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Is the lava flow older or younger than the rocks that are... ...immediately above it: ...beneath it: Is the sill older or younger than the rocks that are immediately... ...above it: ...beneath it:

Is the lava flow older or younger than the rocks that are... ...immediately above it: ...beneath it: Is the sill older or younger than the rocks that are immediately... ...above it: ...beneath it:

Applications and Investigations in Earth Science (9th Edition)
Applications and Investigations in Earth Science (9th Edition)
9th Edition
ISBN:9780134746241
Author:Edward J. Tarbuck, Frederick K. Lutgens, Dennis G. Tasa
Publisher:Edward J. Tarbuck, Frederick K. Lutgens, Dennis G. Tasa
Chapter1: The Study Of Minerals
Section: Chapter Questions
Problem 1LR
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WINSTIAKA $ FIGURE 1: Cross-section of the earth's surface showing a sequence of layered rocks. Is the lava flow older or younger than the rocks that are... ...immediately above it: Examine Figure 1, and using the descriptions of the mode of formation of lava flows and sills, answer the following questions. ..beneath it: Is the sill older or younger than the rocks that are immediately... ...above it: ...beneath it: SILL 93 LAVA FLOW
Transcribed Image Text:WINSTIAKA $ FIGURE 1: Cross-section of the earth's surface showing a sequence of layered rocks. Is the lava flow older or younger than the rocks that are... ...immediately above it: Examine Figure 1, and using the descriptions of the mode of formation of lava flows and sills, answer the following questions. ..beneath it: Is the sill older or younger than the rocks that are immediately... ...above it: ...beneath it: SILL 93 LAVA FLOW
Many aspects of rock origins are best understood if a rock is considered in terms of its relationships with its neighbors. Such relationships are best seen 'in the field', where the rock is in its natural setting. As an example of this approach, we will consider several field situations to see what light they shed on the origin of rocks. Procedure Three duplicate sets of samples are placed about the room. Work with one set. Each set has 5 boxes, one for each of the 5 exercises that comprise this laboratory. The exercises may be done in any order. Sample Set #1 Age Relationships of Layered Rocks Geologists quantify the immense time spans involved in earth history by establishing a reference point in time, and then counting backwards from that reference point using convenient time units. Geologists use the modem era as a reference point and reckon time backwards to the time of occurrence of a geologic event, as for example, the formation of a rock. Thus, to say that a sandstone is 100 million years old means that 100 million years ago, that sandstone was in the process of formation, perhaps as a sandy beach along an ancient coastline. This is a familiar approach because it is essentially the same as we take in dealing with everyday life. The major difference is that we use different time units (weeks, days, minutes) to measure the short time scales characterizing our day-to-day affairs Geologists can determine the relative ages of the layers in a sequence of layered rocks from the positions of the layers in the sequence. Generally, a given layer is younger than (i.e. formed more recently) the layer below it and older than (i.e. formed before) the layer above it. This idea is referred to as the Principle of Superposition. Figure 1, on the next page, is a cross section showing a horizontal sequence of interbedded sedimentary and igneous rocks, and illustrates how this principle can be applied to interpreting the relative ages of rocks. Figure 1 illustrates also that sometimes the age of specific rock layers may not adhere to the 'younging upward' tenet expressed in the idea of superposition. These exceptions are, however, relatively rare. There are two ways in which the igneous layers diagrammed in Figure 1, may have become part of this sequence: Lava Flow: An igneous layer may be a lava flow which was erupted onto the earth's surface from a volcanic vent. The flowing lava covered the sedimentary rock layers beneath it. At a later time, after the lava had cooled and turned to rock, it was buried by a new influx of sediment, thus becoming part of the layered sequence. Sill: Molten rock, working its way upward through the layered sequence, did not reach the surface of the earth. Instead, while still below ground level, it wedged, or intruded, itself laterally between two of the sedimentary layers in the sequence, where it eventually cooled and became a rock. This intrusive body, called a sill, thus became part of the layered sequence. 92 TARI
Transcribed Image Text:Many aspects of rock origins are best understood if a rock is considered in terms of its relationships with its neighbors. Such relationships are best seen 'in the field', where the rock is in its natural setting. As an example of this approach, we will consider several field situations to see what light they shed on the origin of rocks. Procedure Three duplicate sets of samples are placed about the room. Work with one set. Each set has 5 boxes, one for each of the 5 exercises that comprise this laboratory. The exercises may be done in any order. Sample Set #1 Age Relationships of Layered Rocks Geologists quantify the immense time spans involved in earth history by establishing a reference point in time, and then counting backwards from that reference point using convenient time units. Geologists use the modem era as a reference point and reckon time backwards to the time of occurrence of a geologic event, as for example, the formation of a rock. Thus, to say that a sandstone is 100 million years old means that 100 million years ago, that sandstone was in the process of formation, perhaps as a sandy beach along an ancient coastline. This is a familiar approach because it is essentially the same as we take in dealing with everyday life. The major difference is that we use different time units (weeks, days, minutes) to measure the short time scales characterizing our day-to-day affairs Geologists can determine the relative ages of the layers in a sequence of layered rocks from the positions of the layers in the sequence. Generally, a given layer is younger than (i.e. formed more recently) the layer below it and older than (i.e. formed before) the layer above it. This idea is referred to as the Principle of Superposition. Figure 1, on the next page, is a cross section showing a horizontal sequence of interbedded sedimentary and igneous rocks, and illustrates how this principle can be applied to interpreting the relative ages of rocks. Figure 1 illustrates also that sometimes the age of specific rock layers may not adhere to the 'younging upward' tenet expressed in the idea of superposition. These exceptions are, however, relatively rare. There are two ways in which the igneous layers diagrammed in Figure 1, may have become part of this sequence: Lava Flow: An igneous layer may be a lava flow which was erupted onto the earth's surface from a volcanic vent. The flowing lava covered the sedimentary rock layers beneath it. At a later time, after the lava had cooled and turned to rock, it was buried by a new influx of sediment, thus becoming part of the layered sequence. Sill: Molten rock, working its way upward through the layered sequence, did not reach the surface of the earth. Instead, while still below ground level, it wedged, or intruded, itself laterally between two of the sedimentary layers in the sequence, where it eventually cooled and became a rock. This intrusive body, called a sill, thus became part of the layered sequence. 92 TARI
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