World Oceans Chapter 2

The Earth's atmosphere is composed of:

- Mostly made of: nitrogen N2 gas = 70% oxygen - Small amounts of argon, methane, carbon dioxide, dust, ozone, and water vapor

The Earth's Interior densities and where they go:

1) The densest material sank to the center to form the core. 2) The least dense materials rose to the surface to form the crust. 3) Gases vented to form the oceans and atmosphere.

Two kinds of crust:

1) continental crust 2) oceanic crust

Three Types of Convergent Boundaries:

1) oceanic-oceanic 2)oceanic-continental 3) continental-continental

Antonio Snider

1858, publishes maps showing continental drift

seismograph

A device that records ground movements caused by seismic waves as they move through Earth

Who proposed the theory of Continental Drift in 1915?

Alfred Wegener

The Earth's hydrosphere includes:

All the water on earth

Refraction in waves

Bending of wave path as it encounters layers of different seismic velocity

reflection in waves

Bounce off layers of different velocity and density

Isostasy

Buoyant support of lithosphere by asthenosphere

Lithosphere

Crust and upper mantle fused together -rigid & brittle

At the outer core of the Moho

Decrease in P-wave velocity and no S-wave transmission through liquid

Asthenosphere

Deformable region in the mantle (partially melted,1%) -Low velocity zone (seismic)

Earth model 2:

Earth has layers having different strengths and physical properties -Developed with the theory of plate tectonics

Earth model 1:

Earth has layers of different mineral and chemical composition -Original method used

Earth's interior: ______ waves reveal Earth's structure

Earthquake waves reveal earth's structure Arrival times of seismic waves -Generated by earthquakes, volcanic eruption, human-made explosions -Speed depends on chemistry, density and physical state (solid, partially molten, molten)

The Isostasy principle is also illustrated by ______ .

Icebergs Why: The proportion of a large iceberg below water can be 3-9 times greater than the proportion above the water's surface.

At the inner core of the Moho

Increase in P-wave velocity

If Earth's crust is Solid rock, and the Mantle is softer, why doesn't the crust sink into the mantle?

Isostasy

Evidence for Seafloor spreading: JOIDES Resolution

J: joint O: oceanographic I: institutions D: deep E: earth S: sampling

Layers within the mantle

Lithosphere, Asthenosphere, and Mesosphere

The base of the crust is _____

Moho

Two types of polarity

Normal polarity and Reverse polarity

Two types of body waves:

P (primary) waves and S (secondary) waves

If an object is floating in the water, equal pressure must be maintained on all parts of the ocean floor.

Part of the object will be submerged and part of it will protrude above the surface. The higher the object protrudes (i.e. the larger or thicker the object), the deeper its base projects into the water.

Harry Hess

Proposed the theory of sea-floor spreading, known as Mantle Convection

What does seismology teach us about Earth's interior?

Reflection seismology used to estimate the depth of sediment layers and underground reservoirs

Evidence for sea floor spreading: heat flow

Researchers sank probes into the ocean crust to measure heat flow patterns near mid ocean ridges

Evidence for seafloor spreading: sediment age & thickness

Sediment is thicker and older with increasing distance from the ridges

The average rate of spreading is about 1 cm per year on each flank of the ridge.

Spreading rates range 1 - 10 cm/yr

Wilson Cycle

The cyclical opening and closing of ocean basins caused by movement of the Earth's plates.

Convection

The transfer of heat by the movement of a fluid *driven by heat in the mantle *It is believed that thermal convection in the asthenosphere drags lithospheric plates and causes molten (less dense) rocks to rise.

Because of isostasy, the earth's crust floating on top of the molten mantle behaves differently depending on its constitution:

Thin, dense oceanic basalt rests at a depth of 3800 meters below sea level. Thick, less dense continental granite crust rests at 840 meters above sea level.

Ridge-push, slab pull

Two forces that contribute to driving plate motions •Elevated ridges create sloping seafloor •Old seafloor is cold, thick, dense

Subduction zones:

a broad band of strong earthquakes signifies intense deformation (compression) of the crust in these areas: • along the western edges of North and South America • across the western and northwestern Pacific • across Asia to the Himalayas • into Europe and the Alps

The mechanism causing lithospheric plates to move is thought to be

a combination of convection in the mantle and "slab pull" caused by subducting lithosphere.

Two types of seismic waves

body waves and surface waves

The Earth's biosphere includes all organic matter, living or non-living. It consists mostly of:

carbon, hydrogen, and oxygen

The speed of seismic waves depend on:

chemistry, density and physical state (solid, partially molten, molten)

The two Earth models are ________ not _______

complimentary not contradictory

The growth of the basin causes the continents on either side to move further apart:

continental drift.

What drives continental drift?

convection currents in the mantle

The _____, about 3500 km thick, is the innermost layer. -It includes a molten outer core and a solid inner core -Both are composed of very dense alloys of iron and nickel.

core

The _____ is the thinnest (ranging from about 3-65 km) and least dense of the layers. -It is rich in silicon, aluminum, and oxygen.

crust

Earth is formed of concentric layers:

crust, mantle, liquid outer core, and solid inner core

When Earth cooled from its initial molten state, its components separated out according to their:

densities

Three types of plate boundaries

divergent, convergent, transform

When plates converge at a subduction zone, one slab plunges below the other, causing:

earthquakes as its surface scrapes along the rocks above it. *When the descending slab reaches a depth of 100-200 meters, it melts and is spewed up as andesite lava in volcanic island arcs.

Seismic waves are generated by:

earthquakes, volcanic eruption, man-made explosions

The Earth's Exterior ________

envelopes

New ocean floor and crust are continuously created by:

extrusion of basalt at the crest of mid ocean ridges, leading to seafloor spreading.

paleontological evidence

fossil evidence

Atmosphere : ______ surrounding the solid Earth

gases

Seafloor spreading:

is the mechanism behind the movement of the continents.

Crust and mantle can be divided into:

lithosphere, asthenosphere, and mesosphere

Biosphere: ______ organisms and _____ compounds

living, organic

The ______, about 2900 km thick, comprises dense, relatively hot rocks. -It is rich in magnesium, iron, silicon, and oxygen.

mantle

The oceans' oldest sediments are found

on top of the basalt layer, far from spreading centers.

The geomagnetic field points out of the Earths' surface at the ____ Pole, and into the surface at the _____ Pole.

out at the south into the north

Alfred Wegener used geological and ____________ evidence to suggest that the Earth's continents were one large landmass more than 200 million years ago.

paleontological evidence

According to Alfred Wegener, The giant landmass, ____, broke apart along a global system of geologic faults and moved away into their current locations over millions of years.

pangea

Lithosphere is Broken into _____

plates

The Earth's magnetic force changes _____ from time to time, which is recorded in the geologic record.

polarity

The intensity of Earth's magnetic field is strongest at the _____

poles

Mesosphere (lower asthenosphere)

pressure increases and raises the melting point -Entirely solid

P-waves

primary waves travel faster than any other -Compression waves - slinky-like motion -Travel through solid, liquid, and gas

P waves travel through mantle and _______ in and out of outer core

refract

If seafloor is expanding in some areas, but the size of the Earth remains the same, that means:

seafloor must be destroyed elsewhere.

S-waves

secondary waves travel slower. They are the second waves to arrive at the station. -Shear waves - perpendicular motion -Only travel through solids

A fixed volcanic hot spot on Earth tends to produce a _______ on a moving plate.

series of volcanic peaks

Magnetic stripes on the seafloor are created at

spreading centers.

Francis Bacon (~1600)- observed:

the "fit" of continents

Seafloor spreading at the Mid-Atlantic ridge is currently causing symmetrical expansion of:

the Atlantic basin.

The inclined plane of earthquakes is called:

the Benioff zone.

Isostasy depends upon the principle that:

the pressure exerted by water on the ocean floor is proportional to the height and density of the water, and to the strength of gravity.

The process of spreading ocean ridges can be visualized using:

the stripes of magnetic anomalies laid down when the new rocks were formed.

Continental crust

thick low density granite rocks; chemically heterogeneous

Oceanic Crust

thin high density basalt rocks; chemically homogeneous

Plates move horizontally past each other along

transform faults.

t/f It is believed that thermal convection in the asthenosphere drags lithospheric plates and causes molten (less dense) rocks to rise.

true

t/f S waves travel through mantle but not outer core

true

t/f The deepest earthquakes occur in subduction zones at oceanic-oceanic plate convergent boundaries.

true

t/f The driving mechanism behind plate movement is still under investigation.

true

Identify all of the different observations used to support Harry Hess' theory of seafloor spreading.

• Seafloor magnetic anomalies. • Dipping zones of earthquakes at ocean trenches. • Shallow earthquakes along transform faults. • High heat flow at oceanic ridges.

Rates of Motion

• Variable between 1-20 cm/yr (10-200 mm/yr) • Generally between 2-10 cm/yr (20-100 mm/yr)

Evidence for crustal motion

•Distribution of earthquake epicenters •heat flow •sediment age, and thickness •Paleomagnetism

Wegener's Evidence

•Fit of the continents •Ancient mountain belts •Patterns of glaciation •marine fossils in high mountain settings, •deep ocean trenches next to island arcs •Volcanic islands bordering coastlines

Heat flow facts from seafloor spreading:

•High heat flow near ocean ridges, where crust is thinnest and closes to the rising heat from the mantle •crust is colder and older with increasing distance from the ridge

divergent boundaries

•Mantle upwelling •Layers of oceanic crust *creation of ocean basins

Convergent boundary

•Plates collide •Often subduction

Evidence of Seafloor spreading: Rock Magnetism

•Researchers also found stripes of alternating negative and positive magnetism on the flanks of ridges. •They run parallel and are symmetrically arranged on both sides of the midocean ridge axis.

Paleomagnetism

•Reversal of magnetic poles •Nearly 170 reversals have been identified during the last 76 million years •Present orientation has lasted 780,000 years • magnetic stripes

When lava cools, the magnetic minerals (magnetite) in it align themselves with the geomagnetic field as they crystallize.

•Rocks "record" the strength and direction of the magnetic field at the time that the rocks were formed •This is called paleomagnetization.

While most volcanic activity occurs at plate boundaries, mantle plumes can melt up through the lithosphere. This causes:

•This causes lava to pour out on top of the plate. •The motion of the plate over the mantle plume (or "hotspot") can cause island chains, like the Hawaiian Islands.

Transform boundary

•Usually offset segments of ocean ridges (two divergent boundaries) •Can also join up different combination of divergent and convergent boundaries * faults and Fracture zones

Wegner's theory was wrong about what is causing continental drift:

•Wegner surmised that continents "plow" their way through ocean crust •Wegner attributed the driving force of the motion to Centrifugal force from Earth's rotation

Evidence for sea floor spreading

•drilling sediment cores establishes the age and thickness of sediment resting on top of the crust •Sediment is thicker and older with increasing distance from the ridges

The discovery of the Mid-Atlantic ridge (during WWII) revealed mysteries that led to the discovery of seafloor spreading, such as:

•the presence of young basalt in the rift valley •extremely high temperatures in the zone of spreading •frequent earthquakes and volcanic activity