Chapter 11

Pgs 11-4 to 11-29

Layers of the Earthpgs 11-4 to 11-6 The current theory is

that the Earth’s interior consists of multiple layers: Inner core Outer core Mantle Crust

The inner core

The center of the Earth Made up primarily of iron,

nickel, other heavy elements

It is theorized to be solid due to enormous pressure

The Outer Core

Made of the same elements as the inner core, but with less pressure, it is theorized to be liquid

The Mantle

Contains mostly silicon and oxygen

makes up nearly 80 percent of the Earth's total volume.

Consists of the upper and lower mantle

The upper mantle itself is made of 2 layers Asthenosphere Lithosphere

Lithosphere and Asthenosphere Lithosphere

includes the uppermost, rigid part of the upper mantle and the crust.

Asthenosphere Solid but flows slowly over time Hotter, less dense material

(magma) rises towards the surface where it can eventually flow from a volcano or other opening. At this point the molten rock is lava.

The flowing asthenosphere carries the lithosphere of the Earth, including the continents, on its back.

The Crust

composed mainly of oxygen, silicon, magnesium, and iron

Varies in thickness and is the outer layer of the lithosphere

11-7 to 11-8 Isostatic Equilibrium

Even before the plate tectonics theory emerged, scientists believed that the crust floated on the denser mantle below Still believed today

Continental crust (crust under the continents) Ocean crust (crust under the ocean basins)

Oceanic crust is thinner and denser than continental crust Because the continental crust is made of

granite and the oceanic crust is made of basalt rock

Interaction of Oceanic Crust and Continental Crust With the crust resting on the mantle, there

must be a balance between the weight of the crust and the upward force of buoyancy called isostatic equilibrium

As material adds to the oceanic crust from sedimentation, glaciers and volcanic activity or from the continental crust from erosion, this balance becomes disrupted. This is one theorized cause of earthquakes. To restore equilibrium, landmasses will sink or

rise slightly along a weak area called a fault.

The accepted theory of plate tectonicssuggests that the continents move inhorizontal directions and that earthquakesalso result from that movement.

The Theory of Continental Drift11-10 to 11-13 Proposed by Alfred Wegener All earth’s continents had been a single

continent that he called Pangaea

CONTINENTAL DRIFTPangaea broke up with part of the continent drifting north and part south. 1) The northern part split to form the North Atlantic Ocean 208-146 million years ago (mya). 2) The South Atlantic and Indian oceans began to form 146-65 mya. 3) The continents continue to drift. Today the oceans are still changing shape; the Atlantic Ocean gets wider by a few inches each year.

Surrounding Pangaea was a single large ocean he called Panthalassa

The theory that all of the continents were once a single landmass that drifted apart (and are still doing so) is called the theory of continental drift

Evidence for Continental Driftpgs 11-10 through 11-13

Appeared that the continents fit together like jigsaw puzzle pieces

Fossils found in different locations Distribution of coal Glacial rock deposits Limestone deposits Salt deposits

Criticism of Continental Drift

Wegener was a meteorologist, not a geologist Could not give an explanation of how the

continents could drift Jigsaw puzzle had gaps

Seafloor Spreading pgs 11-14 to 11-18

New technology- sonar Came about at the same time as the continental

drift theory and partly in response to the Titanic disaster

The German Meteor mapped the contours and depths of the South Atlantic in 1925 using sonar

The ability to map the seafloor in greater detail revealed important new features: Mid-ocean ridges are enormous mountain

ridges on the bottom of the ocean. Rift valleys are deep valleys

running through the center ofmid-ocean ridges such asthe Atlantic Ridge.

Trenches are deep ravinesin the seafloor.

The idea that the seafloor is in a constant state of creation and destruction is called seafloor spreading- an explanation proposed by Harry Hess and Robert Dietz.

New crust emerges from the rift valley in a mid-ocean ridge

Magma from the asthenosphere pushes up through the rift and solidifies into new crust

As more magma pushes up from below, it pushes new crust away on each side of the ridge

New seafloor near the ridge continuously pushes old seafloor away from the ridge

Evidence for Seafloor Spreading11-17 to 11-18

Ocean-bottom sediment samples Glomar Challenger- coring

Radiometric dating Used to determine the

age of rocks Seafloor rock-

significantly younger than rock in the center of the continents (theory states that seafloor rock subsides and continental rock doesn’t).

Magnetometer data measures the polar

orientation and intensity of magnetism of minerals

Scientists towed magnetometers around the seafloor beginning in 1950

discovered that the seafloor on either side of the mid-ocean ridges roughly mirrors each other’s polar orientation

Divergent, Convergent, & Transform Plate Boundaries 11-22 to 11-25

The theory of plate tectonics unites the theories of continental drift and seafloor spreading. Earth’s lithosphere consists of more than a

dozen separate plates rigid and float on the asthenosphere.

Divergent Boundaries

At a spreading, or divergent boundary, two plates are moving apart

The crust pulls apart and forms valleys. Magma flows up through the rift valleys creating new crust

and widening the seafloor. Mid-ocean ridges and rift valleys mark divergent

boundaries.

Hot Spots Stationary plume of

magma under a moving plate

Creates volcanic islands in the middle of plates

EX: Hawaiian Islands and the Emperor Seamount Chain

Convergent Boundaries At a colliding or convergent boundary, two

plates push together also called destructive boundaries because

movements along these destroy crust Subduction zones (convergent boundary).

A trench forms as a more dense oceanic plate moves under a less dense continental plate. As subduction occurs, some of the material from the melting oceanic plate rises upward to form volcanoes on the continent.

Mountain formation at continental plate collision.

Transform Boundaries

At a transform boundary or fault, two plates slide past each other. Earthquakes result as rocks move when the

plates slide next to each other. Ex: California’s San Andreas Fault

Ocean Floor Topography Vocabulary Continental Shelf: the part of the continent that

is under water. It is the biologically richest part of the ocean. At times of low sea level the shelves were exposed.

Continental Slope: the edge of the continent. Extends downward to the deep-sea floor.

Continental Rise: a gentle slope or a rise on the bottom of the ocean that is due to the sediments being carried down the slope. The sediment is carried downward by the turbidity current.

Seamount: underwater volcanoes due to hotspots and magma. Formed when magma below is pushed upward and cooled and solidified.

Mid-Ocean Ridge: the cracks in the bottom of the ocean where the plates meet. Is called an underwater mountain range.

Rift Valley: a valley between 2 plates. Caused when the 2 plates are pushed apart and the sea-bottom collapses forming a valley between the 2 ridges.

Abyssal Plain: the almost perfectly flat area of the ocean. Flat due to deposits of sediments and erosion. Called the ocean desert because few life forms exist here.

Guyot: a flat-topped underwater mountain. It is flat at the top due to erosion.

Trench: a narrow depression on the sea floor. Caused when 2 plates collide and one plate is pushed under the other one and pulls the sea bottom with it. The deepest trench is the Marianas trench with a depth of 11,022 meters, or almost 7 miles.

SONAR: uses echolocation or sound waves to see the seafloor and make an accurate map of it.

SONAR is used to make accurate maps of the ocean floor.

Sediments: 12-10 to 12-12 Lithogenous sediments come from the land

Mainly result from erosion by water, wind, and ice carrying rock and mineral particles into the sea.

Other lithogenous sediments enter the sea from landslides and volcanic eruptions

Make up majority of sediments found near continents and islands

Includes sand and clay

Biogenous sediments: originate from organisms Particles in the sediment come from shells and

hard skeletons Cover the largest area of sea floor. The majority of biogenous sediment comes from

planktonic organisms that obtain siliceous and calcareous compounds from seawater.

Under the right conditions, organic molecules in the sediment form crude oil (petroleum) and natural gas

Hydrogenous sediment results from chemical reactions within seawater Less than 1% of the seafloor sediments Form slowly

Cosmogenous sediments come from outer space Made up of small particles the size of sand or

smaller called cosmic dust. Some thought to result from collisions between

objects in space Meteors: large, fast-moving objects that enter the

atmosphere Meteorite: a meteor that strikes the ground

Least abundant of the sediments- a few parts per million of marine sediment per year