Radioactive Dating (pages 323–326) 1. Explain what happens

Radioactive Dating
(pages 323–326)
1. Explain what happens
during radioactive decay.
2. Describe what can be
learned from radioactive
dating.
Radioactive Decay
(page 324)
1. Explain what happens
during radioactive decay.
Key Concept: During
radioactive decay, the
atoms of one element
break down to form
atoms of another
element.
Everything is made up of
one or more pure
substances. These pure
substances are called
elements.
Some elements break
down, or decay. When an
element decays, it
changes into another kind
of element. The process is
called radioactive decay.
Elements that
decay are
called
radioactive
elements.
Potassium-40
is an example.
Potassium-40
decays into
argon-40.
How fast an element decays
is given by its half-life. The
half-life is the time it takes
for half of a sample of an
element to decay. For
example, the half-life of
potassium-40 is 1.3 billion
years.
Determining Absolute
Ages (pages 325–326)
2. Describe what can be
learned from radioactive
dating.
Key Concept:
Geologists use
radioactive dating to
determine the
absolute ages of
rocks.
Scientists test rocks to
measure how much
radioactive decay has
happened. The more
decay that has
happened, the older the
rocks is.
This method of dating
rocks is called radioactive
dating. Using this method,
scientists can give rocks a
rough age in years. When
age is given in years, it is
called absolute age.
Suppose that half of the
potassium-40 in a rock has
decayed to argon-40. The
half-life of potassium-40 is
1.3 billion years, so the
rock is about 1.3 billion
years old.
Radioactive dating works
well for igneous rocks. But
this kind of dating does not
work well for sedimentary
rocks. This is because
sedimentary rocks are
made of rock particles of
different ages.