Name ______Name ______Date ______Class Period _____ Date ______Class Period _____ Instructor ______Lab Period ______Instructor ______Lab Period ______5 points Correlation
Sequence A Sequence B Cut and paste rocklayers Cut and paste rocklayers youngest youngest
oldest oldest Age of Known Fossils m.y.a. (millions of years ago) Questions: For #1-5, write complete sentences. Do not use personal pronouns. 3 points each.
1.
2.
3.
4.
5.
6. A B C D
7. A B C D
8. A B C D
9. A B C D
10. A B C D Lab #32 Correlation INTRODUCTION: Geologist can determine the relative ages of rock layers within one outcrop of rock. Determining relative ages of rock layers from multiple outcrops is much more difficult. This process is called correlation. Comparing similar layers, sequences and thicknesses of rocks can be helpful. Volcanic ash and dust from large meteorites often deposit over widespread areas over a short period of time. These would also make good time markers. Index fossils are also used to determine relative as well as absolute ages. Index fossils are fossils of creatures that existed for a short period of time but lived over a wide geographic area.
PROCEDURE: A: Reconstruct the complete sequence of events for the rock columns A – D. Cut out the symbols for the rock layers and paste them in order on the report sheet. The oldest layer should be put on the bottom. B: Reconstruct the complete sequence of events for the rock columns A – D. In order to complete the correlation, the Earth Science Reference Tables (p.8) should be used to give the relative ages of the index fossils. Cut out the symbols for the rock layers and paste them in order on the report sheet. The oldest layer should be put on the bottom. In the column to the right of Sequence B, write in the range of ages for the known fossils.
QUESTIONS: 1. Why are rock layers representing certain time periods missing from some columns of rocks?
2. What is the approximate age of the bottom of the sequence in Sequence B?
3. Approximately how many years separate the top of Sequence B and the bottom of Sequence B?
4. Why might a fossil be found in a rock layer at one location but not in the same rock layer at another location?
5. Why would scientists use sequences from many locations to obtain a complete sequence of events? 6. In a certain section of sedimentary rock, fossil dating shows that younger rock layers are on top of older layers. This relationship indicates that:
A. the rock layers were formed according to the law of superposition B. the rock layers were overturned C. fossil dating is inaccurate D. the sediments that formed the rock layers were composed of many different minerals
7. The simplest way to correlate exposed rock layers in the same general vicinity when they contain no fossils is by A. following vertical rock veins B. radioactive dating C. walking the outcrop D. tracing a fault
8. The fossil remains of organisms which were once common and widespread but which only survived for a short period of geologic time might be useful for A. correlating sedimentary rocks in places distant from each other B. establishing the absolute age of a deposit C. tracing the evolution of an organism D. determining the cause of the organism’s extinction
9. Why can layers of volcanic ash found between rock layers serve as good geologic time markers? A. Volcanic ash usually occurs in narrow bands around volcanoes B. Volcanic ash usually contains index fossils C. Volcanic ash usually contains radioactive carbon-14 D. Volcanic ash usually is deposited over a large area
10. According to the Earth Science Reference Tables, which rock materials is most likely the oldest? A. conglomerate containing the tusk of a mastadon B. shale containing trilobite fossils C. sandstone containing fossils of flowering plants D. siltstone containing dinosaur footprints A. Outcrops From Four Locations B. Rock Strata (layers) Containing Index Fossils
INDEX FOSSILS - Use the Reference Tables to determine relative ages Cut out symbols for rock layers. Keep the two sequences separated.
Sequence A
Sequence B