Unit 4

Plate tectonics

The core… 

• Inner (being solid)

• Outer (liquid)

• Above the core is Mantle

Mantle is seperated into layers: 

Magma/Asthenosphere/lithosphere/ 

• The mantle is divided chemically (by composition) into layers:

  • Upper mantle: Function: The movement in the asthenosphere drives plate tectonics.

  • Lower mantle: Function: Transfers heat upward and helps maintain convection currents in the mantle.

• But the mechanical (physical) structure of Earth (how materials behave) is divided differently:

  • Lithosphere – rigid outer layer (crust + uppermost mantle)

  • Asthenosphere – soft, partially molten part of the upper mantle

  • Mesosphere – strong, rigid layer below the asthenosphere (includes the lower mantle)

  • Outer core and inner core

Who created the Theory of Plate Tectonics: Aflred Wegener

• Earths lithosphere is divided into plates; in motion

Movements of Boundaries

Divergent

Convergent

Transform

🌋 Divergent Boundary

• Definition: Where two tectonic plates move away from each other.

• What happens:

  • Magma rises from the mantle to fill the gap.

  • New crust forms as the magma cools.

• Common features:

  • Mid-ocean ridges (like the Mid-Atlantic Ridge)

  • Rift valleys (like the East African Rift)

• Earthquakes & volcanoes: Usually mild and shallow earthquakes; volcanic activity common.

Faults: Fractures in the rock caused by transform boundary

Island arches: Chain of volances and islands

Collision zone: boths contential to contential zone in pushing

⛰ Convergent Boundary

• Definition: Where two tectonic plates move toward each other.

• What happens depends on the plates involved:

  1. Oceanic–Continental: The denser oceanic plate subducts (sinks) beneath the continental plate.

     • Forms volcanic mountain ranges (e.g., Andes Mountains).

  2. Oceanic–Oceanic: One oceanic plate subducts under the other.

     • Forms volcanic island arcs (e.g., Mariana Islands).

  3. Continental–Continental: Both plates are too light to subduct.

     • Forms large mountain ranges (e.g., Himalayas).

• Earthquakes & volcanoes: Strong earthquakes and volcanic eruptions common (except when both are continental).

⚡ Transform Boundary

• Definition: Where two plates slide past each other horizontally.

• What happens:

  • Crust is neither created nor destroyed.

  • The plates’ rough edges lock, then suddenly release, causing earthquakes.

• Common feature: Fault lines (like the San Andreas Fault in California).

• Earthquakes & volcanoes: Strong earthquakes, but no volcanoes.

Soil formation, erosion, composition, and its properties

Types of rocks formed:

Igneous rock:

• Formed from: Cooling and solidification of magma or lava.

• Types:

  • Intrusive (formed underground; large crystals, e.g., granite)

  • Extrusive (formed on surface; small crystals, e.g., basalt)

sedimentary rock

• Formed from: Compacted and cemented sediments (like sand, mud, or organic material).

• Often formed in: Water environments such as rivers, lakes, or oceans.

• Can contain fossils.

Meta(morphis) rock:

• Formed from: Existing rocks changed by heat and pressure (but not melted).

• Occurs deep underground where temperature and pressure are high.

relating to rock cycle… (slowest of all cycles)

• Tectonics

• weathering (breaking down)

• erosion (movement of weathered rock)

weathering (breaking down): Chemical and physical

Soil formation

• Main factors:

  1. Parent material – the rock that breaks down to form mineral particles.

  2. Climate – temperature and precipitation affect weathering and decomposition.

  3. Organisms – plants, bacteria, and decomposers add organic matter.

  4. Topography – slope and drainage affect erosion and accumulation.

  5. Time – soil formation is very slow (can take hundreds to thousands of years).

Summary Table