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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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Presentation on theme: "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."— Presentation transcript:

1 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.

2 Radioactive Decay Rocks are a form of matter Atoms- 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

3 Radioactive Decay Radioactive 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.

4 Radioactive Decay During radioactive decay, a parent atom releases energy and particles as it changes to a new kind of atom, a daughter atom.

5 Radioactive Decay Radioactive elements happen naturally in igneous rocks Scientists use the rate of decay to calculate the rocks age Birthday for an igneous rock is when it first hardens to become rock

6 Radioactive Decay As the radioactive element in the rock decays it changes into another element Composition changes slowly over time Amount of radioactive element goes down and amount of new element goes up

7 Radioactive Decay Rate of decay is constant for each radioactive element Scientists can measure the rate of decay experimentally Half-life- the time it takes for half of the radioactive atoms to decay

8 Determining Absolute Ages Key Concept- Radioactive dating is used to determine the absolute ages of rocks.

9 Determining Absolute Ages 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

10 Determining Absolute Ages 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

11 How Old is Earth? Earths ever changing processes makes it difficult for scientists to determine Earths 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.

12 More on Radioactive Dating Click the PHSchool.com button for an activity about radioactive dating. Video: Greatest Discoveries with Bill Nye: Rocks of Ages


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