9.1 System and Stratification of Earth
The Earth system consists of four main spheres that interact with one another:
- Atmosphere: The air zone surrounding the Earth's surface (divided into 5 layers: Troposphere, Stratosphere, Mesosphere, Thermosphere, Exosphere).
- Hydrosphere: The water zone including oceans, lakes, rivers, groundwater, and ice caps.
- Biosphere: The life zone inhabited by all living organisms (plants, animals, microorganisms).
- Geosphere: The rock and soil zone forming the solid part of the Earth.
Ocean Stratification
The ocean is divided into three main zones based on light penetration:
- Surface Zone: Shallow depth; sunlight penetrates fully; home to most marine life and photosynthetic plants.
- Midnight Zone: Limited sunlight; deep water; inhabitants are mostly dark-adapted predators.
- Dark Zone: Extremely deep; no sunlight; high pressure and low temperature; organisms rely on bioluminescence or chemosynthesis.
Internal Structure of the Earth
- Crust: Outermost solid layer divided into Continental Crust (granite) and Oceanic Crust (basalt).
- Mantle: Layer below the crust consisting of semi-fluid magma (lithosphere, asthenosphere, mesosphere).
- Core: Innermost layer rich in iron and nickel, divided into a liquid Outer Core and solid Inner Core.
9.2 Composition of the Earth
The Earth's crust is made up of three primary types of rocks:
- Igneous Rock: Formed from the cooling and solidification of magma or lava (e.g., Granite, Basalt). Contains no fossils.
- Sediments & Sedimentary Rock: Formed by the deposition, compaction, and cementation of rock fragments, organic matter, and minerals (e.g., Sandstone, Limestone). Contains abundant fossils.
- Metamorphic Rock: Formed when existing igneous or sedimentary rocks undergo extreme heat and pressure without melting completely (e.g., Marble, Slate). Harder than parent rocks.
9.3 Main Processes of the Earth
Earth processes shape the landscape and are driven by internal and external energy sources:
- Exogenic Processes (External): Occur on Earth's surface (e.g., Weathering, Erosion, Mass Wasting, Transport, Deposition). Driven by solar energy and gravity.
- Endogenic Processes (Internal): Occur inside Earth's crust (e.g., Mantle Convection Currents, Magma Activity, Crustal Movement/Plate Tectonics). Driven by internal heat energy.
9.4 Geohazard Phenomena
- Endogenic Geohazards: Volcanic eruptions, earthquakes, and tsunamis caused by tectonic plate movements.
- Exogenic Geohazards: Landslides, sinkholes, and flash floods caused by weathering, heavy rainfall, or soil instability.
- Quicksand: Formed when water saturates loose sand, reducing friction between particles.
9.5 Age of the Earth
- Geological Time Scale: Divided into Eras (Precambrian, Paleozoic, Mesozoic, Cenozoic).
- Fossils: Remains or traces of ancient organisms preserved in sedimentary rocks. Used by paleontologists to determine relative rock ages and study evolutionary history.
9.6 Earth Resources and Applied Geology
- Surface & Underground Water: Rivers/lakes vs. aquifers and subterranean springs. High risk of pollution from industrial discharge and agricultural leaching.
- Economic Minerals: Metallic minerals (Gold, Iron, Tin) and Non-metallic minerals (Coal, Petroleum, Limestone).
- Hydrothermal Vents: Undersea geysers rich in dissolved minerals that support unique ecosystems without solar energy.