Plate tectonics, sea floor spreading and continental drift, structure of the earth(Unit #4)

how are earths layers separated by

composition and physical properties (temperature, density, and pressure).

what do scientists use to identify earths layers?

seismic waves

The Crust properties

Solid, brittle

Thinnest Layer

how much of the earths mass does the crust provide

1%

how thick is the crust

5-100 km

two types of crust

continental and oceanic

was does the continental crust include

• all continents and major islands

what is the continental crust made of

• silica-rich minerals (granite).

how old are the 2 crusts

c- more than 4 billion o-less than 180 million

earths thickest layer

mantle

what layer makes up 67% of earths mass?

mantle

what is the mantle mainly made of

iron and magnesium

what matter is the mantle made of

top is cool but below is hot and sot(plastic like)

where are earths convection currents and what do they do

• n the mantle bring hot material from the lower mantle up where it is cooled to then sink back down.

whats the core made of

• Mostly iron but has nickel in it too.

makes up 33% of earths mass

the core

matter in the outer core…

liquid

matter in the inner core

solid

what does the lithosphere include

earths crust and upper mantle

what is the Asthenosphere

• Plastic-like layer of the mantle below the lithosphere.

who proposed continental drift and in what year

by Alfred Wegener in 1912

what were the evidence for continental drift

Fossil Clues, Climate Clues, Rock Clues,

fossil clues

Fossils of fresh-water reptile (Mesosaurus) found in different continents, now separated by an ocean.

Climate Clues

• Fossils (Glossoteris) was found in too large an area to have lived in one type of climate.

Rock Clues

• Rock structures from different continents are similar.

why wasn’t wegners’s idea automatically accepted

because they had no reason on why the continents were moving Wegener could not explain what forces could be large enough to cause the continents to move.

who proposed the idea of sea floor spreading

by Harry Hess

sea floor spreading

• a theory by Harry Hess that explains how new oceanic crust is formed at ocean ridges, then moves away from the ridge

what was used to measure water depths and map the ocean floor

sonar

what did scientists discover on the sea floor that was very important

1. underwater mountain ranges called ocean ridges, and 

2. long narrow depressions in the seafloor called deep-sea trenches

what discover about sea floor spreading was made by using samples of deep sea sediment

• The ages of ocean crust and the thicknesses of ocean-floor sediments increase with distance from the ridge.

what is earths magnetic field generated by

the flow of molten iron in the outer core.the flow of molten iron in the outer core.

whats the polarity of the earth flipping called

magnetic reversals.

what shows proof of magnetic reversals

Ocean rock is mostly basalt, which contains a lot of iron.  The basaltic rocks on the ocean floor

So when these normal and reverse polarities are shown on a map the result is

a series of strips across the floor parallel to the ridge and the ages and widths of the strips match on both sides of the ridge.

what was the missing link wegner needed to prove continental drift?

sea floor spreading

seafloor spreading not only proves that the continents are moving but also….

the sea floor

Plate Tectonics is a theory based on…..

both Continental Drift and Seafloor Spreading.

what does the theory of plate tectonics describe?

It describes how tectonic plates move and shape Earth’s surface. 

what are the three types of plate boundaries?

Divergent, convergent, transform

what happens at divergent boundaries?

plates move away from each other.

what happens at convergent boundries?

• plates are coming together’

what happens at transform boundaries

• plates are sliding past each other.

what drive plate movement

Convection currents in the mantle

what causes the convection currents in the mantle

Temperature differences inside the Earth’s mantle causes the hot, plastic-like rock to be forced up toward the surface.

he cycle of heating, rising, cooling, and sinking is called

convection

where do plates diverge

where hotter liquid rises.

where do plates converge

where cooler liquid sinks.

how much do tectonic plates move a year

1 cm

what features do divergent boundaries cause

• Mid-Ocean Ridges

• Rift Valleys

ex of features of Div. boundaries

• Mid-Atlantic Ridge

• East African Rift

features of transform boundaries

• strike-slip faults

earthquakes.

ex of features of Trans. boundaries

• San Andreas Fault

features of convergent boundaries.

• Volcanic Mountains

• Deep Sea Trenches

ex features of con. subduction

Volcanic Mountains Deep Sea Trenches

what happens at convergent subduction boundaries

plates move together

ex of features of a convergent subduction boundary (oceanic-continental)

• Andes Mountains

• Cascade Range

features of a convergent subduction boundary (continental-continental)

• Island Arcs

• Deep Sea Trenches

ex of features of a convergent subduction boundary(oceanic oceanic)

• Islands of Japan

• Aleutian Island

features of convergent collision boundaries

Folded and fault-block mountains

ex of features of convergent collision boundaries

• Himalayan Mts.

• Appalachian Mts.