Radioactive Dating Topic: Geologic Time (middle/high school chemistry)

Transcription

1 Radioactive Dating Topic: Geologic Time (middle/high school chemistry) by Lodge

2 Radioactive Dating Did ya ever find a rock and want to know the date That it was formed, within a number of years would you say...hey! Hey sedimentary rock I ll find your relative age By using superposition your covered older days Lava extrusion looks young Though the intrusions are igneous son I m feeling older - compared to some Chorus: Get absolute, with radioactive dating Wasting away, unstable old potassium fades Well, here s argon to take its place A half life, measure changes in the composition It s old, right...a billion years for only half to decay The stable elements will show the way (argon and nitrogen will show the way) With deposition, sediments they settle on the ground While the pesky erosion comes and washes out A layer of rock rock record gets swept away Causing geologic unconformity We find the age of what s left Using ammonites our global pets 65 to 500 million years for them to connect Carbon 14 decays to nitrogen And has a half life over 5,000 years it s used to date things, much like potassium but younger fossils are the dated ones here cause that s carbon s career

3 Student Lyric Guide

4 Name: Geologic Time Radioactive Dating Did ya ever find a rock and want to know the date That it was formed, within a number of years would you say hey! What is the name given to the scientist that studies rocks? Hey sedimentary rock I ll find your relative age What is one way to express the age of a rock? Define relative age: Describe your relative age in comparison to 2 family members. In what type of rock do fossils form? Why won t a fossil form in igneous rock?

5 By using superposition your covered older days How does sedimentary rock form? What is stated by the law of superposition? Where are the oldest rock layers in the Grand Canyon found? Lava extrusion looks young What is a lava extrusion? How is a lava extrusion used to determine age of rock layers? Though the intrusions are igneous son

6 What is an igneous intrusion? I m feeling older - compared to some How is an igneous intrusion used to determine age of rock layers? Get absolute, with radioactive dating The exact age of a rock is called the age of the rock. What is an element? Most elements are stable / unstable under normal conditions. Radioactive elements are stable / unstable under normal conditions. What is radioactive decay? Wasting away, unstable old potassium fades One common type of radioactive element is

7 Well, here s argon to take its place Potassium decays to form the element A half life, measure changes in the composition What is an element s half life? The rate of decay of a radioactive element is constant / changes. It s old, right A billion years for only half to decay What is the half life of postassium-40? What percentage of the potassium-40 would be left after 3 half lives? ½ * ½ * ½ = How can scientists use radioactive decay to determine absolute age of a rock?

8 The stable elements will show the way (argon and nitrogen will show the way) What is another example of elements used in radioactive decay? Unstable element: Stable element: With deposition, sediments they settle on the ground Define deposition: While the pesky erosion comes and washes out Define erosion: A layer of rock rock record gets swept away Causing geologic unconformity What is a geologic uncomformity? We find the age of what s left Using ammonites our global pets What is an ammonite? What is an index fossil? 65 to 500 million years for them to connect

9 When were ammonites present in the geologic record? How can scientists use ammonites to date rock layers? Carbon 14 decays to nitrogen What is another example of a radioactively decaying pair of elements? And has a half life over 5,000 years What is the half life of carbon-14? it s used to date things, much like potassium but younger fossils are the dated ones here cause that s carbon s career Why can carbon-14 dating only be used to date young fossils?

10 Teacher Key

11 Name: KEY Radioactive Dating Did ya ever find a rock and want to know the date That it was formed, within a number of years would you say...hey! What is the name given to the scientist that studies rocks? Geologist Hey sedimentary rock I ll find your relative age What is one way to express the age of a rock? Relative Age Define relative age: Age of a rock as it compares to the ages of other rocks Describe your relative age in comparison to 2 family members. I am older than my brother, but younger than my mom In what type of rock do fossils form? Sedimentary rock Why won t a fossil form in igneous rock? Igneous rocks are formed by magma By using superposition your covered older days How does sedimentary rock form? Forms when a layers of sediment over time hardens and forms rock What is stated by the law of superposition? In horizontal sedimentary rock layers, the oldest layer is on the bottom Each higher layer is younger than the layers below it Where are the oldest rock layers in the Grand Canyon found? At the bottom Lava extrusion looks young What is a lava extrusion?

12 It s lava that hardens on the surface of earth How is a lava extrusion used to determine age of rock layers? The extrusion is always younger than the layers below it Though the intrusions are igneous son What is an igneous intrusion? When magma pushes into bodies of rocks. It may cool and harden. The cool hardened magma is called an igneous intrusion. Magma that seeps into rocks and hardens I m feeling older - compared to some How is an igneous intrusion used to determine age of rock layers? Intrusion is always younger than the rock layers around it and beneath it. Get absolute, with radioactive dating The exact age of a rock is called the age of the rock. Absolute age What is an element? Pure substance that cannot be broken down into other substances by chemical or physical means Most elements are stable / unstable under normal conditions. Stable Radioactive elements are stable / unstable under normal conditions. Unstable What is radioactive decay? Over time, the atoms of one element break down to form atoms of another element Wasting away, unstable old potassium fades One common type of radioactive element is Potassium Well, here s argon to take its place

13 Potassium decays to form the element Argon A half life, measure changes in the composition What is an element s half life? The time it takes for ½ of the radioactive atoms to decay The rate of decay of a radioactive element is constant / changes. Constant It s old, right...a billion years for only half to decay What is the half life of postassium-40? 1.3 billion years What percentage of the potassium-40 would be left after 3 half lives? 1 2 * 1 2 * 1 2 = 1/8 = 12.5% How can scientists use radioactive decay to determine absolute age of a rock? They first determine the amount of a radioactive element in a rock. Then they compare that amount with the amount of the stable element into which the radioactive element decays. The stable elements will show the way (argon and nitrogen will show the way) List two examples of stable elements produced from radioactive decay. 1. Argon 2. Nitrogen What is another example of elements used in radioactive decay? Unstable element: Stable element: With deposition, sediments they settle on the ground

14 Define deposition: when sediment settles on the ground While the pesky erosion comes and washes out Define erosion: when water washes away sediments A layer of rock rock record gets swept away Causing geologic unconformity What is a geologic uncomformity? When water washes away a top layer of rock. New sediment settles on top making relative dating very difficult. We find the age of what s left Using ammonites our global pets What is an ammonite? A group of hard shelled animals that lived during a specific time period. They are an index fossil. What is an index fossil? A fossil that helps geologists match rock layer. It has to be widely distributed around the globe and it represents a type of organism that existed briefly. 65 to 500 million years for them to connect When were ammonites present in the geologic record? From 500 million years ago to 65 million years ago How can scientists use ammonites to date rock layers? They use them to match up rock layers that may be far apart. Carbon 14 decays to nitrogen What is another example of a radioactively decaying pair of elements? Carbon 14 Nitrogen And has a half life over 5,000 years What is the half life of carbon-14?

15 5,730 years it s used to date things, much like potassium but younger fossils are the dated ones here cause that s carbon s career Why can carbon-14 dating only be used to date young fossils? It has a very short half-life. It will be decay very quickly.

16 Music Video Extension Activity 1. Hand out or project the lyrics and read them out loud and discuss their meaning 2. Play the song for the students, multiple times, encouraging them to sing along 3. Use the student lyric guide in place of, or to supplement class notes 4. Allow students class time, in small groups, to act out a portion of the song 5. Film the student groups singing/acting out the song