Section 11: The Dynamic Planet

SLOs: geologic time scale and Earth's layers, rock types, plate tectonics and plate boundaries.


Lesson 1:

Instruction

The geologic time scale is a timeline summary of history on Earth.  This scale includes relative and absolute time; relative time is defined as the order of events, while absolute time is defined as the actual number of years before present day.  Geology is the study of rocks, tectonics, and hydrology combined.  Therefore, the timeline summary of Earth is based on sampling and analysis of these features on our planet.  Most of the features studied to gain insight about the history of Earth are located within the lithosphere, or Earth's crust.  In general, there are four main layers of Earth from the core (the center of the planet) to the lithosphere (the crust of the planet).  The layers are as follows: the inner core (solid iron and very hot), the outer core (fluid metallic iron with magnetic field generation capabilities), the lower mantle (mostly olivine, iron, magnesium, and silicates with high density), and the upper mantle (mostly less dense olivine and silicates minerals, and including the asthenosphere and the lithosphere).  Now, the asthenosphere is made up of a plastic layer where tectonic events generate because of convective currents.  The lithosphere, however, includes two types of crust: the continental crust (less dense and mainly granite) and the oceanic crust (more dense and mainly basalt).  Because the Earth's crust has different densities and rests upon the asthenosphere, the crust is always in a state of fluxuation termed isostacy.  This fluxuation or adjustment is the reason for all the movements within the crust of our planet.             

Photos and Images
 (Geologic Time Scale)     (layers of Earth)

Quiz

Name the era, period, and epoch we are currently in.  Atop which layer of Earth (-sphere) are you standing right now?  

 


Lesson 2:

Instruction

The sources that fuel the geologic cycle are endogenic and exogenic processes.  Earth's internal heat energy is considered endogenic, while energy from the sun is suggested exogenic.  These processes are what tie together the rock, tectonic, and hydrologic cycles.  Rocks are simply minerals that are assembled and bound together.  Minerals are a combination of elements that are inorganic and crystalline in structure.  Elements that make up minerals that form rocks include: oxygen, silicon, aluminum, iron, calcium, sodium, potassium, magnesium, and other trace elements.  The three main rock types are categorized as igneous, sedimentary, and metamorphic.  Igneous rocks are created from magma (lava in its molten state) that solidifies upon cooling.  Sedimentary rocks are created from other rock types that have been broken up into sediments through weathering, erosion, transportation, and deposition, and then re-compacted through lithification.  Metamorphic rocks are changed from other rock types through heat and pressure, resulting in chemical and physical changes termed metamorphism.  Interestingly enough, all types of rocks can be "recycled" back into the Earth when submerged into a portion of the upper mantle and melted back into magma.              

Photos and Images

 
 (igneous rock) (sedimentary rock)

Quiz

The images above show two of the three rock types.  These have been found and photographed within Ventura County.  Link the rock types above with the characteristics of their formations: extreme heat and pressure, solidification from magma, and compaction over time. 

 


Lesson 3:

Instruction

Hundreds of millions of years ago, the continents on Earth were located much differently than today.  During a period of this time, all the continents were merged into one large land mass called Pangaea.  In more recent periods of time, as the plates of Earth's crust changed position, the Earth's crust formed into what we now experience with 14 major plates.  These plates have been able to move throughout time (continental drift) by multiple plate tectonic processes.  These processes are listed and explained below.  Sea floor spreading and the subduction of Earth's crust are the two most influential methods of plate creation and destruction.  Sea floor spreading occurs at mid-ocean ridges, or large openings in the deep sea floor beds, in which magma upwells and forms new crust.  Subduction occurs at subduction zones either in ocean waters or on high elevations of continents where uplifting is present.  Volcanic eruptions, earthquakes at plate boundaries, and crustal folding are examples of other changes in Earth's crust explained by plate tectonics.  The reason for these changes in planetary crust is because of the influences of the asthenosphere on the lithosphere.  The currents under the crust are moving the plates atop the crust, which are bumping into one another.  There are three types of plate boundary conditions: divergent boundaries (sea floor spreading between two plates), convergent boundaries (subduction of oceanic plates under continental plates), and transform boundaries (plates sliding past one another laterally).  The most well known plate boundary near Ventura County is the San Andreas fault, a transform boundary between the Pacific Plate and the North American Plate, which has caused many earthquakes felt within the V.C.            

             

Photos and Images
    (sea floor spreading plate boundary)          (subduction plate boundary)  (transform plate boundary)    

Quiz

Using the Christopherson text or another source on plate tectonics, name the 14 major plates on Earth.  Also, find the San Andreas fault using Google Earth or a fault map of California.  In which general direction is the San Andreas fault located in comparison with Ventura County?       


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2006 Jessica Douglas