8.3 radioactive dating 7.4.d students know that evidence from geologic layers and radioactive dating...
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8.3 Radioactive Dating8.3 Radioactive Dating7.4.d Students know that evidence from geologic layers and radioactive dating indicates Earth is approximately 4.6 billion years old and that life on this planet has existed for more than 3 billion years.
Radioactive DecayRadioactive DecayRocks are a form
of matterAtoms- tiny
particles that make up all matter
Element- any substance that cannot be broken down into simpler substances (examples: carbon, oxygen, iron, lead)
Most elements are stable- do not change under normal conditions
Radioactive DecayRadioactive DecayRadioactive Decay-
Over time unstable elements break down, or decay, by releasing particles and energy- these unstable elements are said to be radioactive
Key Concept- During the process of radioactive decay, the atoms of one element break down to form atoms of another element.
Radioactive DecayRadioactive Decay
During radioactive decay, a “parent” atom releases energy and particles as it changes to a new kind of atom, a “daughter” atom.
Radioactive DecayRadioactive DecayRadioactive elements happen
naturally in igneous rocksScientists use the rate of decay to
calculate the rock’s age“Birthday” for an igneous rock is
when it first hardens to become rock
Radioactive DecayRadioactive Decay
As the radioactive element in the rock decays it changes into another element
Composition changes slowly over timeAmount of radioactive element goes
down and amount of new element goes up
Radioactive DecayRadioactive DecayRate of decay is constant for each radioactive
elementScientists can measure the rate of decay
experimentallyHalf-life- the time it takes for half of the
radioactive atoms to decay
Determining Absolute Determining Absolute AgesAges
Key Concept- Radioactive dating is used to determine the absolute ages of rocks.
Determining Absolute Determining Absolute AgesAges
Table lists several common radioactive elements and their half-lives.
Carbon-14 has a half-life of 5,730 years and is useful in dating plants and animals that lived up to about 50,000 years ago.
Potassium-40 decays to a stable argon-40 and has a half-life of 1.3 billion years. It is useful in dating most ancient rocks because of its long half-life.
Example is the decay
of Potassium-40 to
Argon-40
Determining Absolute Determining Absolute AgesAges In radioactive dating
first measure the amount of radioactive element in a rock (“parent” element)
Then measure the amount of stable element that the unstable radioactive element decays into (“daughter” element)
By calculating the ratio of radioactive element to the stable element you can determine the age of the rock
How Old is Earth?How Old is Earth?
Earth’s ever changing processes makes it difficult for scientists to determine Earth’s absolute age
Radioactive dating shows that the oldest rocks found on Earth are about 4.0 billion years old
The oldest fossils of living things are about 3.5 billion years
Key Concept- Radioactive dating shows that the oldest moon rocks are about 4.6 billion years old. Scientists infer that Earth is only a little older than those moon rocks– roughly 4.6 billion years old.
More on Radioactive More on Radioactive DatingDating
Click the PHSchool.com button for an activity about radioactive dating.
Video: Greatest Discoveries with Bill Nye: Rocks of Ages
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