| 1. |
The solid earth is made of |
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Rock |
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Minerals |
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Both above |
| 2. |
Minerals are naturally occurring crystalline compounds that can be defined by a specific chemical composition. In practice, the most common minerals are identified by looking at specific physical properties unique to each: the luster (the way the mineral reflects light), the hardness, the presence or absence of cleavage (the tendency to break into flat planes), and many others. |
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True |
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False |
| 3. |
Rocks are solid aggregates or mixtures of one or more minerals. In other words, a mineral is a single compound, and analysis of any part will give the same composition. A rock consists of _________________ in a solid mass, and thus will provide different compositions as each different part is tested. Rocks are identified as igneous, sedimentary, or metamorphic, based on their origin. |
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Numerous mineral grains |
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Hardly any mineral grains |
| 4. |
One consequence of the rock cycle model is the recognition that truly ancient rocks are very rare. Once exposed the rocks are eroded and become incorporated into younger rocks. As a result, no rocks on the 4.6 billion year old Earth are older than 4 billion years, and in the western United States, the very oldest rocks date back to only 2.7 billion years. The oldest rocks on the Colorado Plateau are but 1.8 billion years old, ____________ the age of the Earth. |
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Twice the age of |
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Less than half |
| 5. |
Geologists and geophysicists see the outer layers of the Earth differently. The crust and uppermost mantle are indeed seen as layers of solid rock, which they collectively call the lithosphere. But beneath the solid lithosphere at a depth of 100 and 200 km (~ 62 and 124 miles) is a layer that is hot nearly to the point of melting, but not quite. This layer, called the asthenosphere, is yielding and capable of flow (Figure 3). |
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True |
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False |
| 6. |
The lithosphere is broken up into a series of what are called plates (somewhat like the pieces of shell on a broken boiled egg). A half dozen or so of the plates are thousands of miles or kilometers across, while others are considerably smaller (Figure 4). The lithospheric plates slide laterally across the asthenosphere, and it this motion that causes apparent continental drift, but the continents are best understood to be passively riding piggyback on the lithosphere. It is at the boundaries between these plates that many of the most important tectonic (Latin: "to build") processes occur, including mountain-building, volcanism, and earthquake activity. In a few short decades, plate tectonics has become the prevailing theory in understanding the workings of planet Earth. |
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True |
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False |
| 7. |
At boundaries, plates may either diverge (separate), converge (come together), or slide past each other (transform boundary). The plate edges may consist of oceanic crust, continental crust, or both (Figure 5). |
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True |
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False |
| 8. |
At divergent boundaries, extensional forces cause the plate edges to ___________, fracturing the crust. The release of pressure in the underlying asthenosphere allows partial melting to take place, and basaltic magma will rise into the fractures as intrusive dikes. The basalt dikes may erupt on the seafloor, forming new oceanic crust. Divergent boundaries can be seen on maps of the ocean floor as oceanic ridges and rift valleys. |
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To move apart |
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To come together |
| 9. |
When divergent boundaries occur on continents, the uplift and spreading will result in rift valleys (the Rio Grande Valley in Colorado and New Mexico is an example) and sometimes basin and range topography, such as is found in Nevada and western Utah. Eventually a new ocean basin will form in between the newly separated continents. This is happening today in the Gulf of California, as Baja California separates from mainland Mexico, moving northwest along the San Andreas fault. Basalt flows on continents may form lava plateaus, like the Columbia Plateau in Washington and Oregon, or the Deccan Traps in India. |
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True |
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False |
| 10. |
A tectonostratigraphic terrane (or simply a terrane) is a fault-bound section of crust that has been moved from its point of origin by divergence or transform fault motions. The islands of New Zealand and the Baja Peninsula are present-day examples. Terranes may also collide with the edge of another continent, forming large mountain ranges, although not on the scale of Himalayan convergence. The mountain ranges of southern Alaska formed in this way. The oldest rocks of the Colorado Plateau formed in large part as a result ________________ . |
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of terrane collisions |
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of earthquake |
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