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Radioactive Dating

• Radioactive decay is the process by which unstable atoms release particles and energy in an effort to become stable.

1b How does the composition of a rock containing a radioactive element change over time?
• The amount of the radioactive element decreases.
• The amount of the stable element increases.

How is the rate of radioactive decay like the ticking of a clock?
• The rate of decay is constant – it never changes. It doesn’t speed up or slow down.

What method do geologists use to determine the absolute age of a rock?
• Geologists use radioactive dating to determine the absolute age of igneous rock.

Why is it difficult to determine the absolute age of sedimentary rock?
• The particles in sedimentary rock are made up of substances of different ages.

• A geologist finds a fossil in a layer of sedimentary rock that lies in between two igneous extrusions. How could the geologist determine the age of the fossil?
• The scientist could use radioactive dating to find the ages of the two igneous extrusions.
The age of the sedimentary rock would be somewhere in between the two ages.

• What percentage of a radioactive element will remain after 7 half lives?
• ½ x ½ x ½ x ½ x ½ x ½ x ½
• 1/128
• .0078125
• .78125%