Model Answer
0 min readIntroduction
The Earth’s outer solid shell, the lithosphere, and the highly viscous, mechanically weak region beneath it, the asthenosphere, are fundamental components of plate tectonics. Understanding their characteristics is crucial for comprehending geological processes like earthquakes, volcanism, and mountain building. Both layers are part of the Earth’s mantle, but differ significantly in their physical and chemical properties, influencing the dynamics of the Earth’s surface.
Lithosphere
The lithosphere comprises the crust and the uppermost solid mantle. It’s approximately 100km thick, varying with oceanic (5-10km) and continental (30-70km) crust. It is brittle and rigid, broken into tectonic plates. Its composition includes silicate rocks rich in aluminum and silicon. Temperature ranges from 0°C to 870°C.
Asthenosphere
Lying beneath the lithosphere, the asthenosphere extends to a depth of about 700km. It is a highly viscous, mechanically weak and ductile region of the upper mantle. While still solid, it exhibits plastic behavior due to high temperatures (870°C to 2200°C) and pressure. Its composition is primarily peridotite, rich in iron and magnesium. The asthenosphere allows the lithospheric plates to move.
| Characteristic | Lithosphere | Asthenosphere |
|---|---|---|
| Depth | 0-100 km | 100-700 km |
| Physical State | Rigid, Brittle | Plastic, Ductile |
| Composition | Silicate rocks (Al, Si rich) | Peridotite (Fe, Mg rich) |
| Temperature | 0-870°C | 870-2200°C |
| Role | Forms tectonic plates | Allows plate movement |
The interaction between these two layers drives plate tectonics, shaping the Earth’s surface over geological timescales. Convection currents within the asthenosphere are believed to be a primary driving force behind plate movement.
Conclusion
In essence, the lithosphere provides the rigid plates, while the asthenosphere acts as a lubricating layer enabling their movement. Their contrasting properties – rigidity versus plasticity, and differing compositions – are fundamental to understanding the dynamic processes occurring within the Earth. The interplay between these layers is critical for the long-term evolution of our planet’s geological features.
Answer Length
This is a comprehensive model answer for learning purposes and may exceed the word limit. In the exam, always adhere to the prescribed word count.