1. In 1896, French scientists named Marie and Pierre Curie heard about experiments that had been done by another scientist, Henri Becquerel (bek uh REL). Becquerel had shown that by placing some uranium salt on a photographic plate, covered with black paper, the plate would be affected as if light had fallen on it. The effect is produced by special rays which are emitted by the uranium salt…. My determinations showed that the emission of the rays is an atomic property of the uranium. Marie Curie later described what happened: The property that Becquerel and the Curies discovered was called radioactivity. Today, radioactivity is used for many purposes—including finding the age of rocks! What did Marie curie discover about radioactivity? What does the discovery of the radioactivity tell you how scientists work together? Bellwork

2. Lesson 4: Radioactive Dating

4. Some elements decay, or break down, over time, releasing particles and energy. This process is called radioactive decay, and the elements are considered to be radioactive. During radioactive decay, the atoms of one element break down to form atoms of another element.

5. Radioactive Dating Half-Life The half-life of a radioactive element is the amount of time it takes for half of the radioactive atoms to decay. What pattern do you see in the graph? 6.25 %

6. The half-life of a radioactive element is the time it takes for half of the radioactive atoms to decay. The rate of decay of each radioactive element never changes.

7. Radioactive elements in igneous rocks decay over time into other elements. This slowly changes the composition of the rock. Geologists use radioactive dating to determine the absolute ages of rocks. In radioactive dating, scientists 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. They calculate the age of the rock using this information and the half-life of the element.

8. Elements Used in Radioactive Dating Radioactive Dating

9. Some elements used by scientists in radioactive dating include potassium-40 and carbon-14. Potassium-40 has a long half-life, which is useful in dating the most ancient rocks. All plants and animals contain some carbon-14, which decays after the organism dies. Scientists measure the amounts of carbon-14 to determine the age of a rock sample

10. To determine Earth’s age, scientists use radioactive dating and evidence from rocks on Earth and the moon. Using radioactive dating, Earth rocks are estimated to be between 3.8 and 4.28 billion years old. However, Earth rocks have changed over time due to the processes of plate tectonics and erosion. Moon rocks, fortunately, have not changed over time. According to one theory, scientists infer that the moon formed when another object collided with Earth. Since the moon came from Earth, the moon is about the same age as Earth. Radioactive dating estimates moon rocks to be 4.6 billion years old. Scientists estimate that Earth is about the same age.

11. Radioactive Dating Formation of the Moon According to one theory, a planet-sized object struck Earth. Material from the object and material from Earth were knocked into orbit around Earth. Gravity pulled the material together to form the moon. How do moon rocks help scientist estimate the age or Earth?