module 1

• Plate Tectonics - a scientific theory that explains the movement of the earth's lithosphere.
• Plate Tectonics Principle 1 - Plates are driven by cooling of earth.
• Plate Tectonics Principle 2 - Gravity provides additional force to move plates.
• Convection Currents - The flow of heat from one place to another through the transfer of energy.
• The outermost layer of the Earth is called the crust.
• The Earth has three layers, namely the crust, mantle, and core.
• Mantle is the thickest part of the Earth's interior.
• Primary Waves (P) travel faster than secondary waves (S).
• There are three kinds of plate tectonic boundaries: divergent, convergent, and transform plate boundaries.
• All plates are moving because of the convection currents in the mantle.
• At convergent boundaries, two plates collide with one another.
• Plates move away from each other at divergent boundaries.
• Transform boundaries occur when plates slide past each other.
• Continental crust


  Thicker but less dense
• Oceanic crust


  Relatively thinner but denser than continental crust
• According to the plate tectonics model, the entire lithosphere of the Earth is broken into numerous segments called plates
• Plates move very slowly but constantly, and this movement is called tectonics
• Types of seismic waves

  • Primary (P-waves)
  • Secondary (S-waves)
  • Long surface waves (L-waves)
• Earthquake epicenters are distributed in clusters around the world
• When two continental plates converge, a collision zone is formed. Unlike the other two types of convergent boundaries, subduction ceases for this particular type of convergence. No trench, no volcano, and definitely no island arc are created during this process. Instead, what is created is a large group of tall mountains called mountain range.
• About 40 to 50 million years ago, two large land masses, India and Eurasia, collided to begin the formation of the most visible product of plate tectonics - the Himalayas. Since subduction is impossible between two colliding continental plates, pressure is released by pushing the crusts upward and forming the Himalayan peaks.
• Collision of continental plates is associated with shallow earthquake activities.
• Formation of rift valleys and oceanic ridges are indications that the crust is spreading or splitting apart. In this case, the plates are forming divergent plate boundaries wherein they tend to move apart. Most divergent boundaries are situated along underwater mountain ranges called oceanic ridges. As the plates separate, new materials from the mantle ooze up to fill the gap. These materials will slowly cool to produce new ocean floor.
• The spreading rate at these ridges may vary from 2 to 20 cm per year. Although a very slow process, divergence of plates ensures a continuous supply of new materials from the mantle. The Mid-Atlantic Ocean ridge is an example of spreading center which cause
• Divergence of Plates


  1. Formation of rift valleys and oceanic ridges

  2. Plates are forming divergent plate boundaries and moving apart

  3. New materials from the mantle ooze up to fill the gap

  4. The new materials slowly cool to produce new ocean floor

  5. The spreading rate at these ridges may vary from 2 to 20 cm per year
• Divergence of plates ensures a continuous supply of new materials from the mantle
• The Mid-Atlantic Ocean ridge is an example of spreading center which causes the divergence of the South American plate and the African plate
• The rift valley increases its length and depth as the spreading continues. At this point, the valley develops into a linear sea, similar to the Red Sea today.
• In Grade 8, you were introduced to different types of fault such as normal, reverse, and strike-slip. You also learned that faults are fractures in the Earth's crust created by different types of forces acting on the lithosphere.
• There is one type of plate boundary that resembles the strike-slip fault. Though much larger, transform fault boundary is similar to strike-slip fault in terms of the relative motion of adjacent slabs of rock.
• If the blocks of wood in Activity 6 were to represent the lithospheric plates, you will notice that there were two sets of divergent plate boundaries (between blocks 1 and 2, and blocks 3 and 4). But since the plates were adjacent to each other, a new type of boundary is manifested and that is the transform fault boundary.
• Most transform faults join two segments of a mid-ocean ridge (represented by the gaps between 1 and 2, and between 3 and 4). Remember that the presence of a ridge is an indication of diverging plates, and as the plates diverge between the two segments of the mid-ocean ridge, the adjacent slabs of crust are grinding past each other (blocks 2 and 3, blocks 1 and 3, and blocks 2 and 4).
• Although most transform faults are located within the ocean basins, there are a few that cut through the continental crust. An example of this is the San Andreas fault. The immediate concerns about transform fault boundaries are earthquake activities triggered by movements along the fault system.
• It was stated at the beginning of this module that majority of tectonic activities like earthquakes, mountain formations, and volcanic activities happen along or near plate boundaries. But there are some cases wherein activities take place in the middle of a plate.
• Continuing plate movement eventually carries the island beyond the hot spot, cutting it off from the magma source, and volcanism ceases. As one island volcano becomes extinct, another develops over the hot spot, and the cycle is repeated. This process of volcano growth and death, over many millions of years, has left a long trail of volcanic islands and seamounts across the Pacific Ocean floor.
• Mid-ocean ridge


  A continuous mass of land with long width and height on the ocean floor
• Plates


  Rigid sections of the lithosphere that move as a unit
• Plate tectonics


  A theory which suggests that Earth's crust is made up of plates that interact in various ways, thus producing earthquakes, mountains, volcanoes, and other geologic features
• Primary (P) wave


  The first type of seismic wave to be recorded in a seismic station
• Rocks


  Consolidated mixture of minerals