Copenhagen climate conference,
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How did the decline of China during the 1800s affect the geopolitical structure of East Asia?
What will be an ideal response?