PLATE TECTONICS

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.

EARTH’S CRUST Oceanic crust is comprised mainly of

the rock basalt

EARTH’S CRUST 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.

CONTINENTAL DRIFT Alfred Wegener a German scientist was

the first to propose this theory to the scientific community in the early 1900’s

CONTINENTAL DRIFT Pangea was the name for this

supercontinent that began to break up about 200 million years ago

CONTINENTAL DRIFT Wegener’s theories were not accepted

at the time because his explanations were not supported by physicists

CONTINENTAL DRIFT His explanation for movement was that

the continents plowed through the seafloor crust like moving islands

CONTINENTAL DRIFT His explanation for the reason why the

continents moved was the spinning of the earth

EVIDENCE OF CONTINENTAL DRIFT Although his explanations for the

reason the continents drifted were incorrect there was still convincing evidence that they were indeed once together.

EVIDENCE OF CONTINENTAL DRIFT Rock formations in the Appalachian

Mountains matched up with ones in Greenland.

EVIDENCE OF CONTINENTAL DRIFT Fossil evidence found in South America

and Africa were especially strong

EVIDENCE OF CONTINENTAL DRIFT Bones from the Mesosaurus and

Kannemeyerid were found in the same rock formations in Brazil and Chad

EVIDENCE OF CONTINENTAL DRIFT Even glacial striations from ancient Ice

ages were found to match perfectly

EVIDENCE OF CONTINENTAL DRIFT Climatic evidence found that there

were coal deposits in Antarctica suggesting that continent was at one time much closer to the equator

SEA FLOOR SPREADING In the early 1960’s new evidence

revealed the process on how the continents could indeed move

SEA FLOOR SPREADING Advances in sonar technology in the

1940’s and 50’s allowed us to begin to accurately map the seafloor

SEA FLOOR SPREADING This evidence proved that the seafloor

was not flat and featureless as once thought. Vast underwater mountain chains and deep trenches were discovered.

SEA FLOOR SPREADING Earthquakes and volcanic activity was

prevalent in certain parts and missing in others

SEA FLOOR SPREADING The ocean floor was found to be much

younger than the continental crust

SEA FLOOR SPREADING The thickness of the layers of

sediments increased with the distance on either side of the ocean ridges

PALEOMAGNETISM 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 Paleomagnetism is the study of this

magnetic record using data gathered from iron-bearing minerals

PALEOMAGNETISM 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

THE THEORY OF PLATE TECTONICS Theory of Plate Tectonics states that

the Earth’s crust and rigid upper mantle are broken into enormous slabs called plates.

THE THEORY OF PLATE TECTONICS There are 17 known plates

THE THEORY OF PLATE TECTONICS 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.

PLATE BOUNDARIES Tectonic plates interact at places called

plate boundaries.

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.

PLATE BOUNDARIES Notice that ALL of the major plates

include both continental and oceanic crust

PLATE MOTIONS 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.

PLATE MOTIONS Divergent boundaries are places where

tectonic plates are moving apart

PLATE MOTIONS Most divergent boundaries are found

on the seafloor where they form mid-ocean ridges

PLATE MOTIONS Iceland is a continuation of the Atlantic

mid-ocean ridge

PLATE MOTIONS The Arabian Peninsula is an example of

a newly formed divergent boundary as it separates from the rest of Africa

PLATE MOTIONS 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

PLATE MOTIONS Oceanic crust to oceanic crust results

in the subduction of one of the two plates and an island arc

PLATE MOTIONS Subduction is the process of one plate

descending beneath the other

PLATE MOTIONS The Phillippines are a noticeable

example

PLATE MOTIONS Oceanic to continental convergence

also results in the subduction of the oceanic crust

PLATE MOTIONS A volcanic mountain range such as the

western portions of North and South America is the result

PLATE MOTIONS The oceanic crust always subducts

because it is denser than continental crust

PLATE MOTIONS Continental to continental convergence

results in folded mountains

PLATE MOTIONS The Himilayas are an active folded

mountain chain

PLATE MOTIONS 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

EARTHQUAKES Most earthquakes occur when rocks

fracture deep within the Earth

EARTHQUAKES Compression decreases the volume of a

material

EARTHQUAKES Tension pulls the material apart

EARTHQUAKES Shear causes a material to twist

EARTHQUAKES WAVES The vibrations in the ground during an

earthquake are called seismic waves

EARTHQUAKES WAVES Primary Waves (P-waves) squeeze and

pull rocks in the same direction along which the waves are traveling

EARTHQUAKES WAVES P-waves travel the fastest and CAN

travel through liquids

EARTHQUAKES WAVES Secondary Waves (S-waves) cause

rocks to move at right angles to the direction of travel

EARTHQUAKES WAVES S-waves travel slower than P-waves

and CANNOT travel through liquids

EARTHQUAKES WAVES Surface Waves (L-waves) travel only on

the surface in two directions causing an up-and-down and side-to side motion

EARTHQUAKES WAVES Most of the damage we see on the

surface from earthquakes is caused by surface waves

EARTHQUAKES 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

MEASURING AND LOCATING EARTHQUAKES More than one million earthquakes

occur each year. More than 90 percent of these are not even felt by humans.

MEASURING AND LOCATING EARTHQUAKES Magnitude is the amount of energy

released by an earthquake

MEASURING AND LOCATING EARTHQUAKES Richter Scale is the numerical scale to

measure magnitude based on the size of the largest seismic waves generated

MEASURING AND LOCATING EARTHQUAKES Each number on the Richter scale

represents an increase in amplitude by a factor of 10

MEASURING AND LOCATING EARTHQUAKES 8 is ten times the amplitude of 7

MEASURING AND LOCATING EARTHQUAKES Modified Mercalli Scale measures the

amount of damage done by the earthquake in Roman numerals I - - X II

MEASURING AND LOCATING EARTHQUAKES 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

MEASURING AND LOCATING EARTHQUAKES Seismometers are sensitive

instruments used to detect and record even the slightest vibrations of the earth’s surface

MEASURING AND LOCATING EARTHQUAKES Focus is the point of initial fault rupture

and the location where the earthquake originates

MEASURING AND LOCATING EARTHQUAKES 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