Geological Time Scale, Earth Structure and Planetary Spheres
Geological Time Scale and Deep Time
The Geological Time Scale (GTS) is the calendar for Earth’s 4.54-billion-year history. It organizes the vast expanse of deep time into nested units based on major geological events (like mountain building) and biological shifts (like mass extinctions). Scientists use chronostratigraphy (stacking rock layers) and geochronology (radiometric dating) to refine these dates.
Hierarchy of Time Divisions
Geological time is divided into units of varying lengths, from the
Read MoreEcosystem Factors and Biogeochemical Cycling Principles
Ecosystem Components and Influences
The environment is shaped by a complex interplay of abiotic (non-living) and biotic (living) factors, which collectively determine the nature of ecosystems worldwide.
Abiotic Factors (Physico-Chemical)
Abiotic factors are the non-living components of the environment that influence the survival, growth, and distribution of organisms.
Climatic Factors
These are largely controlled by weather patterns and include:
- Light: The primary source of energy. Its characteristics
Sedimentology Concepts: Grain Size, Transport & Diagenesis
Sedimentology Concepts: Grain Size, Transport & Diagenesis
(a) Krumbein’s Logarithmic Transformation (φ scale)
Why is Krumbein’s logarithmic transformation necessary? Grain-size data are not normally distributed but are skewed. Krumbein introduced the phi (φ) scale to convert grain size into a logarithmic form: φ = −log₂ (grain diameter in mm). This transformation simplifies statistical analysis of sediments and helps in easy comparison of grain-size parameters like mean, sorting, skewness,
Read MoreSedimentary Petrology: Transport and Lithification
Recap of Sedimentary Rock Formation
UNIT I (b): Transportation, Deposition & Lithification (Sedimentary Petrology – CC VI)
Background Concepts
Before understanding transportation and deposition, we must recall what happens before sediments move:
Sedimentary Rocks
- Formed by the accumulation, deposition, and lithification of sediments.
- They cover approximately 75% of the Earth’s surface.
Weathering
Weathering is the breakdown of rocks in situ.
- Physical weathering: Mechanical disintegration with no
Igneous Rocks: Formation, Textures, Magmatism and Occurrences
Mode of Occurrence of Igneous Rocks
Igneous rocks are formed by the cooling and solidification of molten magma either beneath the Earth’s surface or on it. Their mode of occurrence is closely related to the depth of crystallization, the nature of magma intrusion, and the environment in which the magma solidifies. Broadly, igneous rocks occur in two main modes: intrusive (plutonic) and extrusive (volcanic).
Intrusive (Plutonic) Igneous Rocks
These rocks form when magma cools slowly beneath the Earth’
Read MoreIndian Sedimentary Basins and Sedimentary Structures
1. Sedimentary Basins
Definition: A sedimentary basin is a low-lying area of the Earth’s crust that undergoes subsidence and accumulates sediments over geological time.
Sediments may be clastic, chemical or biogenic.
Basins preserve information about tectonics, climate, provenance and resources.
2. Physiography of India and Basin Settings
India shows diverse physiographic divisions.
Major units:
- Himalayan orogenic belt
- Indo-Gangetic plain
- Peninsular craton
- Coastal plains
- Continental shelf and deep sea
Basin