8.3 Radioactive Dating 8.3 Radioactive Dating 7.4.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.
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8.3 Radioactive Dating 7.4.d Students know that evidence from geologic layers and radioactive dating indicates Earth is approximately 4.6 billion years.
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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
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