Geology 101, Spring 2017, Quiz 2 Question & Answer Sample

The theory of continental drift assumes that the earth is composed of one continent for billions of years. It slowly drifted apart to form the seven continents which could be recognized in the modern times. The drifting of the continents is mainly due to the lighter rocks at the surface which is influenced or moved by the heavier rocks beneath. On the other hand, the plate-tectonics theory assumes that the earth is composed of plates or slabs which are shifting or moving away or towards each other. The movements of the plate depend on the condition and chemistry of the rocks.
The first main evidence of the plate-tectonics theory is the high amounts of volcanoes or volcanic activities at the boundary of the plates. This evidence suggests interaction among the plates. The second evidence is the seafloor magnetism or seafloor spreading. The stripes of magnetic materials in the sea floor suggest that there is a movement among the plates. The third reason is the fossil evidence. Some of the fossil evidences found at a certain place could also be found on distant places suggesting that land masses are connected in the past.
The magnetic anomaly occurs near the mid-ocean ridges. When lava rises from the ridges to the surface, it cools down. During the cool down, soft rocks moves due to magnetization. In most cases, the magnetic rocks move towards the north magnetic field. The anomalies or variations could be due to the difference in the chemistry or magnetic properties of rocks. After a few hundred years, the earth’s magnetic field changes direction causing the movement of rocks to move parallel to the magnetic stripes.
The state of matter in the earth’s mantle is SOLID.