WORLD A · PLANETARY FOUNDATIONS · NODE 03 OF 106
Evolution of Earth
Layered Structure · Lithosphere · Atmosphere & Hydrosphere (28 Micro-Realms)
The Planetary Transformation
From a volatile, barren proto-planet to internal density differentiation (Core, Mantle, Crust), volcanic degassing, primordial ocean condensation (4.0 Ga), and biological oxygenation (2.0 Ga).
VOLATILE EARTH →
DIFFERENTIATION →
LITHOSPHERE →
SOLAR STRIPPING →
DEGASSING →
OCEANS (4.0 Ga) →
OXYGENATION (2.0 Ga)
I. Primordial State & Thermal Differentiation
Barren Proto-Earth
- Volatile rocky state
- Thin H-He gas
- Extreme surface heat
Accretionary Impact Heat
- Planetesimal bombardment
- Kinetic to thermal
- Melts outer shell
Gravitational Compression
- Self-gravity squeezing
- Overlying mass pressure
- Core temperature surge
Radiogenic Heating
- U, Th, K decay
- Spontaneous nuclear heat
- Deep thermal engine
Global Magma Ocean
- Complete interior melting
- Fluid sorting medium
- Hadean molten state
Density Differentiation
- Separation by density
- Heavy sinks inward
- Light floats upward
The Iron Catastrophe
Fe
- Iron & Nickel sink
- Forms metallic core
- Triggers geodynamo
II. Evolution of Lithosphere & Layered Structure
Silicate Upwelling
- Lighter minerals rise
- Silica & Aluminum
- Forms outer crust
Moon-Impact Reheating
- Giant impactor strike
- Secondary melting event
- Ejects lunar debris
Cooling & Contraction
- Heat radiates out
- Crustal solidification
- Surface volume shrinks
Concentric Shell Structure
- Crust, Mantle, Core
- Increasing depth density
- Onion-layer planet
Inner vs Outer Core
- Solid Fe-Ni center
- Liquid outer core
- Magnetic field generator
Mantle & Asthenosphere
- Silicate mantle bulk
- Ductile asthenosphere
- Convective heat cells
Brittle Lithosphere
- Crust plus upper mantle
- SIAL vs SIMA
- Fractured tectonic plates
III. Evolution of the Atmosphere (3 Stages)
Three-Stage Evolution
I→II→III
- Primordial loss stage
- Volcanic degassing stage
- Biological oxygen stage
Stage I: Primordial Loss
- Hydrogen & Helium
- Stripped by solar wind
- Low gravity escape
Stage II: Volcanic Degassing
- Interior expels gases
- Continuous volcanic vents
- Builds secondary air
Early Reducing Air
H₂OCO₂O₂
- Water vapour & N₂
- CO₂, CH₄, NH₃
- Zero free Oxygen
Cometary Volatiles
- Icy impactors strike
- Adds extraterrestrial water
- Enriches gas inventory
Greenhouse Blanketing
CO₂ · CH₄
- High CO₂ & CH₄
- Traps outgoing heat
- Prevents global freeze
Stage III: Bio-Modification
- Cyanobacteria photosynthesis
- Consumes CO₂ gas
- Releases free O₂
IV. Evolution of Hydrosphere & Oxygenation
Atmospheric Cooling
- Surface heat drops
- Steam rises aloft
- Reaches dew point
Global Cloud Canopy
- Thick water clouds
- Envelops entire planet
- Blocks solar rays
The Great Deluge
- Torrential centuries rain
- Liquid reaches surface
- Washes bare rock
Primordial Oceans (4.0 Ga)
- Fills crustal basins
- Forms within 500 Myr
- Ancient marine world
CO₂ Carbonate Sink
CO₂ ↓
CaCO₃
- Rain dissolves CO₂
- Forms carbonate rocks
- Cools planet further
Banded Iron Saturation
- Marine O₂ binds iron
- Rust settles on seabed
- Oceans saturate (~2.5 Ga)
Great Oxidation (2.0 Ga)
- O₂ escapes oceans
- Floods atmosphere (2.0 Ga)
- Forms Ozone shield
Core Distinctions
Differentiation vs. Degassing
Differentiation: Density sorting of solid/molten interior into Core, Mantle, and Crust. Degassing: Outpouring of interior gases/steam to build the atmosphere.
Three Atmospheric StagesStage I: Loss of H/He by solar wind. Stage II: Volcanic degassing (H₂O, CO₂, N₂). Stage III: Biological photosynthesis (O₂).
NCERT Chronology4.6 Ga: Earth · 4.0 Ga: Oceans · 3.8 Ga: Life · 2.5–3.0 Ga: Photosynthesis · 2.0 Ga: Atmospheric O₂.
Density Stratification
Lightest Outer to Densest Center
ATMOSPHERE (N₂ · O₂)
↓
HYDROSPHERE (Oceans)
↓
CRUST (Silicate SIAL/SIMA)
↓
MANTLE (Ultramafic)
↓
CORE (Fe · Ni)