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Earth's Internal Processes
Transcript of Earth's Internal Processes
Evidence/Failing of the Continental Drift Hypothesis
-In 1915, Alfred Wegner proposed a hypothesis that all the continents were once part of a super continent called Pangea.
-At the time it was not accepted, but now we have evidence such as coastlines vs. continental shelves, fossils, and matching rock layers to help prove the hypothesis true.
How This Links to Plate Tectonics
-More evidence of seafloor spreading comes from the study of magnetic properties of seafloor rocks.
-After all this had been discovered, the 1960's geological data led to the Theory of Plate Tectonics.
Characteristics Of Earthquakes
-In every earthquake there are three different waves that are sent out. P-waves, S-waves, and Surface Waves.
-P-waves, or primary waves, travel the fastest. They are a type of compressional wave.
-S-waves, or secondary waves, arrive after P-waves. They travel in an up and down motion.
-Surface waves travel in a more complex manner. They often travel in a rolling motion like waves, but can also travel in an up and down and side to side motion. This causes a lot of damage.
The Cause of Earthquakes
-Earthquakes do not occur randomly. They are found in defined zones located at plate boundaries.
-Earthquakes are caused by forces that act on the rocks. There are 4 types of stresses that cause this.
The Pattern of Occurance of Volcanoes & It's Link to Plate Tectonics
How Scientists Infer the Earth's Interior
-Geologists use seismic waves to study the Earth's interior.
-Seismic waves change direction and intensity as they move through Earth's interior.
-The speed and direction of seismic waves change when the properties of the materials in which they move change.
By: Amanda Nielson
-However there was not enough evidence to thoroughly support the idea of Continental drift at the time.
-After WWII a man named Harry Hess used sonar to obtain accurate maps of the ocean floor. He found a feature called the Mid Ocean Ridge.
-Harry Hess developed a theory of Sea floor spreading, and once he found that the oldest rocks are nearest the continents and the youngest are by the MOR, this continued to support that theory.
-This theory states that the Earth's surface is made of separate "slabs" called plates.
The four types of stresses are:
(Squeezed or shortened)
(Stretched or lengthened)
(Moved in different directions along a plain)
-When a rock is deformed along cracks in the Earth's crust, strain energy builds up in the rocks. When energy is released, the rock moves. The sudden release of strain energy when the rock moves along a fault is called elastic rebound. This produces seismic waves.
-Try this quiz to test your knowledge on Earthquakes:
"PRISMS: Phenomena & Representation for Instruction of Science in Middle School." PRISMS: Tectonic Plates, Earthquakes, and Volcanoes. Web. 19 May 2014.
"Reasons Why Earthquakes and Volcanoes Occur Where They Do - My Revision Site." Reasons Why Earthquakes and Volcanoes Occur Where They Do - My Revision Site. Web. 19 May 2014.
Brennan, John. "What Is the Difference Between the Focus & the Epicenter of an Earthquake?" EHow. Demand Media, 12 June 2011. Web. 19 May 2014.
-Due to refraction of P-waves in the outer core and the fact that S-waves can only travel through solids, there is an area that receives no seismic waves from any given earthquake.
-Scientists infer about Earth's deep interior based on the previous information and what they know about the structural layers of Earth, which include: Lithosphere, Asthenosphere, Lower Mantle, Outer Core, Inner Core.
-Watch this video that covers how scientists infer about Earth's deep interior.
-A volcano is formed where the magma reaches the Earth's surface.
-Most of the eruptions occur at hotspots and plate boundaries. Hot spots are places on the mantle where the temperature is high enough to form magma.
-When volcanoes occur at plate boundaries, that is when plate tectonics comes in.
-Volcanoes occur at convergent and divergent plate boundaries. (excluding continental and continental convergent plates)
-Volcanoes are also found along "The Ring of Fire"
-The focus of an earthquake is the point where the fault ruptures to cause the earthquake.
-The epicenter is the place on ground located directly above the focus which helps people detect where exactly an earthquake began. This is helpful in finding out as much as we can about the origin and magnitude of the earthquake.
-There are two different scales that can also give us information on the earthquake.
-The Modified Mercalli Scale ranks earthquakes on the amount of damage they cause.
-This scale ranges from I to XII
-The Richter Scale measures the amount of energy during an earthquake.
-A device called a seismograph records the vibrations produced by an earthquake.
-Take this quiz to see what facts you know about earthquakes: