1. B

2. C

3. D

4. C

5. C

6. E

7. C

8. A

9. C

10. C

11. C

12. cation-exchange capacity represents the number of "sites" (spots) to which cations can attach on the surface of minerals. It is much higher for some clay minerals than others. This number tells us how many nutrient cations might be available to provide nutrition to plant when the adsorbed cations are taken up by plant roots.

13. This will not be on quiz- we will get to this Monday or Wed.

14. The “Green Revolution” began in the early to mid-1900s, and has greatly increased agricultural production in the face of rising population (and even diminishing cropland) by: mechanization, pesticides, herbicides, irrigation, new crop strains (breeding and now genetic engineering), fertilizers. In the 1950s, the green revolution was applied to the farming in the tropics. The billion dollar question is whether it can be successfully sustained and adopted by poorer and developing countries, many of which are in tropical locations (because of cost of fertilizers and pesticides, soil degradation, continued loss of farmland, loss of water for irrigation, and loss of genetic variability/variety). Even in developed countries, available land for agriculture is declining.

15. The “missing sink” problem (maybe better called the “unidentified sink(s)” problem)=> about 6 GtC are going into atmosphere from fossil fuels per year + another 1-1.5 GtC from land-use change (largely Amazon deforestation) =7-7.5 GtC total; HOWEVER, we can only account for sinks for this excess carbon of about 3.3 GtC in the atmosphere (about 50-60% of the fossil-fuel carbon release) +2.2 GtC in oceans by inorganic dissolution=5.5GtC. So where is the rest of

the carbon (1.5-2 GtC) going, ie, what is the "missing sink"? There must be natural "sinks" for CO2 that have taken it up (for example biological uptake in oceans, reforestation at temperate latitudes, regrowth of deforested tropical forests, uptake by mature tropical forests as found by Phillips); a large amount of research money and effort is going to identifying and understanding those sinks.

16. Erosion would be low in the naturally forested landscape before 1900. The conversion to farm would increase erosion, as agricultural processes commonly leave bare plowed fields for some part of the year, which invites high rates of erosion. With abandonment, natural vegation would begin to re-invade the farm and the land would be covered all year round, thereby reducing erosion. As the land was converted to city, erosion rates would likely be very high when the land was first cleared for construction, but after the construction phase was over, the erosion late would be very low as much of the original soil area becomes covered by buildings and roads.