Presentation on theme: "The Earth is divided into layers by density. As the Earth solidified during the formation of the solar system elements with higher density were drawn."— Presentation transcript:
The Earth is divided into layers by density. As the Earth solidified during the formation of the solar system elements with higher density were drawn toward the center of the Earth by gravity.
Oceanic crust is comprised mainly of the rock basalt
Continental crust makes up the land masses. This thicker, less dense material allows the continents to rise above sea level and remain dry for very long periods Continental crust is made primarily of the rock granite
As the very hot core heats the material in the Mantle it causes the material to move in a circular pattern. The mantle material heats up and rises and then cools and sinks. This circular pattern of movement within the mantle (called a convection current) pushes the lithospheric plates as they float. The movement and interaction of these plates causes most of the large scale changes on Earth's surface.
Alfred Wegener a German scientist was the first to propose this theory to the scientific community in the early 1900’s
Pangea was the name for this supercontinent that began to break up about 200 million years ago
Wegener’s theories were not accepted at the time because his explanations were not supported by physicists
His explanation for movement was that the continents plowed through the seafloor crust like moving islands
His explanation for the reason why the continents moved was the spinning of the earth
Although his explanations for the reason the continents drifted were incorrect there was still convincing evidence that they were indeed once together.
Rock formations in the Appalachian Mountains matched up with ones in Greenland.
Fossil evidence found in South America and Africa were especially strong
Bones from the Mesosaurus and Kannemeyerid were found in the same rock formations in Brazil and Chad
Even glacial striations from ancient Ice ages were found to match perfectly
Climatic evidence found that there were coal deposits in Antarctica suggesting that continent was at one time much closer to the equator
In the early 1960’s new evidence revealed the process on how the continents could indeed move
Advances in sonar technology in the 1940’s and 50’s allowed us to begin to accurately map the seafloor
This evidence proved that the seafloor was not flat and featureless as once thought. Vast underwater mountain chains and deep trenches were discovered.
Earthquakes and volcanic activity was prevalent in certain parts and missing in others
The ocean floor was found to be much younger than the continental crust
The thickness of the layers of sediments increased with the distance on either side of the ocean ridges
Once scientists were able to bring sea floor samples to the surface they were able to determine that a record of the seafloor was being kept by Earth’s magnetic field
Paleomagnetism is the study of this magnetic record using data gathered from iron-bearing minerals
The magnetic records for the seafloor on either side of the mid-ocean ridges matched perfectly showing that the seafloor was growing outward from the ridges in both directions
Theory of Plate Tectonics states that the Earth’s crust and rigid upper mantle are broken into enormous slabs called plates.
There are 17 known plates
The plates do not remain still. They slide across the partially molten mantle material of the asthenosphere as a result of convection currents deep in the Earth’s interior.
Tectonic plates interact at places called plate boundaries.
Typically, since the Earth is spherical the plate boundaries would appear as the threads of a baseball weaving through the mid-ocean rifts and around the smaller plates.
Notice that ALL of the major plates include both continental and oceanic crust
Some plates move towards each other, some move away, and some slide horizontally past each other. Each interaction results in geologic process and characteristics that we can now associate with it.
Divergent boundaries are places where tectonic plates are moving apart
Most divergent boundaries are found on the seafloor where they form mid-ocean ridges
Iceland is a continuation of the Atlantic mid- ocean ridge
The Arabian Peninsula is an example of a newly formed divergent boundary as it separates from the rest of Africa
Convergent boundaries are where plates move toward each other. These boundaries give us the most interesting geologic features. There are three types of convergent boundaries
Oceanic crust to oceanic crust results in the subduction of one of the two plates and an island arc
Subduction is the process of one plate descending beneath the other
The Phillippines are a noticeable example
Oceanic to continental convergence also results in the subduction of the oceanic crust
A volcanic mountain range such as the western portions of North and South America is the result
The oceanic crust always subducts because it is denser than continental crust
Continental to continental convergence results in folded mountains
The Himilayas are an active folded mountain chain
Transform boundaries occur where plates slide horizontally past each other. They rarely are seen on the continents however the San Andreas Fault in California is an exception
Most earthquakes occur when rocks fracture deep within the Earth
Compression decreases the volume of a material
Tension pulls the material apart
Shear causes a material to twist
The vibrations in the ground during an earthquake are called seismic waves
Primary Waves (P-waves) squeeze and pull rocks in the same direction along which the waves are traveling
P-waves travel the fastest and CAN travel through liquids
Secondary Waves (S-waves) cause rocks to move at right angles to the direction of travel
S-waves travel slower than P-waves and CANNOT travel through liquids
Surface Waves (L-waves) travel only on the surface in two directions causing an up-and- down and side-to side motion
Most of the damage we see on the surface from earthquakes is caused by surface waves
Most of our knowledge of Earth’s interior comes from the study of seismic waves. The relationship between P-waves and S-waves allows us to measure the size of the inner and outer cores
More than one million earthquakes occur each year. More than 90 percent of these are not even felt by humans.
Magnitude is the amount of energy released by an earthquake
Richter Scale is the numerical scale to measure magnitude based on the size of the largest seismic waves generated
Each number on the Richter scale represents an increase in amplitude by a factor of 10
8 is ten times the amplitude of 7
Modified Mercalli Scale measures the amount of damage done by the earthquake in Roman numerals I - - X II
Earthquakes are located by tracking the seismic waves registered at different locations and plotting circles based on the speed of the waves and time elapsed
Seismometers are sensitive instruments used to detect and record even the slightest vibrations of the earth’s surface
Focus is the point of initial fault rupture and the location where the earthquake originates
Epicenter is the point on the surface directly above the focus Focus is the point of initial fault rupture and the location where the earthquake originates