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UPSC MainsGEOLOGY-PAPER-I202010 Marks150 Words
Q1.

Discuss the different types of meteorites.

How to Approach

This question requires a descriptive answer outlining the different types of meteorites. The approach should be to categorize meteorites based on their composition – stony, iron, and stony-iron. Within each category, further sub-classification based on specific mineralogy and characteristics should be provided. Mentioning examples of famous meteorite falls will add value. The answer should be concise, sticking to the 150-word limit, and focus on providing a clear and organized overview.

Model Answer

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Introduction

Meteorites are extraterrestrial rocks that have survived passage through the Earth’s atmosphere and impacted its surface. They provide valuable insights into the early solar system’s composition and formation processes. These celestial visitors are broadly classified based on their bulk composition, which reflects their origin within asteroids, planets, or even comets. Understanding these classifications is crucial for deciphering the history of our solar system.

Types of Meteorites

Meteorites are categorized into three main types:

1. Stony Meteorites ( ~95% of falls)

  • Chondrites: Contain chondrules – small, round grains formed in the early solar system. They are the most primitive meteorites.
  • Achondrites: Lack chondrules and are formed from differentiated parent bodies (asteroids that melted and formed layers). Examples include HED meteorites (Howardites, Eucrites, Diogenites).

2. Iron Meteorites (~5% of falls)

Composed primarily of iron-nickel alloy. They originate from the cores of differentiated asteroids that were shattered by collisions.

  • Octahedrites: Most common type, exhibiting Widmanstätten patterns (crystal structures) when etched.
  • Hexahedrites: Contain a higher nickel content and less common patterns.

3. Stony-Iron Meteorites (~1% of falls)

A mixture of silicate minerals and iron-nickel metal.

  • Pallasites: Contain olivine crystals embedded in an iron-nickel matrix.
  • Mesosiderites: Breccias (rocks composed of fragments) containing silicate and metal components.
Type Composition Origin
Stony (Chondrite) Silicates, Chondrules Primitive Asteroids
Iron (Octahedrite) Iron-Nickel Alloy Asteroid Cores
Stony-Iron (Pallasite) Silicates & Iron-Nickel Core-Mantle Boundary of Asteroids

Conclusion

In conclusion, meteorites are classified primarily by their composition – stony, iron, and stony-iron – each providing unique clues about the formation and evolution of the solar system. The study of these extraterrestrial rocks continues to refine our understanding of planetary processes and the origins of Earth itself. Further research, including isotopic analysis, helps pinpoint their specific parent bodies and refine our cosmological models.

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.

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Additional Resources

Key Definitions

Chondrule
A small, round grain found in chondrite meteorites, believed to have formed in the early solar system from dust and gas.
Widmanstätten Pattern
A characteristic crystalline pattern found in iron meteorites when etched with acid, revealing the intergrowth of kamacite and taenite (iron-nickel alloys).

Key Statistics

Approximately 500 meteorites reach the Earth's surface each year, but the vast majority are not recovered.

Source: NASA (as of knowledge cutoff 2023)

Around 60% of all recovered meteorites originate from the asteroid belt between Mars and Jupiter.

Source: Meteoritical Society (as of knowledge cutoff 2023)

Examples

Hoba Meteorite

The Hoba meteorite, found in Namibia, is the largest known intact meteorite. It is an iron meteorite weighing approximately 60 tons.

Frequently Asked Questions

▶What is the difference between a meteoroid, a meteor, and a meteorite?

A meteoroid is a small rock or particle in space. A meteor is the streak of light seen when a meteoroid enters the Earth's atmosphere (a "shooting star"). A meteorite is the portion of a meteoroid that survives the atmospheric passage and reaches the ground.

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