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UPSC MainsGEOLOGY-PAPER-II201210 Marks
Q28.

Write short notes on :

How to Approach

This question requires concise yet comprehensive notes on a geological topic. The approach should involve identifying key aspects of the topic, structuring the answer logically (definition, processes, significance, examples), and using precise geological terminology. Focus on providing factual information and avoiding overly broad generalizations. The answer should demonstrate an understanding of the underlying geological principles.

Model Answer

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Introduction

Geological time scale is a system of chronological dating that relates geological strata (layers) to time. It is used to describe the timing and relationships between events that have occurred throughout Earth’s history. Developed over centuries through the integration of relative and absolute dating methods, the geological time scale provides a framework for understanding the evolution of life, tectonic activity, and climate change. The current international standard is maintained by the International Commission on Stratigraphy (ICS). Understanding the geological time scale is fundamental to interpreting Earth’s history and predicting future geological events.

Understanding the Geological Time Scale

The geological time scale is divided into hierarchical units: Eons, Eras, Periods, Epochs, and Ages. These divisions are based on significant geological and paleontological events, such as mass extinctions, major changes in climate, and the appearance of new life forms.

Major Divisions of the Geological Time Scale

  • Hadean Eon (4.54 – 4.0 billion years ago): The Earth’s earliest period, characterized by intense volcanic activity and the formation of the Earth’s crust. Very little geological record exists from this time.
  • Archean Eon (4.0 – 2.5 billion years ago): The emergence of the first life forms (prokaryotes) and the formation of early continents. Banded iron formations are characteristic of this eon.
  • Proterozoic Eon (2.5 billion – 541 million years ago): The evolution of eukaryotes, the Great Oxidation Event (increase in atmospheric oxygen), and the formation of supercontinents like Rodinia.
  • Phanerozoic Eon (541 million years ago – Present): The “visible life” eon, characterized by the rapid diversification of life. This eon is further divided into three Eras: Paleozoic, Mesozoic, and Cenozoic.

The Phanerozoic Eon in Detail

Paleozoic Era (541 – 251.902 million years ago)

Marked by the Cambrian explosion (rapid diversification of life), the colonization of land by plants and animals, and the Permian-Triassic extinction event (the largest mass extinction in Earth’s history).

  • Periods: Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian

Mesozoic Era (251.902 – 66 million years ago)

The “age of reptiles,” dominated by dinosaurs. The breakup of the supercontinent Pangaea occurred during this era. The Cretaceous-Paleogene extinction event (caused by an asteroid impact) marked the end of the Mesozoic.

  • Periods: Triassic, Jurassic, Cretaceous

Cenozoic Era (66 million years ago – Present)

The “age of mammals,” characterized by the diversification of mammals and the evolution of humans. The formation of the Himalayas and the opening of the Atlantic Ocean occurred during this era.

  • Periods: Paleogene, Neogene, Quaternary

Dating Methods

The geological time scale is constructed using both relative and absolute dating methods:

  • Relative Dating: Determining the age of rocks and fossils based on their position in the geological record (e.g., superposition, cross-cutting relationships).
  • Absolute Dating: Determining the numerical age of rocks and fossils using radiometric dating techniques (e.g., carbon-14 dating, uranium-lead dating).

Significance of the Geological Time Scale

  • Provides a framework for understanding the history of life on Earth.
  • Helps to correlate geological events across different regions.
  • Aids in the exploration for natural resources (e.g., fossil fuels, minerals).
  • Provides insights into past climate change and environmental conditions.

Conclusion

The geological time scale is a cornerstone of geological science, providing a chronological framework for understanding Earth’s history. Its development has been a continuous process, refined by advancements in dating techniques and paleontological discoveries. Continued research and refinement of the time scale are crucial for addressing contemporary challenges related to climate change, resource management, and understanding the evolution of life on our planet.

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

Radiometric Dating
A method of determining the age of an object by measuring the amount of radioactive decay of specific isotopes within it.
Superposition
In undisturbed sedimentary rock layers, the oldest layers are at the bottom and the youngest layers are at the top.

Key Statistics

The Earth is approximately 4.54 ± 0.05 billion years old.

Source: Dalrymple, G.B. (1991). The Age of the Earth.

The Quaternary Period, encompassing the last 2.58 million years, represents only about 0.057% of Earth’s total history.

Source: International Commission on Stratigraphy (as of knowledge cutoff)

Examples

The Chicxulub Impact

The Chicxulub impact crater in the Yucatan Peninsula, Mexico, provides evidence for the asteroid impact that caused the Cretaceous-Paleogene extinction event, marking the boundary between the Mesozoic and Cenozoic eras.

Frequently Asked Questions

▶What is the significance of index fossils?

Index fossils are fossils of organisms that lived for a relatively short period of time and were geographically widespread. They are used to correlate rock layers and determine their relative ages.

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