Plate Plate TectonicsTectonics

Drifting continents:Drifting continents:

Theory of Continental DriftTheory of Continental Drift

Alfred Wegener suggested that all Alfred Wegener suggested that all continents were joined together at continents were joined together at some time in the past. This is called some time in the past. This is called the hypothesis of “the hypothesis of “continental drift”continental drift”..

According to continental drift, According to continental drift, continents have moved slowly to their continents have moved slowly to their current locations.current locations.

He called this large landmass as He called this large landmass as PangaeaPangaea (“all land”) (“all land”)

EvidenceEvidence1. Landforms

2. Fossils

3. Evidence from climate changing

LandformsLandforms

• Mountains in South Africa line up with mountains in Argentina

• Coal mines line up on different continents

Mountain StructuresMountain Structures Similar rock structures are Similar rock structures are

found on different continents. found on different continents.

For example, parts of For example, parts of Appalachian mountains are Appalachian mountains are similar to those found in similar to those found in Greenland and western Europe. Greenland and western Europe.

Appalachian Mountains strike through the eastern United States and Canada then end at the sea off of Newfoundland.

The Caledonides Mountains are found in eastern Greenland, Ireland, Great Britain and Norway.

These two mountain ranges are the same age with the same rock types and structures.

Besides the puzzlelike fit of continents, fossils provided Besides the puzzlelike fit of continents, fossils provided support for continental drift.support for continental drift.

For example: fossils of the reptile For example: fossils of the reptile MesosaurusMesosaurus have have been found in South America and Africa. been found in South America and Africa.

FossilsFossils

Another fossil that supports the continental drift is Glossopteris which has been found in Africa, Australia, India, South America, and Antarctica.

Climate Clues Climate Clues

Fossils of tropical plants were found in Spitsbergen, Fossils of tropical plants were found in Spitsbergen, an ice covered island in the Arctic Ocean (north of an ice covered island in the Arctic Ocean (north of Norway). Norway).

Glacier ActivityGlacier Activity Glacial deposits and rock Glacial deposits and rock

surfaces scoured and polished by surfaces scoured and polished by glaciers are found in South glaciers are found in South America, Africa, India and America, Africa, India and Australia. Australia.

Why was it not accepted?Why was it not accepted?

Wegener could not provide an adequate Wegener could not provide an adequate explanation for the force that pushes or pulls explanation for the force that pushes or pulls the continents.the continents.

Although Wegener provided evidence to support his Although Wegener provided evidence to support his hypothesis, he couldn’t answer two questions:hypothesis, he couldn’t answer two questions:

1. What was causing the continents to move?1. What was causing the continents to move?Wegener said that this force might be the rotation of EarthWegener said that this force might be the rotation of Earth, , however, physicists were able to show that this force was not however, physicists were able to show that this force was not great enough to move continents.great enough to move continents.

2. How were the continents moving?2. How were the continents moving?Wegener proposed that the continents were Wegener proposed that the continents were plowing through a stationary ocean floor. plowing through a stationary ocean floor. But, his But, his peers argued that continents could not push through peers argued that continents could not push through the ocean floor without fracturing, because crustal the ocean floor without fracturing, because crustal rock is too brittle. And no evidence of fracturing had rock is too brittle. And no evidence of fracturing had been found.been found.

And the rest of the story….And the rest of the story….Undaunted by rejection, Wegener devoted the rest of his life to doggedly pursuing additional evidence to defend his theory. He froze to death in 1930 during an expedition crossing the Greenland ice cap, but the controversy he spawned raged on. However, after his death, new evidence from ocean floor exploration and other studies rekindled interest in Wegener's theory, ultimately leading to the development of the theory of plate tectonics.

http://bumileluhur.blogspot.com/2011/01/this-dyniamic-earth-story-of-plate.htmlhttp://bumileluhur.blogspot.com/2011/01/this-dyniamic-earth-story-of-plate.html

The controversy continues!The controversy continues!Plate tectonics has proven to be as important to the earth sciences as the discovery of the structure of the atom was to physics and chemistry. Even though the theory of plate tectonics is now widely accepted by the scientific community, aspects of the theory are still being debated today. Ironically, one of the chief outstanding questions is the one Wegener failed to resolve: What is the nature of the forces propelling the plates? Scientists also debate how plate tectonics may have operated (if at all) earlier in the Earth's history and whether similar processes operate, or have ever operated, on other planets in our solar system.

Will you be the one to solve the Will you be the one to solve the mystery?mystery?

Plate TectonicsPlate Tectonics

SSeaflooreafloor S Spreadingpreading

Harry Hess

Mapping The Mapping The Ocean FloorOcean Floor

Scientists began using sound waves on moving ships to map large areas of ocean floor in detail.

Sound waves echo off the ocean bottom – the longer the sound waves take to return to the ship, the deeper the water is.

Mapping the Mid-Ocean RidgeMapping the Mid-Ocean Ridge

Also known as the Mid-Also known as the Mid-Atlantic RidgeAtlantic Ridge

Longest mountain Longest mountain chain in the worldchain in the world

Divided by a trenchDivided by a trench

Most is hundreds of meters under water, but part Most is hundreds of meters under water, but part reaches above the ocean surface.reaches above the ocean surface.

It is almost twice as deep as the Grand Canyon.It is almost twice as deep as the Grand Canyon. Iceland is part of the mid-ocean ridgeIceland is part of the mid-ocean ridge

In the early 1960s, Harry Hess proposed that hot, In the early 1960s, Harry Hess proposed that hot, less dense material below Earth’s crust rises less dense material below Earth’s crust rises toward the surface at the mid-ocean ridges. toward the surface at the mid-ocean ridges. Then, it flows sideways, carrying seafloor away Then, it flows sideways, carrying seafloor away from the ridge in both directions. This theory is from the ridge in both directions. This theory is known “known “seafloor spreadingseafloor spreading”.”.

In 1968, a research ship, In 1968, a research ship, Glomar Challenger, Glomar Challenger, began began gathering rock samples from mid-ocean ridges. gathering rock samples from mid-ocean ridges.

They made a remarkable discovery as they studied the They made a remarkable discovery as they studied the ages of rock samples.ages of rock samples.

The younger rocks are closer to the mid-ocean ridges The younger rocks are closer to the mid-ocean ridges and older rocks are farther from the ridges.and older rocks are farther from the ridges.

Evidence of Sea-Floor SpreadingEvidence of Sea-Floor Spreading Molten Material

Magnetic Stripes

Drilling Samples

Magnetic CluesMagnetic Clues Iron-bearing minerals,

such as magnetite, that are found in the rocks of the seafloor can record Earth’s magnetic field direction when they form.

The magnetic alignment in the rocks reverses back and forth over time in strips parallel to the mid-ocean ridges.

Seafloor Seafloor SpreadingSpreading

Subduction of Deep-Ocean Subduction of Deep-Ocean TrenchesTrenches

Subduction is the process by which the ocean floor sinks beneath a deep-ocean trench and back into the mantle.

Subduction and Earth’s OceanSubduction and Earth’s Ocean

Subduction and sea-floor spreading can change the size and shape of the oceans.

The ocean floor is renewed about every 200 million years.

The Pacific Ocean is shrinking; a trench swallows The Pacific Ocean is shrinking; a trench swallows more oceanic crust than the mid-ocean ridge can more oceanic crust than the mid-ocean ridge can produce.produce.

The Atlantic Ocean is expanding.The Atlantic Ocean is expanding. There are only a few trenches in the Atlantic.There are only a few trenches in the Atlantic. The continental crust is attached to the ocean floor, so

as the Atlantic expands and moves, the continents move with it.

Section 3: Section 3: Theory of Plate TectonicsTheory of Plate Tectonics

In the 1960s, scientists developed a new theory that In the 1960s, scientists developed a new theory that combined continental drift and seafloor spreading .combined continental drift and seafloor spreading .

According to the theory of According to the theory of plate tectonicsplate tectonics, Earth’s , Earth’s crust and part of upper mantle are broken into crust and part of upper mantle are broken into sections. These sections are called plates, move on a sections. These sections are called plates, move on a plastic-like layer of the mantle.plastic-like layer of the mantle.

Where did the theory come Where did the theory come from?from?

J. Tuzo Wilson combined Earth’s plates, J. Tuzo Wilson combined Earth’s plates, continental drift, and sea-floor spreading into a continental drift, and sea-floor spreading into a single theory---PLATE TECTONICSsingle theory---PLATE TECTONICS

A Theory of Plate TectonicsA Theory of Plate Tectonics Plate tectonics states that pieces of Earth’s Plate tectonics states that pieces of Earth’s

lithosphere are in constant, slow motion, driven by lithosphere are in constant, slow motion, driven by convection currents in the mantle, and it explains convection currents in the mantle, and it explains the formation, movement, and subduction of the formation, movement, and subduction of Earth’s plates.Earth’s plates.

Basically….Basically….

The plates on the lithosphere float on the The plates on the lithosphere float on the asthenosphere, convection currents rise in the asthenosphere, convection currents rise in the asthensophere and spread out beneath the asthensophere and spread out beneath the lithosphere.lithosphere.

http://youtu.be/ryrXAGY1dmE

Earth’s crust and a part of upper mantle combined Earth’s crust and a part of upper mantle combined are the are the lithospherelithosphere. . (100km=62 mile thick)(100km=62 mile thick)

The plastic-like layer below the lithosphere is The plastic-like layer below the lithosphere is called called asthenosphere.asthenosphere. The rigid plates of the The rigid plates of the lithosphere float and move around on the lithosphere float and move around on the asthenosphere.asthenosphere.

Causes of Plate TectonicsCauses of Plate Tectonics Convection currents cause the movements of platesConvection currents cause the movements of plates Hot, less dense liquid or gas is forced upward, as it Hot, less dense liquid or gas is forced upward, as it

reaches the surface, it cools down and sinks back reaches the surface, it cools down and sinks back down. This entire cycle of heating, rising, cooling down. This entire cycle of heating, rising, cooling and sinking is called a and sinking is called a convection currentconvection current..

No plate can budge without affecting the other plates surrounding it!

Plate BoundariesPlate Boundaries When plates move, they can interact in several When plates move, they can interact in several

ways. Three different moving types of plates are:ways. Three different moving types of plates are: Plates moving apart (Divergent)Plates moving apart (Divergent) Plates moving together (Convergent)Plates moving together (Convergent) Plates slide past each other (Transform)Plates slide past each other (Transform)

Faults break in Earth’s crust Faults break in Earth’s crust where rocks have slipped past each where rocks have slipped past each other.other.

Plate boundaries are where the Plate boundaries are where the edges of different pieces of the edges of different pieces of the lithosphere meet.lithosphere meet.

Gummy TimeGummy Time

Boundary ActivityBoundary Activity

Transform BoundaryTransform Boundary

Two plates slip past each other, moving in Two plates slip past each other, moving in opposite directions. opposite directions. (Do not push or pull)(Do not push or pull)

Crust is neither created nor destroyed near a Crust is neither created nor destroyed near a transform boundary.transform boundary.

Earthquakes occur frequently along these Earthquakes occur frequently along these boundaries.boundaries.

Divergent BoundaryDivergent Boundary

Two plates Two plates move apartmove apart or diverge. or diverge. Most occur at the mid-ocean ridge; they can also Most occur at the mid-ocean ridge; they can also

occur on land (occur on land (poor Africa).poor Africa). A rift valley is a deep valley that forms along the A rift valley is a deep valley that forms along the

divergent valley.divergent valley. The Great Rift Valley in Africa marks a deep crack in

the African continent that runs for about 3,000 km. When divergent boundaries develop on land, two of When divergent boundaries develop on land, two of

Earth’s plates pull apart.Earth’s plates pull apart.

Convergent BoundaryConvergent Boundary

Two plates come together or collide (converge)Two plates come together or collide (converge) Results: earthquakes, trenches, volcanoes, Results: earthquakes, trenches, volcanoes,

mountainsmountains When two plates collide the denser of the two When two plates collide the denser of the two

plates will sink or slide beneath the other.plates will sink or slide beneath the other.

3 types of convergent boundary 3 types of convergent boundary outcomesoutcomes

1)1) Oceanic crust meets continental crust:Oceanic crust meets continental crust:

Oceanic crust meets oceanic crust:Oceanic crust meets oceanic crust:

Continental crust meets continental crust:Continental crust meets continental crust:

Example: Folded MountainsExample: Folded Mountains

The continents’ slow danceThe continents’ slow dance

The plates move at slow rates about 1 to 10 cm The plates move at slow rates about 1 to 10 cm per year.per year.

http://youtu.be/hSdlQ8x7cuk

To prevent confusionTo prevent confusion Not all volcanoes Not all volcanoes

occur at plate occur at plate boundaries. For boundaries. For example, the example, the Hawaiian islands Hawaiian islands formed from a formed from a hot spot volcano. As the . As the Pacific plate moves Pacific plate moves across a fixed hot spot across a fixed hot spot (mantle plume), new (mantle plume), new volcanoes (and volcanoes (and islands) form.islands) form.

SummarySummaryTheories: Continental Drift

Theory Theory of Plate

Tectonics

Forces of PlateMovement:

Cycle of Convection Currents

Ridge Push/Gravity Slab Pull******

Types of Plate Movement/Interactions: (Boundary)

Divergent Convergent Transform

Processes or Types of Movement (Results):

Sea-floor Spreading

Subduction (Volcanoes) andMountains

Earthquakes

Stress: Tension Compression Shearing

Faults: Normal Reverse Strike Slip

Cookie TimeCookie Time

Boundary ActivityBoundary Activity