Inside Planet Earth

Inside Planet Earth

Alfred Wegener and Continental Drift<= /b>

It has taken a long time t= o learn what we know about the inside of Earth.&nb= sp; Alfred Wegener was a Ge= rman scientist that was interested in the continents. In the early 1900’s, he hypothesized that the continents had moved over time and they were once joi= ned together as a single continent. This idea became known as c= ontinental drift. The super continen= t was called Pangaea which means “all lands.” Alfr= ed Wegener studied land features, fossils, and climate change evidence to support the = idea of continental drift. Wegener= found that mountain ranges in Africa and South America lined up. Wegener found that fossils in rocks in Africa, South America,= Australia, India, and Antarctica matched. As Pangaea broke apart and moved, = some continents moved toward the equator and became warmer as other continents m= oved towards the poles and became colder. Wegener found the fossils of tropical plants in the Arctic region. Wegener believed this land must ha= ve been located near the equator in the past.= Wegener died in 1930 without being able to provide science with a mechanism for the pushing and pulling of the continents. He could not provide science with = the cause of continental drift and science rejected his idea.=

Harry Hess and Sea-Floor Spreading

There are many mid-ocean r= idges beneath Earth’s oceans. Sonar was used to map the mid-ocean ridges. An American geologist named Harry Hess studied maps of the mid-ocean ridges. Harry Hess started to think that A= lfred Wegener was correct and suggested that the cause was sea-floor spreading. This was the process of the sea floor spreading apart on both sides = of the mid-ocean ridge where new crust is being added. This movement would carry the cont= inents along with the ocean floor. R= ock evidence in the ocean supported this idea of molten material erupting and hardening quickly under water forming rocks. More evidence was provided from the rocks formed by Earth’s magnetic field when normal and when the field= was reversed. It was also found t= hat rocks farther away from the ridge are older than rocks nearer the ridge. Science now had a mechanism to sup= port continental drift through sea-floor spreading. Where does the new crust end up? Over many millions of years, the o= cean floor sinks back into the mantle. This happens at deep-ocean trenches and is called subduct= ion. Subduction in the Pacific Ocea= n is occurring faster than new crust is added and the result is that width of th= e Pacific Ocean will shrink. In the Atla= ntic Ocean, it is the opposite.&nb= sp; There are only a few short trenches. The ocean crust is attached to the continental crust. As sea-flo= or spreading continues which no place to go, the continents move with it.

J. Tuzo Wilson and Plate Tectonics

http= ://geology.csupomona.edu/drjessey/class/Gsc101/Plate.html

The work of Alfred Wegner = and Harry Hess continued with the Canadian scientist J. Tuzo Wilson. He believed the lithosphere was broken into section called plates that fit together. Wilson put the information about continental drift, sea-floor spreading and plates together to form a scientific theory which explained a range of observations. This story brin= gs us to 1965.

The theory of plate tectonics explains the formation, movement, and subduction of Earth’s plates. The theory states that pieces of the lithosphere are in slow, consta= nt motion, driven by convection currents in the mantle. Plate boundaries are where edges of Earth’s plates come together. The three types of plate boundaries are divergent boundaries, convergent boundaries, and transform boundari= es.

Divergent boundaries are where two plates move apart or diverge. This takes place in the ocean where sea-floor spreading occurs. T= his also takes place on land producing a deep valley called a rift valley.=

Convergent boundaries are where two plates come together and collide. Density is the factor determining = which plate moves up and which plate moves down.= When two ocean plates meet at a trench, the denser plate is sinks beneath the other. When an oc= ean plate collides with a continental plate, the ocean plate, being denser than= the continental plate, sinks beneath the continental plate so subduction occurs. When two continental = plates collide, they are squeezed into mountains and mountain ranges as the plates= are not dense enough to sink very far into the mantle.

Transform boundaries are where two plates slip past each other as they are moving is opposite directions. This is an area of earthquake activity.

Forces Within the Earth

There are forces within th= e Earth that push and pull on the Earth’s crust which is the outer most layer= of the Earth. The crust includes= that continental crust and the oceanic crust. The stress of pushing and pulling on the crust changes the shape an= d volume of the rocks of the crust. The rocks are deformed as they break, fracture, crack, tilt, and fold.

The three types of stress are compression, tension, and shearing. Compression squeezes rocks together until they fold or break. Tension pulls on the crust stretch= ing the rock. Shearing pushes roc= ks in the crust in opposite directions which tears and twists the rocks. These fo= rces have changed the shape and volume of rock over millions of years.

When stress causes rocks t= o break, the area of the break or the crack is called a fault. There are different types of faults. Mo= st faults occur along plate boundaries.

Normal faults = are caused by tension pulling rock apart. The hanging wall slips down relative = to the footwall.

Reverse faults occur where rock is pushed together and compressed. The hanging wall moves up relative= to the footwall.

Strike-slip faults occur where plates move past each other in opposite directions with little up or = down motion. A strike-slip fault that forms a boundary between two plates is a transform boundary. The San A= ndreas fault in California is a strike-slip fault that is also a transform boundary. The rocks on each side of a strike= -slip fault slip past each other.

Anticlines, Synclines, Folded Mountains, Fault-block Mountains and Plateaus

An Anticline is a fold in rock that bends up into an arch. A Syncline is a fold in rock that bends down to form a valley. Compression forces folding the cru= st form anticlines and synclines form folded mountains made of anticlines and synclines. Fault-block mountains form from two normal faults cutting through a block of rock. = Tension moves two plates away from each other leaving a block of rock between them. When the hanging wall o= f each normal fault slips down, the block in between moves up and forms a fault-bl= ock mountain. When a large area o= f flat land is elevated high above sea level, it is called a plateau. An examp= le is the Colorado Plateau which is 1500 meter above sea level. http://www.adlc.ca/home/stuWork/sampleLessons/Science24/lesson2-5.htm
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Earthquakes=

Rock moving beneath the Earth’s surface causes shaking and trembling. This is called an earthquake. The area beneath the Earth’s surface where the stressed rock breaks, triggering the earthquake, is called the focus. The point on the Earth’s sur= face that is directly above the quake focus is the epicenter. Seismic waves move out in all directions from the focus carrying energy away from t= he focus. The main three types of seismic waves are P waves, S waves and surface waves. P waves compress and expand like an accordion vibrating the crust and move through solids and liquids. P= waves are the fastest and arrive first. S waves vibrate in two directions= : side to side and up and down throu= gh solids only shaking them violently. S waves arrive soon after P waves. = Surface waves produce ground movements in s wave like motion or rolling motion. Surface waves show the largest disturbance on a seismogram. Earthquakes are measured by the Me= rcalli Scale, the Richter Scale, and the Moment Magnitude Scale. Earthquake damage includes shaking, liquefaction, aftershocks, and tsunamis. Liquefaction turns loose, soft soil into liquid mud in places where soil contains a lot = of moisture. Aftershocks occur h= our, days, weeks, or months after the original earthquake. Tsunamis are caused by earthquakes on the ocean floor displacing water and forming l= arge waves spreading out and speeding across the ocean turning into mountains of water as the tsunami nears shallow water.

Volcanoes and Plate Boundaries

A volcano is a spot in the crust that is weak allowing molten material or magma to come to the surface.&= nbsp; Magma is a mixture of r= ock substances, gases, and water coming from the mantle as a molten mixture. Lava is magma that has reached the surface.= Lava cools and forms solid rock.&nb= sp;

Volcanoes are everywhere o= n land and beneath the sea. The Ring of Fire is a major volcano b= elt in the Pacific Ocean. These volcano belts form near the = plate boundaries as pieces of crust pull apart (diverge) or push together (converge). This cracks the c= rust and allows magma to come to the surface.&n= bsp;

Divergent Boundaries: The mid-ocean ridge is a dive= rgent plate boundary where lava pours out of the rift valley cracks building mountains over time. Volcanoe= s also form on land at divergent plate boundaries such as the Great Rift Valley in= East Africa.

Convergent Boundaries: Volcanoes occur often where t= wo ocean plates collide or where an ocean plate collides with a continental plate. In each case, the ocean plate sinks beneath the trench. Rock above the plate melts into magma and under pressure erupts to t= he surface as lava. This process returns ocean plates to the mantle through subduction as the denser, older plate sinks. Examples of ocean plates colliding are Japan, New Zealand, and the Caribbean Islands. Examples of ocean plates subducted beneath continental plates are the Andes Mountains volcanoes and the Pacific Northwest volcanoes.

There are hot spots in the Earth’s mantle. Volcanoes form above the hot spot = where magma erupts through the crust and reaches the surface. Hot spots can be in the middle of a plate or near a plate boundary. The Hawaiian Islands formed as the Pacific plate moved over a hot spot. This took place over millions of y= ears to form the islands. There ar= e also hot spots under the continents= . The North American Plate has a hot= spot located in Wyoming at Yellow Stone National Park.=

Magma and Volcanoes

The viscosity of magma dep= ends on its silica content and temperature. The greater the viscosity of the liquid the slower it flows. Silica is made of the elements sil= icon and oxygen. 50 to 70% of magm= a is silica. Magma with a lot of s= ilica is light-colored lava that is too sticky to flow far. This magma forms rhyolite with a composition like granite. Mag= ma with less silica has low viscosity as it flows easily and produces a dark colored lava cooling and forming rocks like basalt. Temperature affects lava viscosity= . Pahoehoe lava moves fast as a hot low viscosity lava forming solid masses of wrinkles, pillows, and ropelike coils.&nbs= p; Cooler slower moving lava with higher viscosity is called aa cools and hardens into rough j= agged lava chunks.



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Magma collects in a magma chamber beneath a volcano. A long tube in the ground connecting the magma chamber to the Earth’s surface is called a pipe through which the magma moves upward reaching the = vent of the volcano where the mol= ten rock and gas leave the volcano. Volcanoes have a central vent at the top and other vents on the sides. The area covered by la= va is called the lava flow. A bowl = shaped area at the top of a volcano is called the crater. Dissolved gases are trapped in the= magma and under great pressure. As = the magma rises, the pressure of the surrounding rock in the magna decreases. The dissolved gases expand and bub= bles form. As pressure falls, the = size of the bubbles increases. The expanding gases are an enormous force.&nbs= p; Magma is pushed from the chamber up the pipe where it flows or explo= des out of the vent as lava.

Volcano Eruptions

Quiet Eruptio= ns occur when magma is low in silica, low in viscosity and flows easily producing Pahoehoe or aa. An example is Mount Kilauea. Explosive Eruptions occur when magma is high in silica, high in viscosity, and is thick and sticky. Trapped gas= es build up until they explode. = The erupting gases and steam push the magma out of the volcano with tremendous force. An Example is Mount St. Helens.&= nbsp; Lava breaks into fragments cooling quickly into different sizes:

Volcanic ash<= /b>: fine, rocky particles as small as = dust

Cinders:<= span style=3D'mso-spacerun:yes'> pebble sized particles

Bombs: larger pieces from baseball to car= size

Pyroclastic f= low: an explosive eruption hurling out = hot gases, ash, cinders, and bombs

Obsidian: forms from lava that cools qui= ckly becoming smooth, and glasslike

Pumice: forms when gases are trapped in fa= st cooling lava leaving spaces in the rock like
        =         the holes in break or cake.

Volcano Life Cycle

The stages of volcano acti= vity are describes as active, dormant, or extinct.&= nbsp; A dormant volcano is ex= pected to become active sometime in the future.&n= bsp; An extinct volcano is unlikely ever to erupt again. An active volcano is a volcano that = is erupting or shows signs that it may erupt in the near future. Geologists use tiltmeters along wi= th other scientific instruments to detect slight surface changes in elevation = and tilt resulting from magma moving underground

Volcanic Landforms:&nb= sp; Types of Volcanoes

Volcanoes make landforms f= rom lava, ash and other materials. This includes shield volcanoes, cinder cone volcanoes, composite volcanoes, and = lava plateaus. A wide gentle slopi= ng mountain called a shield volcano, forms from thin layers of lava hardening on top of each other building up.<= span style=3D'mso-spacerun:yes'> The Hawaiian Islands rising from a hot spot are shield volcanoes. Cinder cone volcanoes

form as high viscosity lava produces ash, cinders, and bombs that build up around the vent in a steep c= one shaped mountain. Composite volcanoes are tall and = coned shaped with layers of alternate lava flows of ash, cinder, and bombs. An example is Mount St. Helens and= Mount Fuji. = Lava Plateaus forms when lava flo= ws out of several cracks in an area and the thin runny lava travels far before cooling. This happens over and over. Millions of years later= these layers form high plateaus. An example is the Columbian Plateau in Washington, Oregon, and Idaho. A huge hole left by the collapse o= f a volcano is called a caldera. Here the mountain becomes hollow a= nd collapses inward with nothing to support it. Lake Caldera in Oregon is an example. Over time it filled with water fro= m rain and snow. Lava and ash breakd= own over time from weathering and form soil rich is nutrient compounds needed by plants to support growth and development.&= nbsp;

Magma Landforms<= o:p>

Some magma never reaches t= he surface and hardens beneath the surface forming volcanic necks, dikes and s= ills and over time due to weathering the hardened magma then becomes exposed.

Volcanic necks look like giant teeth in the ground which formed when magma hardened in a volcano pipe. The rock around the pipe wears away and exposes the hard rock neck.

A dike is magma that forces itself across rock layers and hardens= .

A sill is magma that is squeezed between horizontal layers of roc= k.

A batholith is a mass of rock formed when a large body of magma c= ools inside the crust and then is exposed when the layers of rock around it have worn away.

A dome mountain forms when uplift pushes a batholith or smaller b= ody of hardened magma toward the surface. This process formed the Black Hills of South Dakota.

Geothermal Activity

Magma beneath the surface = heats underground water creating geysers and hot springs usually occurring in areas of present or p= ast volcanic activity. = Hot springs are natural pools heated by a nearby b= ody of magma or hot rock deep underground.&nbs= p; Geysers are fountains of water and steam erupting from the ground as rising hot water and steam beco= me trapped underground in a narrow crack building pressure until it suddenly sprays above the surface as a geyser.