THE EARTHInterior

Crust layer of rock that forms Earth’s skin includes dry land and ocean floor most places 5- 40 km thick in a few places, under mountains,

can be as thick as 70 km similar to skin of onion

Mantle made of hot rock, but solid nearly 3000km thick three regions: Lithosphere

upper part similar to crust- rigid 100km

Asthenosphere hotter and ↑ pressure like soft tar

Lower Mantle Hotter, but still solid

   

Core made mostly of iron and nickel

two parts:liquid outer coresolid inner core

heat has melted metals in outer core pressure in inner core is so great molecules

cannot spread out to the liquid formation this results in the metals being forced into

the solid state recent evidence has shown inner core may

contain O, S, Si

Earth’s Magnetic Fieldbelieve that movement of liquid outer core creates magnetic field

remember that Earth acts like a giant bar magnet

the field around the magnet is the magnetosphere

Convection

is the flow that transfers heat within a fluid

heating and cooling of the fluid, changes in the fluid’s density, and the force of gravity combine to set convection currents in motion

these currents continue as long as heat is added

Convection

Convection in Earth

in Earth’s mantle large amounts of heat are transferred by convection currents

heat from the core and the mantle itself causes currents

this rising and sinking happens over thousands/ millions of years

there may also be currents in the outer core

this plus the nickel and iron cause the magnet in the Earth

• in 1910 a German scientist, Wegener hypothesized that all the continents were once joined together in a single landmass and have since drifted apart•this idea that the continents/ crust moves is called CONTINENTAL DRIFT•the one continent has been called Pangaea•he gathered evidence from different areas to support his idea

Continental Drift

-All continents one land mass surrounded by ocean

Pangaea

Evidence for Continental Drift

He could see the evidence, but could not explain the way the earth’s crust moved.

evidence is from:land featuresfossilsclimate change

Land Features rocks and formations of rocks support the

evidence of continental drift the theory of Pangaea rock formations in

Africa (west) line up with one in South America (east)

Brazil has coal fields with identical layers found in Africa

Glacial erosion also exists in SA, Africa, India, and Australia that match similar patterns

Fossils similar fossils have been found in SA and

Africa Glossopteris is an extinct fern This fossil found in rocks approx 250 my old

and is found in Africa, India, and Antarctica seeds from these plants were too large to

be dispersed by wind from one continent to the other

the seeds could only be dispersed in smaller areas like joined lands

 

Climate Change salt, coal, and limestone support evidence that

continents had very different climates long ago it is not due to climate change, but rather change in

position of the lands today most salt deposits range from 10-30ْ

latitude rock salt has been found in MI coal is only formed in warm swampy climates today coal deposits have been found in Antarctica limestone from coral reefs found in Texas and

central US 

Wegener’s theory of Continental Drift was rejected at the time

Other geologist acknowledged the evidence

But they did not know or understand how the continents could move (no known mechanism)

LithosphereA portion of the earth that includes the crust and the upper part of the mantle that acts as one unit in its motion

Can be different in its composition and softness

Earth’s Layers

Earth’s Upper Layers

MOVEMENT OF THE CRUST

Observation meets theory!

Mid-Ocean Ridges cracks or vents found on the Earth’s

crust of the ocean floor (oceanic crust) these areas rise above the surrounding

crust underwater mountains, but most are

under hundreds of meters below surface a few are above the water (island of

Iceland, islands in the Philippines) underwater volcanoes discovered through sonar

Sea Floor Spreading in 1960 Hess, an American geologist, proposed the sea floor spreads apart along both sides of a mid-ocean ridge as new crust is added

the ocean floor is like a conveyor belt, carrying the continents along with them

New crust being made

Mid-Ocean Ridge

Trenches if this theory is true the mid-ocean ridges

produces new crust through volcanic eruptions and the floor spreads slowly

at some point the floor (conveyor belt) must return

at ocean trenches the crust undergoes SUBDUCTION

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

new oceanic crust is hot coming out of ridge, but it cools as it moves away and then sinks

this takes ten of million of years

because of this process the ocean floor is renewed every 200M years

the Pacific Ocean is shrinking

the Atlantic Ocean is growing

see figure

Evidence for Ocean Floor Spreading

Molten MaterialMagnetic StripesDrilling Samples

Molten Materialin 1960 a very small specialized sub, ALVIN, examined some ridges

it found rocks shaped like pillows

such rocks only form when material hardens quickly after erupting under water

Magnetic Stripes earth is like a gigantic magnet oddly at times the poles reverse

themselves last time 780,000 years ago the rocks in the oceanic crust made

up of iron hold this record of the magnetic field as it comes out of ridge

using sensitive instruments scientist can record the magnetic memory of the rocks

the ocean floor shows stripes of these fields

Drilling Samples Glummer Challenger, a drilling

ship, sent drilling pipes through the water 6Km deep

samples from sea floor were aged

farther away from a ridge the samples were older

youngest around a ridge

Sea Floor Spreading

Subduction

Subduction

Trench

PLATE TECTONICS

Putting it all together

The Theory

in 1965 a Canadian scientist, Wilson, discovered there are cracks in the continents similar to those on the ocean floor

he saw the lithosphere was broken into pieces he called PLATES (both oceanic and continental plates)

Wilson combined the knowledge of plates, sea-floor spreading, and continental drift to come up with one unifying theory

Plate Tectonics

the theory of PLATE TECTONICS explains the formation, movement, and subduction of Earth’s plates

pieces of Earth’s lithosphere are in slow constant motion driven by the convection currents of the mantle

during subduction gravity pulls one edge of a plate down into the mantle

the rest of the plate also moves as the plates move, collide, pull apart, or grind

past each other amazing changes occur in Earth’s surface

Earth’s Plates

Plate Boundaries

the edges of plates meet at plate boundaries, deep in lithosphere

FAULTS occur at these points Faults are breaks in the Earth’s

crust where rocks have slipped past each other (major points of earthquakes)

Plate Boundaries

there are three types of boundaries:

DivergentConvergentTransform

Divergent

the point where two plates move apart

most occur along mid-ocean ridges where sea-floor spreading occurs

some do happen on landon land, a huge rift valley formse.g. Great Rift Valley in Africa

Convergent

place where plates come together, collisions this results in a collision the density of plates will determine what will

happen oceanic crust becomes cooler and denser as

it spreads away from the mid-ocean ridge Pressure of water also condenses oceanic

crust In general oceanic plates (OP) more dense

than continental plates (CP)

When 2 OP plates converge the denser sinks under the other less dense plate

When OP and a CP collide, the OP is more dense than CP and will slide under the CP

when 2 CP collide they are too close in densities for subduction

instead the plates collide and squeeze the crust into huge mountain ranges

Transform

a place where two plates slip past each other

no subduction occurs no crust is created or destroyed high earthquake activity at these points all this moving of the plates containing

ocean and continents have shaped the surface of the Earth since its formation