Understanding Eutrophication, Plate Tectonics, and Earth's Layers

Eutrophication

Eutrophication is the increase in nutrients, which increases the number of producers. This makes the water cloudy and prevents photosynthesis from taking place in the deeper levels, as there is a lack of sunlight. Heterotrophic organisms and decomposers intensify their activity, as there is more organic matter available. They also increase their oxygen consumption. In the end, the oxygen in the deeper level runs out, making it impossible for most species to survive.

Theory of Continental Drift

1912-1960: 225 million years ago, all the continents were joined together as one large supercontinent called Pangea. Over a very long period, the continents drifted apart to the positions they are today.

Evidence for Continental Drift

• Geological: Continental shelves fit together even better than the coastlines.
• Paleontological: Identical fossils of land organisms are found on continents that are now separated.
• Paleoclimate: It is suspected that the northern part of Pangea was covered in large tropical rainforests, while the Southern Hemisphere was covered in glaciers.

Isostasy

Isostasy is the equilibrium between the lithosphere and the underlying asthenosphere.

Subduction

Subduction is the process in which the oceanic lithosphere moves under the continental lithosphere and into the mantle.

Plate Tectonics

Plate tectonics states that the lithosphere is divided into large pieces called plates. They cover the surface and fit together. Volcanoes and earthquakes are located at the borders between the plates. The ocean floor is continually being formed at ocean ridges and being destroyed at trenches. Plate movements move the continents; where two plates move apart, new oceans are generated.

Wilson Cycle

1. A dome forms: The heat under the continent causes the crust to expand and lift.
2. Continental rift stage: Large fractures appear, which make the lithosphere thinner and lead to the formation of a continental rift.
3. Narrow sea stage: The continent has completely split and separated. New oceanic lithosphere and a small ridge begin to form between the two sides.
4. Maturing ocean stage: The divergence continues, and the formation of oceanic lithosphere due to seafloor spreading increases.
5. Shrinking ocean stage: The ocean begins to close because of subduction on its boundaries.
6. Convergence stage: The ocean has almost closed. The continents converge with marine sediments on their edges.
7. Continental collision stage: The boundaries of both continents and the sediment trapped between them are deformed.
8. Final stage: The continental masses are joined together, and a mountain range is formed from the collision of the continents. Eventually, the plate boundary will become inactive.

Compositional Layers of the Earth

The Earth is composed of several layers, separated by discontinuities:

• Moho: 15-70 km deep
• Repetti: 800 km deep
• Gutenberg: 2900 km deep
• Lehmann: 5100 km deep