Astronomy 2021A/B Chapter Notes - Chapter 4: Van Allen Radiation Belt, Oceanic Trench, Outer Core

• School: Western University
• Department: Astronomy
• Course: Astronomy 2021A/B
• Professor: Alyssa Gilbert

Document Summary

4. 2 reconstructing the history of earth and life. Sedimentary strata: sedimentary rock is particularly important to our study of earth"s history for two reasons, most fossils are found in sedimentary rock, sedimentray rock forms in a way that tends to produce a record of time. However, this isotope is not the final daughter of uranium-238, because thorium-234 is also radioactive. Laboratory measurements show that this decay process has a half-life of 1. 25 billion years. Suppose a small piece of rock contained 1 microgram of potassium-40 and no argon-40 when it formed (solidified) long ago. Half of this remaining potassium-40 had then decayed by the end of the next. 1. 25 billion years, so after billion years, the rock contained microgram of potassium-40 and microgram of argon-40. After three half-lives, or 3. 75 billion years, only microgram of potassium-40 remained, while microgram had become argon-40. The essence of radiometric dating: potassium-40 example shows the essence of radiometric dating -