Active Continental Margin and Passive Continental Margin - Assignment Example

Download file to see previous pages The landscape is irregular, comprising both hills and valleys; hence, resulting in short rivers.
On the other hand, in passive continental margins, there is limited tectonic activity; the major processes that occur here are weathering and erosion. This results in level, flat landscapes along the beaches, characterized by long rivers and large debris of sediment.

2. What is the primary reason that the oceanic ridge system is elevated relative to other areas of the ocean floor? 
The oceanic ridge, which is a continuous submarine mountain range spanning 80000 kilometers, is elevated relative to the other areas of the ocean floor. The elevation is brought about by convection currents that rise from deep within the earth’s crust through a mantle in a line of weakness, in the form of magma. When it emerges on the earth’s crust, the lava cools down and forms a new surface on the sea bed. Continuous eruption and cooling of lava lead to a build-up of materials, which in turn causes elevation at the point the activities take place. The result is a ridge, which is higher than other sections of the ocean floor.

3. Explain why the discovery of the fossil remains of Mesosaurus in both South America and Africa, but nowhere, supports the continental drift hypothesis. 
Mesosaurus was a reptile that lived in freshwater lakes thousands of years before the existence of dinosaurs. The fact that scientists found its remains, in Eastern South America and Western Africa only, suggests that the two continents could have existed as one landmass millions of years ago. Whereas some schools of thought could have it that the reptiles could have swum across the Atlantic Ocean, this could not happen since Mesosaurus could neither survive in the ocean waters because of their saltiness nor swim across the ocean due to its expansive nature. These, together with the fact that the coastlines of the two continents fit like pieces of a jigsaw puzzle, enforce the theory that the two continents once existed as one expansive landmass.
4. Discuss the two main objections to the continental drift hypothesis. 

One of the main objections to Wegener’s Continental Drift Theory was his inability to explain the mechanism through which the continents drifted apart. He proposed two theories; a centrifugal force generated by the earth’s rotation, and tides created by the sun and the moon (Sant). However, scientists poked many holes into Wegener’s explanations, rendering them inconclusive.

Secondly, Wegener could not present concrete explanations for the unusual distribution of fossils across continents. Other scientists presented their own theories of how the fossil distribution could have taken place; some suggested the presence of networks of land bridges that connected continents; hence, making it possible for species to cross from one continent to another. Scientists also justified the presence of fossils of temperate species in the arctic by suggesting the presence of warm water currents.

5. Why can oceanic lithosphere be subducted while continental lithosphere cannot? 

The oceanic lithosphere is basaltic, while the continental one is granitic. The differences in density of the materials making their surfaces, therefore, make the oceanic lithosphere denser than the continental lithosphere. In the event of a collision, as is the case in continental margins, the oceanic lithosphere will get subducted because its density is higher than that of the continental plate. On the other hand, if two plates having the continental lithosphere at the top collide, then they will crumble, leading to the formation of hills and mountains. ...Download file to see next pages Read More