Documents Flashcards Grammar checker. As you take the precarious trail, you notice clear differences in the rock layers. Some layers exhibit a particular color whereas others have unique fossils. What can rock layers reveal to scientists? The study and comparison of exposed rock layers in various parts of the Earth led scientists in the early 19th century to propose that the rock layers could be correlated from place to place. Locally, physical characteristics of rocks can be compared and correlated.
On a larger scale, even between continents, fossil evidence can help in correlating rock layers. The law of superposition, which states that in an undisturbed horizontal sequence of rocks, the oldest rocks will be on the bottom, with successively younger rocks on top of these, helps geologists correlate rocks around the world. This also means that fossils found in the lower levels of a sequence of layered rocks represent the oldest record of life. By correlating fossils from various parts of the world, scientists are able to give relative ages to particular rock layers.
This is called relative dating.
Relative Dating Lab
Relative dating tells scientists if a particular rock layer is older or younger than another. This would also mean that fossils found in the deepest layer of rocks would represent the oldest forms of life. If certain fossils are found only in particular layers of rock, they may be useful as index fossils in determining the age of unknown rock layers.
By using the information from rock formations in various parts of the world and correlating the studies, scientists have been able to construct the geologic time scale. This time scale divides the vast amount of Earth history into sections based on geologic events such as mountain building and biologic events such as extinction.
Spread the cards on the table. Let the cards represent rock layers and the letters represent fossils. Determine the next card by comparing letters that overlap. Sequence the remaining cards by using the same process. Card set A analysis 1. List the cards from oldest to youngest without repeating letters. Examine the second set of cards with sketches of fossils.
Find the list of hypothetical geologic examples and click on "fault. In order to do this, we need to apply the principles of relative dating which we have learned. Complete the sequence correctly and explain the logic and principle behind your choice for each event. Your explanations are as important as the correct sequence in earning the points for this question. Question 2 3 points: Return to the list of hypothetical geologic examples and click on "folds and an intrusion.
Again, complete the sequence correctly and explain the logic and principle behind your choice for each event. Question 3 3 points: Finally, return to the list of hypothetical geologic examples and click on "two intrusions. This is a much more difficult exercise than the previous two because we will find several possibilities for the sequence of geologic events.
You do not need to complete the second half of this particular exercise about resolving these ambiguities in the relative dating. Now let's practice on a couple more imagined cross-sections: Question 4 3 points: What is the sequence of events that can be inferred from the above cross-section?
What principle s of relative dating did you use in order to arrive at your interpretation of the relative timing of each event? The various sedimentary layers are labeled as B, E, K and W. The timing of the fault break in the rocks labeled as Q must be included in the sequence of events.
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Question 5 3 points: The two intrusions are labeled as X and Z; the surrounding rock called the "country rock" is labeled as D. We have seen that a cliff or a road cut is a local "geologic cross-section" -- a side view of the geology at one location.
As geologists piece together the information at various outcrops, they can begin to assemble a "geologic map" like a road map of an entire region consisting of many square miles. This map displays the large-scale also called "regional" geologic features they have inferred are present beneath the landscape. Along with these geologic maps, we can reconstruct a regional geologic cross-section which would be like a great "geologic slice" through the landscape.
In the next lab, we will learn how to use local geologic information from outcrops to begin to build such regional geologic maps and geologic cross-sections, but for now we just want to practice how to read them. Remember when we drew a topographic profile for lab manual exercise 1 page 18 on Topographic Maps?
We could draw such a profile across several miles of landscape so we would see a side-view of the land's surface over which we might be hiking. For example, we could use a ruler to draw a straight line a "transect" from the northwest corner to the southeast corner of the topographic map in our lab kit; then we could draw in the topographic profile along this transect by using the contour line information on the map as done on page In the same way, such a transect could also show the inferred profile of the geology underfoot -- the expected rock layers and structures beneath the land from the northwest corner to the southeast corner of the map.
Take a look at the geologic cross-section below.
You can open a larger version of this diagram by clicking on it. Notice that the various sedimentary layers have been labeled with letters. Also an igneous intrusion is present labeled T and a fault is present labeled A. Question 6 8 points: All 13 lettered events need to be included in your sequence.
Relative Dating Lab
Let's return to one of the text questions we addressed as part of last week's homework. Question 7 8 points: Using the relative dating method you have now practiced, derive the history of the hypothetical landscape on page also shown below. Include all the events which can be inferred from the drawing. List which relative dating principles apply to the order of each event.
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Shown below is a real transect across the entire Grand Canyon in two parts. This profile is comprised of both the surface topography and the inferred geology underfoot.