Mains Practice Question


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What is the geological time scale (GTS)? Describe the historical evolution of the geological time scale.


A Simple Introduction about Geological time scale

The geological time scale is a framework used by scientists to chronologically divide and categorize Earth's history into distinct intervals based on significant geological, biological, and climatic events. This timeline allows researchers to understand the sequence of events that have shaped the planet over billions of years.

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Evolution of the Geological Time Scale

Origins and Early Breakthroughs

The foundation of the geological time scale traces back to the 1500s and 1600s, with a significant milestone occurring in 1669 when Danish scientist Nicolas Steno published the first laws of stratigraphy. Stratigraphy is the science of interpreting the layers of rock, or strata, on Earth's surface.

Steno's Principles:

Steno established two fundamental principles:

  1. Horizontal Deposition: Sedimentary rocks, formed on or near the Earth's surface, are initially laid down horizontally.

  2. Superposition: Successive rock layers are deposited on top of older layers. This principle implies that layers closer to the Earth's surface are younger than those beneath them.

Arduino's Classification:

Italian geologist Giovanni Arduino further advanced geological understanding by classifying the Earth's crust into four main layers:

  1. The Primary Layer is The lowest layer comprised of metamorphic and volcanic rocks.
  2. The Secondary Layer Consists of hard sedimentary rocks.
  3. The Tertiary Layer Comprising less hardened sedimentary rocks.
  4. The Quaternary Layer is the most recent, relatively soft compared to others, representing the most recently deposited rocks.

Challenges and Limitations

  1. Local Descriptions: Rock formations were often described based on local characteristics such as colour, texture, or odour, hindering comparisons between different regions.

  2. Absence of Absolute Time: Unlike tree-ring dating, which provides a direct annual measure, rock layers do not offer precise time intervals. Each layer represents a period of geological time, but the duration of these periods cannot be determined solely from the layers.

The 1800s brought a breakthrough in geological time-scale development. English surveyor William Smith recognized that fossils held the key.  He realized that distinct fossil types characterized specific periods.  For instance, a rock with a trilobite fossil belonged to the Paleozoic era (541-252 million years ago) because trilobites were exclusive to that period.  This observation laid the foundation for a more precise understanding of Earth's history.
The ending of the answer should be on a positive note and it should have a forward-looking approach.

The geological time scale continues to evolve as discoveries and advancements in dating techniques emerge. Its significance lies in its ability to provide a chronological framework for studying Earth's history and understanding the processes that have shaped our planet over geological time scales.


Other Points to Consider 

Different types of rocks

Soil profile

Difference between categories of GTS


Previous Year Questions

1. Describe the characteristics and types of primary rocks. (2022)


22-May 2024