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How do they determine the continental crust's age?

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Zircons have to be present in really old rocks in order to estimate their age, using radiometric dating. The known decay rate of radioactive isotopes is used to compute the age of a particular sample. read more

But the age of the continental crust is going to vary based on where you measure it. For instance, the layers in the Grand Canyon are between 1.7 billion years old (The Vishnu Schist at the bottom) and about 250 million years old (the Kaibab Limestone at the top). read more

In other words, radiogenic isotopes can be used to calculate 'model ages' of crust formation, which represent the time since a crustal sample was separated from its mantle source. The concept of 'model age' has been widely used in crustal evolution studies for the last three decades. read more

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