Question

mid - term study guide
29 why does earth have a magnetic field?
plate tectonics
30 where is continental crust?
31 where is oceanic crust?
32 what are the three types of convergent boundaries, and describe where they are located?
weathering
33 what is physical weathering?
34 list three types of physical weathering and describe them.
35 what is chemical weathering?
36 list three types of chemical weathering and describe them.

Explanation:

1. Earth's magnetic field is due to the motion of molten iron - nickel in its outer core creating electric currents which generate a magnetic field through the dynamo effect.
2. Continental crust is found under the continents, it is thicker and less dense than oceanic crust.
3. Oceanic crust is found under the oceans, it is thinner and denser than continental crust.
4. The three types of convergent boundaries are: ocean - continent (where an oceanic plate subducts under a continental plate, e.g., along the western coast of South America), ocean - ocean (where one oceanic plate subducts under another, e.g., the Mariana Trench), and continent - continent (where two continental plates collide, e.g., the Himalayas).
5. Physical weathering is the breakdown of rocks into smaller pieces without changing their chemical composition, mainly through mechanical forces.
6. Three types of physical weathering: Frost wedging (water freezes in cracks in rocks, expands, and breaks the rock), exfoliation (due to pressure release as overlying rocks are eroded, outer layers of rock peel off), and abrasion (rocks are worn down by friction from other rocks or particles).
7. Chemical weathering is the breakdown of rocks through chemical reactions that change the rock's chemical composition.
8. Three types of chemical weathering: Oxidation (e.g., iron in rocks reacts with oxygen to form rust), carbonation (carbon dioxide in water reacts with calcium carbonate in rocks like limestone), and hydrolysis (water reacts with minerals in rocks to form new minerals).

Answer:

1. Earth's magnetic field is generated by the motion of molten iron - nickel in its outer core creating electric currents via the dynamo effect.
2. Under the continents.
3. Under the oceans.
4. Ocean - continent (e.g., western coast of South America), ocean - ocean (e.g., Mariana Trench), continent - continent (e.g., Himalayas).
5. The breakdown of rocks into smaller pieces without changing their chemical composition by mechanical forces.
6. Frost wedging (water freezes in cracks, expands, breaks rock), exfoliation (pressure - release causes outer layers to peel off), abrasion (worn down by friction).
7. The breakdown of rocks through chemical reactions that change the rock's chemical composition.
8. Oxidation (iron reacts with oxygen to form rust), carbonation (carbon dioxide in water reacts with calcium carbonate), hydrolysis (water reacts with minerals to form new minerals).