1. Unit 5 – The Age of the Earth as Told by the Rocks

2. Before modern ___________, the age of the Earth was determined for many people by their governments or religious establishments In the ________, most people accepted the belief of the Church Archbishop James Ussher used the Bible to estimate the creation of the Earth on ____________________________

3. ________________, a Scottish physician and farmer, observed that changes in his farm were very slow, and decided that the Earth would need much more than 6000 years to form the way it is

4. Hutton proposed the _________________________________ the idea that the same forces that shape the Earth now have been shaping it for many years in the past

5. The sedimentary rocks in the Earth serve as a record keeper of ___________________ The layers of sedimentary rock, known as _____________, are like pages in a History book

6. The _________________________states that sedimentary strata build on top of each other as the sediments are deposited How each stratum compares to the others is called its ______________________

7. Sometimes the sedimentary rock layers move due to tectonic forces and change from their original position By studying the rock particles in the layers, scientists can determine whether a rock layer has changed or not

8. Any break or change in the rock record is called an ______________________

11. Determining the exact age of a rock, or its ________________, must be done with a technique called radiometric dating Isotopes of certain atoms are ____________________, which means they lose mass and energy from their nucleus

12. Each type of radioactive isotope decays at a very predictable rate in what is known as a _________________ A half-life is the length of time it takes for half of the radioactive isotopes to change into a stable form What are the half lives for… Uranium-238 Potassium-40 Rubidium-87

14. Carbon dating is used to determine the age of living things that have died no later than ____________________years ago Carbon-14 is a radioactive isotope that breaks down into carbon-12 with a half life of _____________ years

15. Sedimentary rock contains _____________ of organisms that tell us the history of life on the Earth The oldest fossils are nearly _______________ years old and are less complex than bacteria

16. Types of fossils

22. _________________are abundant fossils that help scientists determine the age of some rocks ______________ date back from 200-60 million years

23. _________________ date from 245 to 575 million years

24. __________________date from 145 to 65 million years