Pamela Gore, Georgia Perimeter College.
Focus Questions Key
Short discussion of radioactive dating and stratigraphic principles. Includes tables of common radioactive parent isotopes and their stable daughter products, and half lives of common radioactive isotopes. Geologic time , U. This online version of their informative booklet contains short, content explanations about relative time, major geologic time divisions, index fossils for use in age dating, radiometric dating and the age of the earth.
Age Dating, Educational Resources for K
Content information about absolute and relative dating methods used by the U. Radiometric dating , Wikipedia. Content information from on-line encyclopedia that explains various. An Equal Opportunity University. Contact the Webmaster for questions and comments. Last modified August 1, Geologists in the late 18th and early 19th century studied rock layers and the fossils in them to determine relative age.
William Smith was one of the most important scientists from this time who helped to develop knowledge of the succession of different fossils by studying their distribution through the sequence of sedimentary rocks in southern England. It wasn't until well into the 20th century that enough information had accumulated about the rate of radioactive decay that the age of rocks and fossils in number of years could be determined through radiometric age dating.
This activity on determining age of rocks and fossils is intended for 8th or 9th grade students.
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It is estimated to require four hours of class time, including approximately one hour total of occasional instruction and explanation from the teacher and two hours of group team and individual activities by the students, plus one hour of discussion among students within the working groups.
Explore this link for additional information on the topics covered in this lesson: Students not only want to know how old a fossil is, but they want to know how that age was determined. Some very straightforward principles are used to determine the age of fossils.
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Students should be able to understand the principles and have that as a background so that age determinations by paleontologists and geologists don't seem like black magic. This activity consists of several parts. Objectives of this activity are: A single watch or clock for the entire class will do. Return to top PART 1: After students have decided how to establish the relative age of each rock unit, they should list them under the block, from most recent at the top of the list to oldest at the bottom.
The teacher should tell the students that there are two basic principles used by geologists to determine the sequence of ages of rocks. Younger sedimentary rocks are deposited on top of older sedimentary rocks.
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Principle of cross-cutting relations: Any geologic feature is younger than anything else that it cuts across. For example, U is an unstable isotope of uranium that has 92 protons and neutrons in the nucl eus of each atom. Through a series of changes within the nucleus, it emits several particles, ending up with 82 protons and neutrons.
This is a stable condition, and there are no more changes in the atomic nucleus.
A nucleus with that number of protons is called lead chemical symbol Pb. The protons 82 and neutrons total This particular form isotope of lead is called Pb U is the parent isotope of Pb, which is the daughter isotope. Many rocks contain small amounts of unstable isotopes and the daughter isotopes into which they decay.
Where the amounts of parent and daughter isotopes can be accurately measured, the ratio can be used to determine how old the rock is, as shown in the following activities. That chance of decay is very small, but it is always present and it never changes. In other words, the nuclei do not "wear out" or get "tired". If the nucleus has not yet decayed, there is always that same, slight chance that it will change in the near future.
By correlating fossils from various parts of the world, scientists are able to give relative ages to particular strata. This is called relative dating. Relative dating tells scientists if a rock layer is "older" or "younger" than another. This would also mean that fossils found in the deepest layer of rocks in an area would represent the oldest forms of life in that particular rock formation. In reading earth history, these layers would be "read" from bottom to top or oldest to most recent.
If certain fossils are typically found only in a particular rock unit and are found in many places worldwide, they may be useful as index or guide fossils in determining the age of undated strata. By using this information from rock formations in various parts of the world and correlating the studies, scientists have been able to establish the geologic time scale. This relative time scale divides the vast amount of earth history into various sections based on geological events sea encroachments, mountain-building, and depositional events , and notable biological events appearance, relative abundance, or extinction of certain life forms.
When you complete this activity, you will be able to: The first card in the sequence has "Card 1, Set A" in the lower left-hand corner and represents the bottom of the sequence. If the letters "T" and "C" represent fossils in the oldest rock layer, they are the oldest fossils, or the first fossils formed in the past for this sequence of rock layers. Now, look for a card that has either a "T" or "C" written on it. Since this card has a common letter with the first card, it must go on top of the "TC" card.
The fossils represented by the letters on this card are "younger" than the "T" or "C" fossils on the "TC" card which represents fossils in the oldest rock layer. Sequence the remaining cards by using the same process. When you finish, you should have a vertical stack of cards with the top card representing the youngest fossils of this rock sequence and the "TC" card at the bottom of the stack representing the oldest fossils. Starting with the top card, the letters should be in order from youngest to oldest.
Return to top Procedure Set B: Each card represents a particular rock layer with a collection of fossils that are found in that particular rock stratum. All of the fossils represented would be found in sedimentary rocks of marine origin. Figure 2-A gives some background information on the individual fossils. The letters on the other cards have no significance to the sequencing procedure and should be ignored at this time.
MATERIALS REQUIRED FOR EACH GROUP
Find a rock layer that has at least one of the fossils you found in the oldest rock layer. This rock layer would be younger as indicated by the appearance of new fossils in the rock stratum. Keep in mind that extinction is forever.
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