The Structure of the Earth Briefly Described

From the inside out, the earth consists of three main layers, the core, the mantle and the crust. The core has a solid inner core and a liquid outer core. The mantle can be broken down into the lower mantle, upper mantle, asthenosphere, and lithosphere. The asthenosphere is a relatively soft and plastic layer. The lithosphere is a very rigid zone that consists of the crust and the uppermost mantle.

The earth's structure

Fig 1. Diagram of the Earth's Structure "WSC10Science - Earth Structure." WSC10Science -
Earth Structure. N.p., n.d. Web. 10 Apr. 2015. <https://wsc10science.wikispaces.com/Earth+Structure>.

Plate Tectonics

Plate tectonics is a theory that really revolutionized the science of geology by linking the internal behavior of the earth to its surface features. It is the theory that the uppermost part of the Earth is made up of 12 rigid lithospheric plates that slowly move laterally over the underlying mantle. The movement of these plates is driven by the convective flow of material in the asthenosphere. This convection starts in the liquid outer core and generally stops at the mantle boundary where heat is then transferred by conduction. However, sometimes these convective currents hit the mantle and continue rising to the base of the crust as vertical currents, called plumes. As these upwelling plumes of hot mantle material impact the base of the lithosphere, they cause lateral spreading, cracking, and rifting. The lithospheric plates continue to split apart and move until they reach a zone of downward flow back into the asthenosphere. This is referred to as a subduction zone.

 Tectonic plates and their directions                the 12 tectonic plates

Fig 2. Map of earth's tectonic plates - type of boundary and direction "G115 - Introduction to Oceanography."                                                               Fig 3. The 12 tectonic plates "Tectonic Plates." Tectonic Plates. N.p., n.d. Web.
G115 - Introduction to Oceanography. The Trustees of Indiana University, n.d. Web. 10 Apr. 2015.                                                                                 10 Apr. 2015.  <http://www.moorlandschool.co.uk/earth/tectonic.htm>.     
<http://www.iupui.edu/~g115/mod04/lecture05.html>.                                                                                          


What is a Subduction Zone?
A subduction zone is a type of tectonic plate boundary where two plates collide and due to density differences one is thrust beneath the other. Subduction zones generally occur in continent to oceanic plate collisions where the denser and thicker oceanic plate is subducted beneath the continental plate with which it is colliding. Subduction zones can also occur between two oceanic plates or two continental plates. We are interested in the continent to oceanic collisions because that is where much of the earths great geological action is occurring. Ever heard of the “Ring of Fire”? The “Ring of Fire” is a string of volcanoes and seismic activity around the edges of the Pacific Ocean. The Pacific Ocean sits atop an oceanic tectonic plate called the Pacific Plate and low and behold this plate is subducting beneath almost all of the surrounding continental plates. The worlds largest earthquakes have all been produced within the “Ring of Fire” on the boundaries of these two colliding plates.

subduction zone diagram   
Fig 4. Diagram of subduction zone "Jul 6 2011 - Taupo Earthquake: Questions and Answers."
- Earthquake. N.p., 06 July 2011. Web. 10 Apr. 2015.
<http://info.geonet.org.nz/display/quake/2011/07/06/Jul+6+2011+-+Taupo+Earthquake%3A+Questions+and+Answers>.

Ring of Fire  

Fig 5. Ring of Fire McLean, Susan, and Patricia Lockridge. "Teachers Guide to Stratovolcanoes of the World." Glossary - Guide to Stratovolcanoes.
National Geophysical Data Center, NOAA, n.d. Web. 10 Apr. 2015. <https://www.ngdc.noaa.gov/hazard/stratoguide/glossary.html>.



Video that is super relevant to the understanding of the "Ring of Fire"




Xxboxingboyxx. "Johnny Cash - Ring of Fire." YouTube. YouTube, 24 Feb. 2009.
Web. 19 Apr. 2015. <https://www.youtube.com/watch?v=It7107ELQvY>.



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