Understand the geomorphological processes that shape Earth’s surface.
Recognize the evolutionary stages of Earth and its layered structure.
Comprehend the geological time scale and major geological eras.
Identify the internal structure of Earth, including the crust, mantle, and core.
Explore the role of seismic waves and other direct and indirect sources in understanding Earth’s interior.
Important Note: Geomorphology is crucial to physical geography, as it explains the origin, development, and mechanisms of Earth’s landforms.
Evolution of Earth and Life
Earth originated around 4.578 billion years ago, initially barren and enveloped by hydrogen and helium. Over time, it evolved into a hospitable planet with water and oxygen-rich atmosphere. The evolution of life, starting around 3800 million years ago, progressed from microscopic algae to fish, amphibians, reptiles, flowering plants, and ultimately, mammals and humans.
Geological Time Scale (GTS)
GTS provides a framework for understanding Earth’s history through stratigraphy. Major geological eras are:
Pre-Palaeozoic Era: Fossil-free rocks; soft-skinned invertebrates in warm seas.
Palaeozoic Era: Development of mountain-building and land-sea intrusion.
Cambrian: Oldest sedimentary rocks; origin of flora and fauna.
Ordovician: Emergence of invertebrates.
Devonian: Known as the Fish Age; amphibians and ferns appear.
Carboniferous: Early reptiles, amphibians, insects, and large trees.
Permian: Formation of potash reserves; varied plant and animal life.
Mesozoic Era: Notable for large reptiles and the breakup of Pangaea.
Triassic: Age of reptiles; emergence of mammals.
Jurassic: Formation of mountains; dinosaurs flourish.
Cretaceous: Angiosperm plants and extinction of dinosaurs.
Cenozoic Era: Formation of major mountain ranges.
Paleocene to Pliocene: Development of mammals, apes, and modern elephants.
Neozoic: Human evolution and end of glaciation.
Blockquote: Geological eras depict evolutionary transitions in both Earth’s structure and life forms.
Earth’s Interior
The Earth, with a radius of 6370 km, has a layered structure inferred from volcanic eruptions, seismic studies, and deep drilling.
Direct Sources
Mining: Solid Earth materials, revealing different compositions with increasing temperature and depth.
Ocean Drilling Projects: Provided insights into crustal structure.
Volcanic Studies: Erupted magma indicates liquid or semi-liquid layers below the crust.
Seismic Studies
Seismology: Study of earthquake waves—P-waves, S-waves, and L-waves—revealing Earth’s internal structure.
P-Waves: Travel through solids, liquids, and gases, providing information about the core.
S-Waves: Traverse only through solids, indicating a semi-liquid mantle.
Important Note: Seismic discontinuities like the Mohorovicic discontinuity (Moho) mark boundaries between Earth’s layers.
Indirect Sources
Temperature and Pressure: Increases with depth, affecting material density.
Meteor Study: Provides insights into Earth’s formation and composition.
Gravity Anomaly: Variations in Earth’s gravity values hint at mass distribution.
Density and Pressure
Density: Surface layer density (2.7 g/cm³) increases with depth to over 11 g/cm³ at the core.
Pressure: Reaches up to 3.5 million atmospheric pressure at the core, influencing its physical state.
Chemical Composition of Earth
The Earth consists of three broad concentric zones:
Crust
Thickness: Varies from 5 km (oceanic) to 70 km (continental).
Composition: Upper continental crust (sial – silica and aluminum) and oceanic crust (sima – silica and magnesium).
Density: Average is 2.7 g/cm³; granite prevalent in continental crust.
Mantle
Thickness: Extends up to 2900 km with an average density of 3.4 g/cm³.
Composition: Rich in olivine; includes the asthenosphere, the source of magma.
State: Solid in lower mantle, semi-liquid in asthenosphere.
Core
Structure: Divided into a liquid outer core and solid inner core.
Density: Ranges from 11 g/cm³ (outer) to 14 g/cm³ (inner).
Composition: Predominantly nickel and iron (nife), controlling Earth’s magnetic field.
Layer
Composition
Density (g/cm³)
State
Crust
Sial, Sima
2.7 – 2.95
Solid
Mantle
Olivine, Magnesium
3.4
Semi-liquid/solid
Outer Core
Nickel, Iron
11
Liquid
Inner Core
Nickel, Iron
14
Solid
Important Note: Discontinuities like Conrad (between upper and lower crust) and Gutenberg (between mantle and core) indicate structural differences.
Types of Rocks
Igneous Rocks: Formed from cooled magma.
Plutonic (deep-seated) and Volcanic (surface).
Classified into felsic (granite) and mafic (basalt).
Sedimentary Rocks: Result from erosion and deposition.
Mechanically formed (sandstone), organically formed (limestone), chemically formed (chalk).
Metamorphic Rocks: Altered by heat, pressure, or chemical processes.