Earth Science 10: Plate Tectonics

HISTORY - Continental Drift Theory proposed by Alfred Wegener

states that at one point in time, all of the continents were joined together as one large mass of land (PANGAEA - meaning “All of Earth“, a super continent that existed around 300 million years ago), then the land spread apart and drifted into their current positions.

From this, the PLATE TECTONIC THEORY was derived. It is the scientific theory that explains the movements and interactions of Earth’s Tectonic Plates are responsible for many geological features and phenomena.

EARTH - is a DYNAMIC PLANET due to many internal and external factors

2 TYPES OF LAYERS

  1. Compositional - based on materials/elements it is made up of

    • Crust - outermost layer of the earth made of solid rock. There are 2 types of crust:

      • Oceanic Crust

      • Continental Crust

    • Mantle - semiliquid part of the earth where mantle convection occurs

    • Core - the very hot, very dense center of our planet

  2. Mechanical - based on behavior/movement

    • Lithosphere (0-100km) - rigid layer broken into tectonic plates. The 7 major lithospheric plates are:

      • Pacific plate - the largest tectonic plate

      • North American plate

      • Eurasian plate

      • African plate

      • Antarctic plate

      • Indo-Australian plate (Australian Plate)

      • South American plate

    • Aesthonosphere (100-350km) - plastic layer that is directly responsible for the movement of tectonic plates (tectonic plates float on this layer)

    • Mesosphere (350-2900km) - solid layer that forms the lower mantle

    • Outer Core (2900-5100km) - molten (flows) the only true liquid layer of the earth that is responsible for its magnetic field

    • Inner Core (5100-6370km) - solid-ball layer due to intense pressure

PLATE BOUNDARIES - regions where plates interact. There are 3 TYPES OF PLATE BOUNDARIES

  1. Divergent Boundaries (constructive) - occur when two tectonic plates move away from each other 2 TYPES OF DIVERGENT BOUNDARIES:

    • Oceanic-Oceanic Divergent: Sea-floor Spreading (process that adds new materials while pushing away old ones from the ridges). Formation of:

      • Ocean Ridges (Mid-Atlantic Ridge)

      • Volcanic Eruptions at the bottom of the sea

    • Continental-Continental Divergent: Continental Rifting (Magma rises and makes the crust thinner causing it to break over time). These result in:

      • Rift valleys

      • Rift volcanoes

      • New oceans (oceanic crust)

  2. Convergent Boundaries (destructive) - formed when two tectonic plates collide. 3 TYPES OF CONVERGENT BOUNDARIES:

    • Oceanic-Oceanic Convergent: Subduction (The older and denser plate will move beneath the other plate). Leads to the formation of:

      • Volcanoes

      • Volcanic ranges

      • Volcanic island arcs

    • Continental-Continental Convergent: Plates crumpling upwards. Leads to the formation of:

      • High mountain ranges (Himalayas)

      • Shallow-focused earthquakes

    • Oceanic-Continental Convergent: Subduction (Oceanic plate subducts beneath continental plate). Leads to the formation of:

      • Mountain Ranges

  3. Transform Boundaries (conservative) - characterized by plates moving past each other horizontally

    • Faults (San Andreas Fault)

    • Earthquakes

Earthquakes - Vibration of earth’s surface produced by rapid release of energy

  • Hypocenter - point where the earthquake starts

  • Epicenter - point where the earthquake will start at earth’s surface

  • Seismograph - tool used to measure earthquake strength. (Magnitude: 1-10)

TYPES OF EARTHQUAKE WAVES:

  • Body Waves - waves traveling through the earth. 2 TYPES OF BODY WAVES

    • P-waves: (Primary) First waves to hit the seismograph

    • S-Waves: (Secondary) Second waves to hit the seismograph

  • Surface Waves - waves traveling on the surface of the earth

Causes of its Movements

MANTLE CONVECTION - plates float on top of the aesthenosphere, which is a part of the mantle. In the mantle there is a circular motion of pressure where high temperature goes up and lower temperature goes down (convection currents). This makes tectonic plates slowly and gradually move and interact with each other at a rate of 2-10cm per year.