Burying whatever lies between the layers this is how

This preview shows page 25 - 28 out of 47 pages.

burying whatever lies between the layers. This is how fossils typically form. Newest layers of rock are closer to the surface; older rocks are at the bottom of the layers. Index fossils in known distinctive layers aid scientists in the process of relative dating, where they can place fossils within certain rock layers in order according to time. Index fossils need to be easily recognizable and found in only a few rock layers that exist in many places. Radiometric dating is a much more specific dating procedure that aims to give the ab- solute age of a rock or fossil. Using radioactive isotopes, which decay at a steady rate, scientists can find the age in years of a sample. This technique takes advantage of the fact that different radioactive isotopes have different half-lives. GEOLOGIC TIME SCALE Scientists have made a geologic time scale that shows the basic divisions of the history of Earth. This is shown at the top of page 453. Note that the major divisions are called eons, eras, and periods . The chart will indicate the time frame for each period. It’s interesting to think about the scale as a clock as pictured on page 454. Notice that the Precambrian time had the longest span in Earth’s history so far. The specific details about each of the periods are located on pages 466–469. You should familiarize yourself with the details covered on these pages. © PENN FOSTER, INC. 2015 PAGE 325 BIOLOGY Lesson 3 Access to explore the conditions of Earth through time. You’ll need to use Google Chrome or Firefox to view this website.
LIFE ON A CHANGING PLANET There are different divisions of time for a reason: the planet isn’t stagnant. Therefore, any changes (physical or biological) can result in major effects on the life during the time of the change. Some of these changes include new land formations and movement of plates that resulted in a redistribution of organisms and natural disasters, such as earthquakes. Climate change and damaging objects from space have also affected life during Earth’s history. Organisms and their processes have also affected the life that comes next. For example, once oxygen-producing organisms began to arise, they paved the way for oxygen-dependent organisms to exist. Organisms are an integral part of the conditions of land, water, and atmosphere locations. Complete questions 1–7 on page 455. Click here to check your answers. CHAPTER MYSTERY Complete question 8 in the “Check Understanding” section on page 455. Be sure to review the ways in which events in history have been dated. © PENN FOSTER, INC. 2015 PAGE 326 BIOLOGY Lesson 3 ASSIGNMENT 12: THE FOSSIL RECORD REFLECT AND RESPOND
ASSIGNMENT 13 PATTERNS AND PROCESSES OF EVOLUTION Read this section in your study guide. Then, read Section 19.2 of Chapter 19 in your textbook. SPECIATION AND EXTINCTION Through studying the fossil record and the geological time scale, you’ve learned that new species come about and some even go extinct. Over 99 percent of the species that have ever lived have actually gone extinct. The patterns that help explain why this happens are referred to as

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture