Assignment 4
Dating:  Steno's Laws, Radioactivity, and Geologic Time
 

Adapted from:  What On Earth Is Evolution?  The Geological Perspective of Teaching Evolutionary Biology Effectively, by Abour Cherif, Jerry Adams, and John Loehr (2000) 

   

Goals:

  1. To define and distinguish between relative and radiometric methods of dating.
  2. To understand the types of dating information provided by the relative positions of geological strata.
  3. To apply principles of radioactive decay and Steno's Laws to problems about the age of organisms.
  4. To understand how information obtained through dating is important to understanding the theory of evolution.

Objectives: Students will be able to

  • Explain Steno's Laws and apply that knowledge to determine the relative ages of geological strata and fossils therein,
  • Know the benefits and limitations of relative and radiometric dating methods, and
  • Solve problems about ages of biotic and abiotic materials using principles pertaining to geological strata and radioative decay.

 

In Assignment 3, we began exploring the age of the Earth.  You worked in small groups and as a class to complete the "If Scientists Think. . ." table.  Through presentation and discussion of individual ideas, the class reached agreements as to the best way to complete each of the prompts.  Today's assignment will allow you to compare and contrast your ideas to some of the actual methods scientists used to develop an estimation of the age of the Earth.

Following this introduction, there are several links to different sites concerning the methods scientists use to assist them in estimating the age of the Earth.  You will investigate Steno's Laws, radiometric dating, and then visit an interactive site that will help you better understand how to tell time - with geology! 

Because this assignment is linked with your work in Assignment 3, you will have "If Scientists Think. . ." returned to you.  As you proceed through Assignment 4, be sure to compare your answers from "If Scientists Think. . ." to the actual methods scientists use to estimate the age of prehistoric objects. 


 

PART A.  RELATIVE DATING: STENO'S LAWS

Before scientists had modern technology to assist them in their research, they had to use their power of observation to infer the relative ages of the rocks they were studying.  The process of Relative Dating was established by Nicholaus Steno in the 1600's.  Steno developed a set of Laws (Steno's Laws) to help explain his method of inferring the ages of geological structures.  These laws are a set of hypotheses that the scientific community accepts as a starting basis without absolute proof.  While this may sound questionable at first, keep in mind that we also accept the Law of Gravity with out direct proof.

Visit the following site and read about each of Steno's laws (principles). Keep these principles in mind as you progress through the rest of the activities in this assignment.  It would benefit your understanding of this material if you studied the rest of this website on your own, but it is not required for class.  

Steno's Laws

Click Here to Learn About Steno's Laws


   

PART B.  RADIOMETRIC DATING

Now that you have discovered the method that scientists originally used to date geological features, you may be questioning the accuracy of this dating method.  After all, it is possible that rock layers can be disturbed, overturned, and altered in both natural and unnatural ways.  Who's to say that the rocks a particular scientist is studying have not been displaced from their original positions?  In addition to the "relative" uncertainty that the geological features of an area have retained their historical integrity, there is another problem associated with relative dating.  By looking at layers of rocks, scientists can tell which layers are older or newer than others; however, they can not tell exactly how old these layers are.  Technology has progressed phenomenally since Steno's time.  Scientists have developed technology that can accurately date rocks using radioactive materials which are fixed into the rocks as they form from sediments.  This dating technique is known as radiometric dating.  You have probably heard of mummies that have been dated with the Carbon-14 method.  The Carbon-14 method measures the amount of radioactive carbon-14 in a previously living artifact.  From this information, scientists can accurately infer the age of the test material.   

Continue to the Radiometric Dating portion of this assignment through use of a virtual web site.  Answer the questions about each aspect of radiometric dating as you move through the various exercises of the Radiometric Dating Lab.   If you have an incorrect answer be sure to figure out why that answer was wrong and what is the correct answer.  This is a relatively long activity so stay focused on your work.  Let your TA or Professor see your Certificate of Completion once you reach that screen at the end of the activity.  

Radiometric Dating

Click here for the Radiometric Dating Lab

  
 

PART C.  GEOLOGIC TIME

To obtain further practice with the concepts of Steno's laws and geologic dating, work through the Understanding Geological Time section of this assignment.  This portion of the assignment is an interactive web site that allows you to apply what you have learned and to learn more about how scientists tell time with geology. The web site is simple, especially at the begnining, yet allows you to visualize relationships among the main concepts you have been studying. The site ends with a short quiz - you should get a perfect score if you understand Web Assisgnment 4.  When you enter the site, in the top left corner you will see the words "Student Start."  Click there to begin.  

Understanding Geologic Time

Click Here to Learn More About Understanding Geologic Time