Ch 10

Ch 10 Tetonic plates- miss kelleyBell ringer 11/18Two islands are 1,000 km apart. The rocks on both islands are said to have the same mineral compositions. Simillarly fossils found on both islands contain the same rare specifies of plants. The mountain range on both islands also are identical in age (found through carbon decay) and structure. Explain a hypothesis that suggests why both islands are so similar.

Werner's hypothesis Continental drift- all the continents were once a supercontinent. They started breaking about 200 million years ago (mesozoic era). Over millions of years these contients drifted into where they are currently held today. Suggested that the deformation of the plates may account for land structures such as mountain ranges. Like pieces of a puzzleCan you identify pieces that fit together like a puzzle?Tear your continents out similarly to the ripping of tectonic plates.Arrange your continents together to form s puzzle of your purposed super continents. Present your super contient

Evidence- fossilsWegener reasoned that if the continents were fused togther similar plant and animal fossils would be found on 2 or more different continents. Mesosaurus- found on both South America and Western Africa

Evidence- fossils

270 million years agoNo land bridgesNot likely that this small reptile swam across the Atlantic ocean Evidence- rocksRocks across different continents were also found to be similar Type Structure Age ( carbon dating)

Examples- Appalachians in USA and mountains in GreenlandScotland and northern EuropeWestern ranges in Africa and Southern South America.

Rock type

Evidence- rocksGreenland Appalachians

Evidence-climatemountainsfossilsScientist discovered debris of glaciers in South America and AfricaTropical fossilised plants in both areas support the idea that South America and Western Africa were once joinded. Evidence-climate changeWegener's Theory FossilsSupports the idea that climates were very different because continents were in much different locations

Example- Antarctica was not always a barren frozen wasteland. It once had a tropical warm climate

Evidence-not adding upWhy do you think his evidence wasnt supported by the scientific community at that time ( 1912 Germany) Purposed that continents drifted and ripped across ocean floors, and plowed through huge rock formations. Evidence-mid ocean rangesmid-ocean ridges- undersea mountain ranges which create steep narrow valleysScientists noticed specific trends about these ridges in 1947

Sediment that covers the ocean floor is thinner next to the ridgeThe closer the sediment was to the ridge the younger that materials were

Ocean floor is very youngMountains on land 3.8 million yearsOcean mountains 180 million yearsDebris closer to the ridge is much younger than further away

Mid Atlantic Ridge

mid ocean ridge

Ridges on the earth

Bell ringer 11/19How many continents exist of the earths surface? How many tectonic plates does each one have?Sea floor spreadingHess- suggested that the valleys in the midle of ocean ridges is a crack or riftMagma rises to fill this crackAs it rises it cools to form new igneous rockThis replaces the ocean floor

Dietz- names this sea-floor spreading- process which new oceanic lithosphere forms as magma rises to earths surface this solidifies at a mid-ocean ridgeSuggested if the sea floor was spreading so would the contients

paleomagnetismAs magma solidifies iron minerals align with the earths magnetic fields this becomes permanent as the rock hardens. Magnetic reversal- scientists discovered rocks whos manetism is in the wrong directionsouth polarity) fell into group of certain time periodsNoticed patterns when comparing reversed and normally magnetised rocks Geomagnetic reversal time scale-

Magnetic symmetryScientists noticed stripped magnetic patterns on the ocean floorAlternating bands of reversed polarityMatches the geomagnetic time scale

Scientists could then assign ages to the rocks that compose the sea floorYoungest rocks at the center while the older are on the outsideNew rock forms at the center of the ridge then spreads out in opposite direction..supporting Hesss idea of sea-floor spreading

Reading checkHow are magnetic patterns in sea-floor rock evidence of sea-floor spreading?On landRocks on land also showed similar characteristic s of reverse magnetismMatches the reversal magnetism found below the ocean

Scientists reasoned that sea-floor spreading can explain why continents can move over the earths surface.Section 2- theory of plate tetonicsPlate tetonics- theory that explains why and how the continents move and the formation of the features of the earths crust

Tectonics- derived from the Greek word tektonikos- constructionTetonic plates3d puzzle piece- take shape of contient but then show depth or height

Lithosphere- upper part of the mantle, thin outer shell of the earthBROKEN INTO TETONIC PLATES

Tectonic plates

asthenosphere- plastic rock below the lithosphere

Solid rock that flows like putty

Oceanic crust-dense rock rich in Fe and MgContinental crust- low density made up of rock rich in silica (Si)15 major tectonic plates- bordering mts or deep sea ranges

Bell ringer 11/19 Math practiceTectonic plates move slowly on the Earths surface. In 2 million years, how far would a plate travel if it moves for 4 cm per year. Fun fact about tectonic platesThe world's greatest land mountain range is the Himalaya-Karakoram. It contains 96 of the world's 109 peaks of over 7317 meters (24,000 feet). The longest mountain range is the Andes of South America which is 7564 km (4700 miles) in length. Both were created by the movement of tectonic plates. How was Hawaii formed ?http://www.history.com/shows/ how-the-earth-was-made/videos/how-was-hawaii-formed

Tectonic platesScientist study the major shift which cause

Earthquakes- sudden movements along the boundaries of tectonic plates and the plate shifts.

Volcanoes= can form when plates shift causing an exposure of magma Example- pacific ring of fire- active volcanoes around the pacific ring which also causes earth quakesThis zone is surrounded by plate boundaries.

https://www.youtube.com/watch?v=ryrXAGY1dmE Types of plate boundaries3 main types- can be on land through the continent, surrounding the continent, or on the ocean floor,

Divergent- plates move away from each otherConvergent- plates push into neighboring boundaries and collideTransform boundaries plate edges slide past one another.

Divergent Earth's brittle surface layer (the lithosphere) is pulled apart, it typically breaks along parallel faults that tilt slightly outward from each other. As the plates separate along the boundary, the block between the faults cracks and drops down into the soft, plastic interior (the asthenosphere). The sinking of the block forms a central valley called a rift. Magma (liquid rock) seeps upward to fill the cracks. In this way, new crust is formed along the boundary. Earthquakes occur along the faults, and volcanoes form where the magma reaches the surface.

Mid- Atlantic riftImage: A diver swims between the Eurasian and North American plates in Thingvellir lake, Thingvellir National Park, Iceland. Iceland is one place where a mid-ocean ridge can be seen on land and in shallow waters.(credit: Wild Wonders of Europe/Lundgre)convergentPlates pull apart at one boundary and push into another neighboring plate. Convergent boundaries- point where two plates collide (3 types)1st typeOceanic lithosphere collides with continental lithosphere

Andes Mountains

Why does that happenThe oceans lithosphere is less dense than the continental lithosphereIt Subducts or sinksRegion where one plate moves under another- subduction zone As this occurs fluids cause the mantle to melt forming magma which rises to the surface to form volcanic mountains

2nd type

2 plates of contiental lithosphere collideNeither plate is dense enough to subductEdges crumble and thicken and uplift to form large mountains

Bell ringer 11/21What might the united States be like if we were centered over the equator

What might the US be like of it were centered over the North Pole?

3rd typeCollision between 2 oceanic lithosphere platesOne plate subducts underneath the other Fulids released causes mantle rock to melt and form magma Magma rises to the surface of the ocean to form an island arc or chain of islands

Transform boundariesTwo plates slide past each otherMid ocean ridges are connected by transform boundaries- fracture zonesNot smoothlySpurts of motion- earthquakesSt. Andreas Fault in CaliforniaMid-ocean ridge connected to transform boundaries= fracture zones

What causes plate motion?MANTLE CONVECTIONenergy generated by earths core heat mantle materialheated material rises (LESS DENSE)Cold material sinks (MORE DENSE)Mantle drags the overlaying plates with it

This explains the movement RIDGE PUSHnewly formed rock at a mid-ocean ridge is warm(LESS DENSE) rises up above rockAs it cools it sinks (MORE DENSE)Asthenosphere exerts a Force ridge push up

Reading checkHow might density differences in the rock at the mid ocean ridge drive plate motion?Section 3- reshaping the earths crust Stable rock- cratons- ancient cores around which todays continents were formed The exposed part of this rock= shields

Rifts- In simple terms, a rift can be thought of as a fracture in the earth's surface that widens over time, or more technically, as an elongate basin bounded by opposed steeply dipping normal faults. continents are broken apart

Heat may build up beneath the mantle causing the continental lithosphere to become thinnerEventually a rift forms and the continent can break apart

terranes

Piece of lithosphere with unique and different history than surrounding lithospheresDifferent rock/fossils Major faults/boundariesMagnetic properties arent the same

Continents can grow by accumulating crustal material along their edges at convergent boundaries. Here, a terrane carried by a subducting plate is fused to the edge of a continent. The attachment of terranes such as this contributed to continental growth along the west coast of North America.