Plate Tectonics

Plate Tectonics

Continental Drift Alfred Wegner—1st to propose the theory of continental drift His theory– Continents were once a single landmass then, over time, they broke up and drifted to where they are today

Wegner’s Evidence of Continental Drift Fossil Evidence Rock formations Climatic Evidence Geographic Evidence

Fossil Evidence

Let’s do a puzzle! Fossil puzzle…match up the fossils on the continents to view Wegner’s evidence of continental drift

Rock Formations Just like fossils, similar rock formations were found on different continents

Climatic Evidence Shows that land used to have different climates than is natural to have in the current position of the land Example: Tropical plant fossils were found in Antarctica

Geographic Evidence Shapes of continents look like they fit together and have similar geographical features

FYI *As continents rift or as mountains form, populations of organisms are separated. When populations of organisms are separated, new species may evolve from existing species. *Similar rock formations and fossil evidence supported Wegener’s evidence.

Mid-Ocean Ridges --a place where crust is spreading an creating new ocean floor --a place where old crust is recycled (this process makes oceanic crust younger than continental crust)

Lets make a mid-ocean ridge! ACTIVITY!!!!!!!!! Lets make a mid-ocean ridge!

Sea-Floor Spreading Harry Hess hypothesized that the valley at the center of mid-ocean ridges was a crack in the Earth’s crust At this crack, magma rises up to form new sea floor which cools and forms new sea flooring This process is known as sea-floor spreading

Layers of our Planet

Layers of our Planet Lithosphere – the solid, outer layer of Earth that consists of the crust and the rigid upper part of the mantle Asthenosphere – The solid, plastic or putty-like layer of the mantle beneath the lithosphere. Made of mantle rock that flows very slowly, which allows tectonic plates to move on top of it

Theory of Plate Tectonics This is the theory that explains how large pieces of lithosphere called plates, move and change shape

Tectonic Plates Scientists have identified about 15 major plates:

Plate Tectonics Activity

Types of Plate Boundaries

Divergent Boundaries These types of boundaries move AWAY from each other Examples: Mid-ocean rifts, the Red Sea (between the African and Arabian Plates)

Convergent Boundaries Plates collide together at these types of boundaries Examples: Areas of subduction Mountain ranges Ocean trenches trench

Transform Boundaries A boundary at which two plates slide past each other horizontally Example: San Andreas Fault in California

The Supercontinent Cycle The process by which supercontinents form and break apart This happens because tectonic plates of the Earth are always moving, though very slowly

450 Million Years ago Near the end of the Precambrian time Earth’s continents were separated…not as much land was above water as today

250 Million Years Ago By the end of the Permian Period, Pangaea had formed

150 Million Years Ago Pangaea had split into two continents, Laurasia and Gondwanaland

60 Million Years Ago Continents were moving toward their current positions on Earth

Future? Scientist propose that in about 250 million years the earth might look like this:

Earthquakes

What is an Earthquake? Earthquake--Occur when rocks under stress shift along a fault (energy released) Fault—break in rock where one block moves relative to another

Let’s Build a Fault Model!

Damage from Northridge Earthquake in Southern California--1994

Anatomy of an Earthquake Focus--1st motion of earthquake in Earth, along fault Epicenter—point on Earth’s surface directly above focus 90% of continental earthquakes have shallow focus—most damaging

Parts of an Earthquake

Elastic Rebound Elastic Rebound—sudden return of deformed rock to undeformed shape Elastic rebound causes earthquakes

Fence offset due to Elastic Rebound

Seismic Waves When rocks on a fault move, they release energy as seismic waves Seismic waves travel outward from the focus in all directions

Body wave—seismic wave that travels thru a medium two types: P-wave & S-wave

Seismic Waves P (primary) waves are the fastest & travel thru solids, liquids, & gases

Seismic Waves S (secondary) waves are 2nd fastest & travel thru solids only. Although slower they can cause the most damage

Seismic Waves Surface wave— a seismic wave that travels along surface of medium. These are S & P waves that reach the surface & can cause greatest damage

Water Wave and Slinky Activities!

WAYS TO MEASURE AN EARTHQUAKE There are two major scales to measure an earthquake: Mercalli Scale: measures earthquake intensity (by amount of damage caused) Richter Scale: measures earthquake magnitude (strength)

Studying Earthquakes Seismology—study of earthquakes & seismic waves Seismograph—records vibrations in ground Seismogram—tracing of EQ motion, recorded by seismograph

Bill Nye on the Richter Scale http://www. youtube. com/watch Bill Nye on the Richter Scale http://www.youtube.com/watch?v=1qbg7orb1lc Bill Nye on Waves Earthquake recording station/seismograph clip http://www.youtube.com/watch?v=dx4OqT0PYnU&lr=1

SEISMOGRAM Order of recording: P-waves, S- waves, then surface waves Shows S-P lag time

P-Wave S-Wave S-Wave S-Wave To find S-P lag time, subtract where the P wave starts from where the S wave starts (S-P = Lag Time)

What is S-P lag time for San Francisco, CA? What is S-P lag time for El Paso,TX? 28 sec – 0 sec = 28 sec lag time What is S-P lag time for San Francisco, CA? 120 sec – 0 sec = 120 sec lag time What is S-P lag time for Seattle, WA? 165 sec – 0 sec = 165 sec lag time Which city is closest to the epicenter? The city with the shortest lag time is closest to the epicenter, so it’s El Paso, TX

Locating Earthquakes Through Triangulation S-P lag times are analyzed to find the epicenter of Earthquakes using 3 stations Why 3 stations? Because all we know is distance, so it takes 3 circles to narrow it down to one point Epicenter

Let’s stop here and practice finding S P lag time

Fault Zones Fault zone—region w/ lots of faults that typically form at plate boundaries Fault zones and earthquakes can occur away from plate boundaries as well

Fault Zones—New Madrid New Madrid fault line—New Madrid, MO—120 miles southward on I-55 1811/1812—most widely felt series of E.Q. in U.S. history (2000+) Five were 8.0+ Ancient fault zone deep in crust of Mississippi River region

Tsunamis Tsunami—giant ocean wave that forms after volcanic eruption, submarine earthquake or landslide May form when ocean floor rises due to earthquake Tsunami animation http://embc.gov.bc.ca/em/tsunamis/causes_2.htm

Japan’s Tsunami Before and After…(Google Earth)

Volcanoes Erupting with fun!

Magma vs. Lava Magma is liquid rock produced under the Earth’s surface but Magma becomes Lava as soon as it leaves the Earth and flows outside. Lava Magma

Magma Magma can form under three conditions: 1. If rock temperature rises above its melting point then it will melt into magma 2. Rock can melt when too much pressure is removed from rock that is above its melting point 3. The addition of fluids, such as water, may lower the melting point of some rock and cause it to melt

Volcanism Volcanism is any activity that includes the movement of magma onto Earth’s surface A volcano is a vent or fissure in Earth’s surface through which magma and gases are expelled

Location and Formation Of Volcanoes Most volcanoes occur in convergent and divergent boundaries of tectonic plates A major zone of active volcanoes is located in the “Pacific Ring of Fire” which is also a major earthquake zone

Locations of Volcanoes Some tectonic boundaries include: Subduction Zones Mid-Ocean Ridges Hot Spots

A subduction zone is where one tectonic plate moves under another Subduction Zones A subduction zone is where one tectonic plate moves under another

Mid-Ocean Ridges A long, undersea mountain chain that has a steep, narrow valley at its center. Forms as magma rises from the asthenosphere Creates new ocean floor as tectonic plates move apart (sea floor spreading)

Hot Spots Areas of volcanism within the interiors of lithospheric plates The Hawaiian Islands were created by a hot spot See HOT demo!

Types of Volcanic Eruptions Quiet volcanoes have mafic magma which is rich in magnesium and iron. Mafic magma is dark in color with runny lava Explosive volcanoes have felsic magma which is rich in light-colored silicate materials and is thick and sticky. Compare water boiling (quiet volcano) to thick spaghetti sauce boiling (explosive volcano)

Pyroclastic Materials “Pyro” means fire Pyroclastic materials include fragments of rock that form during volcanic eruptions

Types of Pyroclastic Materials (from smallest to largest Volcanic dust Volcanic ash Lapilli—means little stones…they normally fall near the vent Volcanic bombs—clots of lava that are thrown out of the volcano & become round or spindle shaped as they go through the air Volcanic blocks—solid rock that is blasted through the vent…some are as big as a house!!

Read “What Volcanoes Can Produce”

Types of Volcanoes Shield volcanoes Cinder Cones Composite Volcanoes (Stratovolcanoes) Calderas

Shield Volcanoes Wide base Gently sloping sides Forms from quiet eruptions

Cinder Cone Volcanoes Steep slopes Form from explosive eruptions and are made of pyroclastic materials

Composite Volcanoes (Stratovolcanoes) Made with alternating layers of hardened lava flows and pyroclastic materials This type of volcano alternates quiet and explosive eruptions

Calderas This type of volcano is created when the magma chamber below a volcano empties and the cone collapses The collapse leaves a large basin-shaped depression (crater) Some calderas eventually fill with water to become lakes

Read “What Are Volcanoes?” and answer questions