OUR DYNAMIC EARTH OUR DYNAMIC EARTH

In what way or ways is our In what way or ways is our Earth a dynamic planet?Earth a dynamic planet?

PS5 PS5

UNIT OBJECTIVESUNIT OBJECTIVES

YWBAT: Define that time is an important component of every

geological process, and demonstrate understanding of the scope of the time line of geologic development.

Identify natural processes that help change the Earth.

Identify the internal structure of the planet Earth. Describe constructive and destructive forces that

shape the land.

Structure of the EarthStructure of the Earth• The Earth is an oblate spheroid. It is composed of a

number of different layers as determined by deep drilling and seismic evidence (Figure 10h-1). These layers are:

• The core which is approximately 7000 kilometers in diameter (3500 kilometers in radius) and is located at the Earth's center.

• The mantle which surrounds the core and has a thickness of 2900 kilometers.

• The crust floats on top of the mantle. It is composed of basalt rich oceanic crust and granitic rich continental crust.

• pp. 108 - 117 in the text•

THEORY OF PLATE TECTONICSTHEORY OF PLATE TECTONICS• Theory development (pp 118-129 in text)

– 1600’s – maps began to get into the hands of common people; Francis Bacon (1620) noted the similarity of the shape of the continents on either side of the Southern Atlantic; Francois Placet (1666) suggested that prior to the Great Flood the land was undivided by oceans and that the Atlantic formed when Atlantis sank.

– 1912 – Alfred Wegener presented the Continental Drift Theory which stated that the continents were once joined together (Pangaea); over time they drifted apart.

THEORY OF PLATE TECTONICS THEORY OF PLATE TECTONICS (CONT.)(CONT.)

• In the 1960’s, new evidence caused scientists to reconsider Wegener’s theory - who, what and why?

So, How Does This Happen?So, How Does This Happen?• The Earth releases its internal heat by convecting, or

boiling much like a pot of pudding on the stove. Hot asthenospheric mantle rises to the surface and spreads laterally, transporting oceans and continents as on a slow conveyor belt. The speed of this motion is a few centimeters per year, about as fast as your fingernails grow. The new lithosphere, created at the ocean spreading centers, cools as it ages and eventually becomes dense enough to sink back into the mantle. The subducted crust releases water to form volcanic island chains above, and after a few hundred million years will be heated and recycled back to the spreading centers. Complete WS “ What’s Happening During Convection?”.

Types of Plate Tectonic BoundariesTypes of Plate Tectonic Boundaries

• There are three main plate tectonic environments: transform, convergent, and divergent. Plate boundaries in different localities are subject to different inter-plate stresses, producing these three types of earthquakes. Each type has its own special hazards.

• At transforms (strike-slip faults), earthquakes are shallow, running as deep as 25 km; mechanisms indicate strike-slip motion. Transforms tend to have earthquakes smaller than magnitude 8.5.

• The San Andreas fault in California is a nearby example of a transform, separating the Pacific from the North American plate. At transforms the plates mostly slide past each other laterally.

• At convergent boundaries (reverse faults), earthquakes are found in several settings ranging from the very near surface to several hundred kilometers depth, since the coldness of the subducting plate permits brittle failure down to as much as 700 km. Convergent boundaries host Earth's largest quakes, with some events on subduction zones in Alaska and Chile having exceeded magnitude 9.

• At spreading ridges, or similar divergent boundaries (normal faults), earthquakes are shallow, aligned strictly along the axis of spreading, and show an extensional mechanism. Earthquakes in divergent environments tend to be smaller than magnitude 8.

Earthquake occurrence in Earthquake occurrence in different plate tectonic settings:different plate tectonic settings:

• This map of Earth's solid surface shows many of the features caused by plate tectonics. The oceanic ridges are the asthenospheric spreading centers, creating new oceanic crust. Subduction zones appear as deep oceanic trenches. Most of the continental mountain belts occur where plates are pressing against one another. The white squares locate examples given here of the different tectonic and earthquake environments.

What Is Seismology?What Is Seismology?Seismology is the study of earthquakes and seismic waves that move

through and around the earth. A seismologist is a scientist who studies earthquakes and seismic waves.

What Are Seismic Waves?• Seismic waves are the waves of energy caused by the sudden

breaking of rock within the earth or an explosion. They are the energy that travels through the earth and is recorded on seismographs.

• Types of Seismic Waves• There are several different kinds of seismic waves, and they all

move in different ways. The two main types of waves are body waves and surface waves. Body waves can travel through the earth's inner layers, but surface waves can only move along the surface of the planet like ripples on water. Earthquakes radiate seismic energy as both body and surface waves.

P WAVESP WAVES• The first kind of body wave is the P wave or primary wave. This is the

fastest kind of seismic wave. The P wave can move through solid rock and fluids, like water or the liquid layers of the earth. It pushes and pulls the rock it moves through just like sound waves push and pull the air. Have you ever heard a big clap of thunder and heard the windows rattle at the same time? The windows rattle because the sound waves were pushing and pulling on the window glass much like P waves push and pull on rock. Sometimes animals can hear the P waves of an earthquake. Usually we only feel the bump and rattle of these waves.

The arrow shows the direction that the wave is moving.

S WavesS Waves

The second type of body wave is the S wave or secondary wave, which is the second wave you feel in an earthquake. An S wave is slower than a P wave and can only move through solid rock. This wave moves rock up and down, or side-to-side.

The arrow shows the direction that the wave is moving.

SURFACE WAVESSURFACE WAVES

• Surface waves move the ground up and down in circles and do not affect the rock deep below the surface.

• They travel more slowly and are more destructive. Most Earthquake damage comes from surface waves.

EARTHQUAKE MEASUREMENTEARTHQUAKE MEASUREMENT

• seismographs – instruments that record seismic waves, creates a seismogram

• epicenter – point on Earth’s surface directly above the Earthquake’s origin

• focus – actual point of origin inside the Earth• S-P time – method used to find the epicenter of a quake• Mercalli Scale – rates earthquakes by their intensity; not

an exact measurement• Richter scale – used to measure quake intensities;

named after Charles Richter who developed it in the 1930s

Complete WS AND read pages 154-159 in text.

SUMMARY NOTESSUMMARY NOTES The solid Earth is layered with a lithosphere (crust); hot, CONVECTING mantle; and a

dense, metallic core. The outward transfer of Earth’s internal heat drives CONVECTION in the mantle that

propels the plates comprising Earth’s surface across the face of the globe. Lithospheric plates on the scales of continents and oceans constantly move at rates

of centimeters per year in response to movements in the mantle. Major geological events, such as earthquakes, volcanic eruptions, and mountain building, result from these plate movements.(CONTINENTAL DRIFT, PLATE TECTONICS, SEA FLOOR SPREADING, FAULTS, BOUNDARIES)

Landforms are the result of a combination of constructive and destructive forces. Constructive forces include crustal deformation, volcanic eruption, and deposition of sediment, while destructive forces include weathering and erosion.

The Earth processes that we see today are assumed to be similar to those that occurred in the past (Uniformitarianism)

Earthquakes Getting Ready for Earthquakes Getting Ready for the Big Onethe Big One

INTERNET RESOURCESINTERNET RESOURCEShttp://www.usgs.govhttp://quake.wr.usgs.govhttp://jei.umd.edu/agi/agi.htmlhttp://www.geosociety.orghttp://www.uic.edu/orgs/paleo/

homepage.html

WORKS CITEDWORKS CITED• www.seismo.unr.edu/ftp/pub/louie/ class/100/plate-

tectonics.html • www.physicalgeography.net/fundamentals/10h.html • www.stemnet.nf.ca/CITE/earthquakes_measurement.htm • www.geo.mtu.edu/UPSeis/waves.html

http://school.discovery.com/lessonplans/programs/earthquakes-gettingready/

• http://volcano.und.nodak.edu/• http://vulcan.wr.usgs.gov/• http://www.geo.mtu.edu/volcanoes/• http://southport.jpl.nasa.gov/volcanopic.html• http://mcps.k12.md.us/departments/eventscience/

ebs.Volcano.html