) to the air, becoming a strong base B. Gains carbon dioxide (CO 2 ) from the air, becoming a weak acid C. Neither gains nor loses carbon dioxide (CO 2 ) D. Gains humic compounds from the air, becoming a strong base E. None of the above CO 2 is fairly soluble in water, so rain picks some up from the air, and adding CO 2 makes water a little more acidic. Humic compounds are picked up from soil by water, and make the water more acidic. Points Earned: 1/1 Correct Answer: B Your Response: B 5. Chemical weathering of a continental rock such as granite in a climate such as that of Pennsylvania produces: A. Salt-laden soils (also called pedocals) B. Clays that dissolve and wash away easily C. Clays and rust, that do not wash away easily, and soluble ions, that do wash away easily D. Feldspar and dark-mineral grains, that do not wash away easily, and dissolved quartz that does wash away easily E. Soluble ions that do not wash away easily, and clays and rust that wash away easily Weathering of granite in Pennsylvania makes some things (clay, rust, and quartz sand) that stay behind to contribute to soil, and other things (soluble ions) that dissolve and wash away very quickly. In dry climates, not very much rainwater percolates downward and through rocks to streams; most rain soaks in a little bit, but is evaporated back to the atmosphere before soaking way down in soil. Very soluble things (sodium ions, for example) may wash away in the little water that reaches streams, but slightly less soluble things (which would wash away in
Pennsylvania) such as calcium will be released from rocks but then accumulate in spaces in the soil as water evaporates. These give rise to pedocals, calcium-laden soils. But these are not expected in rainy Pennsylvania, and this isn’t a subject introduced in the course, so you really shouldn’t worry about it. Points Earned: 1/1 Correct Answer: C Your Response: C 6. Calcium released by chemical weathering is transported by streams to the ocean, where much of it: A. Is used by clams, corals, etc. to make their shells B. Evaporates from the ocean and rains back out on the land C. Is subducted back into the mantle at the mid-ocean ridges D. Is extracted from the water by marine dairy cows to add to milk E. Builds up in the water, making the ocean saltier Most common shells seen at the beach are calcium carbonate, and the calcium is provided by weathering of rocks on land. Calcium ions do not evaporate easily, and are not very common in the atmosphere. A little bit of sea salt, and anything else small in the sea, does escape in spray (stand by the sea on a windy day and you’ll get spots on your sunglasses), but most of the calcium reaching the sea is used there. The “saltiness” of the ocean is a quite different chemical, not calcium. Some shells are subducted, many more are scraped off downgoing slabs at subduction zones, but subduction does not occur at mid-ocean ridges, which is where sea floor is made, not where sea floor is consumed. Calcium in milk is a good thing, and helps build
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