1. The earth’s deep ocean basins have an average elevation that is below sea level and that is much lower than the average elevation of the continents. This is because:
a. The deep ocean basins are composed of oceanic crust, which has a different chemical composition than continental crust, the material of the continents. Oceanic crust is light and buoyant, as opposed to continental crust, which is dense and heavy.
b. The deep ocean basins are composed of oceanic crust, which has a different chemical composition than continental crust, the material of the continents. Oceanic crust is dense and heavy, as opposed to continental crust, which is light and buoyant.
c. The oceanic and continental crusts are chemically indistinguishable from one another and hence have similar buoyancy. It is the weight of the seawater that depresses the oceanic crust, causing the lower elevation of the deep ocean basins.
d. The deep ocean basins are composed of oceanic crust, which has a different chemical composition than continental crust, the material of the continents. Despite this chemical difference, the buoyancy of the two types of crust is equivalent and the ocean basins are at a lower elevation because of the weight of the overlying seawater.
e. The elevation difference between the continents and the deep ocean basins is a legacy of the processes of earth formation 4.5 billion years ago. There has been no change in their configuration since that time and plate tectonics has no influence on the position or elevation of ocean basins versus continents.
2-Consider the processes you know to be active at convergent plate boundaries and take an inventory of the different physical characteristics of the mountain belts that form depending on the type of crust involved in the convergence (think about the crustal type for both plates involved). Consult an atlas of the world to find the following mountain belts: 1) Ural mountains (in Siberia); 2) South Sandwich islands (SE of southernmost South America); 3) Pyrenees mountains (in western Europe); 4) Lesser Antilles islands (in the Caribbean); 5) the mountains on the Indonesian island of Sumatra; 6) the mountains of southern Mexico (from Mexico City southward). Once you locate each belt, examine the most detailed physical map in the atlas for each belt and study the topography (both land and sea) in and near each one. Now pair your observations for each mountain belt with your theoretical understanding of the topographic characteristics of each type of convergent plate boundary to determine which of the following statements is true: (Please note that some of these mountain ranges were formed at plate boundaries that became extinct long ago, so consultation of a map of active tectonics will not be of assistance to you in that case).
a. Mountain ranges 1) and 4) were formed by convergence of two plates each consisting of continental crust; ranges 3) and 6) were formed by convergence between an oceanic and a continental plate, and ranges 2) and 3) were created by convergence between two oceanic plates.
b. Ranges 1) and 3) were created by continental/continental convergence, ranges 5) and 6) by continental/oceanic convergence, and ranges 2) and 4) by oceanic/oceanic convergence.
c. Ranges 2) and 6) were created by continental/continental convergence, ranges 3) and 4) by continental/oceanic convergence, and ranges 1) and 5) by oceanic/oceanic convergence.
d. Ranges 3) and 4) were created by continental/continental convergence, ranges 1) and 6) by continental/oceanic convergence, and ranges 2) and 5) by oceanic/oceanic convergence.
e. Ranges 1) and 6) were created by continental/continental convergence, ranges 2) and 5) by continental/oceanic convergence, and ranges 3) and 4) by oceanic/oceanic convergence.