The Earth and Its Origin: Interior Structure, Evolution and Geological Time
The Earth and Its Origin: Interior Structure, Evolution and Geological Time
This domain tests origin theories, the layered interior, seismic evidence for those layers, and the geological time scale. Expect matching, sequencing and 'which discontinuity' questions.
Core rules and concepts
- Origin theories: nebular hypothesis (Kant, later Laplace), planetesimal hypothesis (Chamberlin and Moulton), tidal hypothesis (Jeans), and the modern Big Bang/nebular account.
- Interior layers: crust (continental 30–70 km; oceanic 5–10 km), mantle to about 2,900 km, core to 6,371 km. The outer core is liquid; the inner core is solid.
- Discontinuities: Mohorovičić (Moho) between crust and mantle; Repetti between upper and lower mantle; Gutenberg between mantle and core; Lehmann between outer and inner core.
- Seismic waves: P waves pass solids and liquids and are faster; S waves pass only solids and create a shadow zone between 103° and 142° from the focus.
- Geological time: Hadean, Archaean, Proterozoic and Phanerozoic eons; Phanerozoic eras are Palaeozoic, Mesozoic and Cenozoic.
Worked example
S waves are not recorded beyond 103° from an earthquake focus. Reasoning: S waves cannot travel through liquid, so a liquid outer core blocks them; beyond the shadow zone they reappear only as P waves refracted around the core. This is direct evidence that the outer core is fluid, not solid.
Traps
Do not place the Moho between mantle and core. Do not say the whole core is liquid. Do not mix era and period order (Cenozoic is an era, Pleistocene a period).