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 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.
2 Radioactive Decay Rocks are a form of matter Atoms- tiny particles that make up all matterElement- 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 DecayRadioactive Decay- Over time unstable elements break down, or decay, by releasing particles and energy- these unstable elements are said to be radioactiveKey Concept- During the process of radioactive decay, the atoms of one element break down to form atoms of another element.
4 Radioactive DecayDuring radioactive decay, a “parent” atom releases energy and particles as it changes to a new kind of atom, a “daughter” atom.
5 Radioactive 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
6 Radioactive DecayAs the radioactive element in the rock decays it changes into another elementComposition changes slowly over timeAmount of radioactive element goes down and amount of new element goes up
7 Radioactive 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
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?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.Earth’s ever changing processes makes it difficult for scientists to determine Earth’s absolute ageRadioactive dating shows that the oldest rocks found on Earth are about 4.0 billion years oldThe oldest fossils of living things are about 3.5 billion years
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