Geography Optional (Foundations of Earth Sciences) by Anurag Pathak

Model Answer

Question #1. Compare and contrast exogenetic and endogenetic forces in landforms development. 10 marks (150 words)

HINTS

It's essential to appreciate the interplay between these forces. While they might seem opposing— with one building up and the other wearing down— they collectively contribute to the Earth's dynamic landscapes. The understanding of these forces is not just academic but has practical implications.

 For example, recognizing areas prone to tectonic activity can guide urban planning, and understanding erosion can lead to better land management practices. The balance between these forces has continuously sculpted our planet and will continue to do so, illustrating the ever-evolving nature of Earth.

Exogenetic and endogenetic forces play crucial roles in shaping the Earth's surface and creating the diverse landscapes we observe. Here's a comparison based on their origins, mechanisms, effects, and other aspects:

Origin:

• Exogenetic: Originates from external forces, primarily driven by the sun. These include factors such as weathering, erosion, and sedimentation.
• Endogenetic: Originates from the Earth's interior. These forces are due to tectonic activities and the Earth's internal heat, including processes like volcanism and mountain building.
• Mechanism:

 Exogenetic: Processes like chemical, physical, and biological weathering break down rocks. Agents such as water, wind, and ice then transport these materials

 Endogenetic: These forces result from plate tectonics, the movement of magma, and the release of internal pressure, often leading to earthquakes, volcanic eruptions, and mountain formation.

• Effects:
• Exogenetic: They generally result in the wearing down or leveling of the Earth's surface. Examples include valleys, plains, and deltas.
• Endogenetic: Lead to the building up or deformation of the Earth's crust. Examples include mountains, plateaus, rift valleys, and volcanoes.
• Duration & Intensity:
• Exogenetic: Typically, these processes are slow and continuous. However, events like floods can cause rapid and intense landscape changes.
• Endogenetic: They can be both slow, like the movement of tectonic plates, or sudden and catastrophic, such as earthquakes and volcanic eruptions.
• Impact on Life:
• Exogenetic: While processes like erosion and sedimentation might slowly change habitats, extreme events like landslides can have immediate detrimental effects.
• Endogenetic: Earthquakes and volcanic eruptions can cause immediate loss of life and habitat. However, volcanic soil can be fertile, benefiting agriculture in the long run.
• Interactions:

 Often, exogenetic and endogenetic forces don't operate in isolation. Mountains formed by endogenetic processes can be eroded by exogenetic forces. A volcanic eruption (endogenetic) can lead to ash deposition, which can be eroded (exogenetic)

Question #2. Discuss the role of paleomagnetism in confirming the theory of continental drift. Explain how the alignment of magnetic minerals in rocks provides evidence of past continental positions. 15 marks (250 words)

Hints

Divergent plate boundaries are zones where two tectonic plates move away from each other. They play a pivotal role in the formation of new crust on Earth, primarily through the process of seafloor spreading.

Seafloor Spreading:

• Definition: Seafloor spreading is the process by which new oceanic crust forms as magma rises from the mantle to the seafloor at divergent boundaries, solidifies, and then progressively moves away as more magma rises to create new crust.
• Mechanism: As tectonic plates pull apart at a divergent boundary, the reduced pressure allows the partially molten mantle beneath to rise. As this magma reaches the cooler seafloor, it solidifies and forms new oceanic crust.

Mid-Ocean Ridges:

• Definition: These are underwater mountain ranges formed at divergent plate boundaries. They are the most extensive mountain systems on Earth.
• Relation to Seafloor Spreading: Mid-ocean ridges are the sites where seafloor spreading occurs. As magma rises to the seafloor, it solidifies and pushes the existing crust apart, leading to the formation of these ridges. The continuous addition of new magma causes the ridge to grow in elevation.

Creation of Oceanic Crust:

• Composition: The newly formed crust primarily consists of basalt, a dark, dense rock originating from the partial melting of the mantle.
• Lifecycle: As the new oceanic crust moves away from the midocean ridge due to seafloor spreading, it cools, contracts, and becomes denser. Over millions of years, this crust may eventually descend into a subduction zone at a convergent boundary, where it gets recycled into the mantle.

Divergent plate boundaries are essentially Earth's way of rejuvenating and reshaping its surface. While they facilitate the creation of new crust, they indirectly drive the recycling of old crust at convergent boundaries. This dynamic system emphasizes Earth's cyclical nature, where creation and destruction are interconnected.

Additionally, understanding the mechanics of divergent boundaries and seafloor spreading provides insights into various phenomena. For instance, the age of rocks on the ocean floor increases with distance from the midocean ridge, offering a 'tape-recording' of Earth's magnetic field reversals over time.

Furthermore, these processes have implications beyond geology. The hydrothermal vents often found at mid-ocean ridges harbor unique ecosystems, showcasing life's adaptability. And from a resource perspective, these regions are of interest for mining valuable minerals.