Chapter 17 Section 2, chapter 17, Science chapter 17, Chapter 17 Plate Tectonics Section 4 sea-floor Spreading

49. Spreading rates along mid-ocean ridges have ________.

changed through time, and today vary between 1 and 10 cm/yr

sea-floor spreading

the process by which molten material adds new oceanic crust to the ocean floor

what are the steps of seafloor spreading and how many are there

5 steps 1.magma pushes into ocean ridge 2.new crust is made 3. Ocean ridge continues to spread as new magma reaches earths surface 4. plate moves outward from the ridge 5.crust is destroyed when the plate sub ducts and forms a trench

deep-ocean trenche

A deep valley along the ocean floor beneath which oceanic crust slowly sinks toward the mantle.

Which continent is now part of Eurasia but, according to theory, was originally a separate continent that moved northward into its present position?

Continents have distorted by earthquakes, volcanoes and climate changes a little over time, and the coast has eroded over time.

16. Limestone reefs and salt deposits are important rocks in the reconstruction of Earth history because they ________.

can be used to infer the ancient climate of the Earth; they are deposited in environments that are restricted to warm climate

29. Which of these parts of the deep-ocean floor is flat and nearly featureless?

abyssal plain

Harry Hess, an American geologist was one of the scientists who studied mid-ocean ridges.

after examining maps of mid-ocean ridge system he had a startling conclusion...Maybe wegener was right! Perhaps the continents do move.

3. Currently, most geologists ________.

agree that continental drift occurs due to mechanisms at work in the ocean basins and upper mantle

30. Seafloor spreading is driven by volcanic activity ________.

along mid-ocean ridges

33. Within the sea floor, the rate of geothermal heat flow is greatest ________.

along mid-ocean ridges

What happens to the rock along the ridge when new molten material erupts?

The older rock moves outward on both sides of the ridge as new rock forms in the center of the ridge from cooling of molten material. This process is sea floor spreading.

Subduction

The process by which oceanic crust sinks beneath a deep-ocean trench and back into the mantle at a convergent plate boundary.

Subduction and Earth's oceans

The process of subduction and sea-floor spreading can change the size and shape of the oceans. Because of these processes, the ocean floor is renewed about every 200 million years. That is the time it takes for new rock to form at the mid- ocean ridge, move atoss the ocean, and sink into a trench.

Why does the rock of the ocean floor have a pattern of magnetic stripes?

The rock of the ocean floor contains iron. As molten material cooled and hardenend, the iron bits inside lined up in the direction of Earth's magnetic poles, creating a pattern of magnetized stripes.

Wegener proposed continental drift after he observed evidence from fossils, glacial deposits, and the fit of the continents that suggested all of the continents were once ________.

combined to form a supercontinent he termed Pangaea

7. Wegener saw Pangaea as a jigsaw puzzle, where the puzzle pieces were ________.

continents

2. What is NOT the result of plate tectonics?

convection in the outer core

Name 4 effects that are found at a divergent boundary between oceanic plates?

creation of new seafloor; widening ocean basin; volcanic activity; fissures make mid-ocean ridges

20. The apparent polar-wander path obtained from magnetite crystals in basalts on the North American continent is now interpreted to be primarily the result of ________.

drifting of the North American continent

Surprisingly, the geological features of the strange environment on the ocean floor provide some of the best evidence

for Wegener's hypothesis of contintal drift.

42. Regions of the sea floor with positive magnetic anomalies were formed during times when Earth's magnetic field ________.

had normal polarity

43. Regions of the sea floor with negative magnetic anomalies were formed during times when Earth's magnetic field ________.

had reversed polarity

40. All basalts younger than 700,000 years old ________.

have normal magnetic polarity

Wegener's idea of continental drift was rejected by American geologists because ________.

he could not conceive of a valid mechanism that would cause continents to shift positions

18. In the geologic past, the polarity of the Earth's magnetic field is ________.

known to have experienced numerous reversals, as shown by remnant magnetization of iron-rich minerals in rocks

4. Wegener's evidence for a united Pangaea comes from the fossil record of which type of organisms?

land animals

10. In Wegener's evidence for continental drift, continents were proposed to fit together, such as the east coast of South America with the ________.

lower west coast of Africa

25. If you were using both a compass and a map marked with latitude and longitude to navigate, you might note the angle difference between your compass and what is marked on the map, called ________.

magnetic declination

26. What does an ordinary compass indicate?

magnetic north

46. Marine magnetic anomalies result from seafloor spreading in conjunction with ________.

magnetic polarity reversals

28. Where Earth's magnetic dipole intersects with the surface of the planet is called the ________.

magnetic pole

21. Which mineral is integral to paleomagnestim?

magnetite

6. Evidence that the South American and African continents were once joined includes evidence from their coastlines such as ________.

matching fossil distributions

45. Marine magnetic anomaly belts run parallel to ________.

mid-ocean ridges

36. A great boost in seafloor exploration and a greater understanding of seafloor bathymetry was a result of ________.

military needs in World War II

Sea- Floor Spreading

molten material erupts throught the valley that runs along the center of some mid-ocean ridges. This material hardens to form the rock of the ocean floor.

Each cycle of spreading and magma intrusion along an ocean ridge results in the formation of this

new ocean crust

32. The map below depicts earthquakes, which primarily coincide with areas where ________.

volcanoes also regularly occur

Magma hardens to form new ocean crust is what step out of three.

3

Magma is forced upward toward the crust is step what out of three.

1

what are the 4 steps of seafloor spreading

1. the seafloor spreads apart along both sides of a mid-ocean ridge. 2. A new crust is added. 3. belts, carrying the continents along with them

Magma fills the gap that is created is step out of three

2

35. The oldest basalts on the ocean floor are about ________ years old.

200 million

For the best arrangement, which continent forms the core of Pangaea?

Africa

Which two continents have the best fit?

Africa & South America

What happens as subduction occurs?

As subduction occurs, crust closer to a mid-ocean ridge moves away from the ridge and toward a deep-ocean trench. Sea-floor spreading and subduction work together. They move the ocean floor as if it were on a giant conveyor belt.

New ocenaic crust is hot. But as it moves away from the mid-ocean ridge, it cools and becomes more dense. Eventually, gravity pulls this older, denser oceanice crust down beneath the trench.

As the sinking crust floating on the water gets wet, its density increases and begins to sink.

What happens to oceanic crust at a deep-ocean trench?

At a deep-ocean trench, the oceanic crust bends downward. In a process taking tens of millions of years, part of the ocean floor sinks back into the mantle at deep-ocean trenches.

17. Distinctive rock sequences on South America terminate at the Atlantic Ocean but reappear on the continent of ________.

Australia

Name 2 examples of a divergent plate boundary?

East Africa Rift Valley & Ethiopia Rift

The oldest ocean floor rocks are about 3.8 billion years old. True or False

False; 180 million

An isochron is a change in Earth's magnetic field. True or False

False; Magnetic reversal

Deep-sea trenches are vast, underwater mountain chains. True or False

False; Mid-ocean ridges

The magnetic patterns on either side of a deep-sea trench are mirror images of each other. True or False

False; Ocean ridge

The theory of continental drift states that new ocean crust is formed at ocean ridges and destroyed at deep-sea trenches. True or False

False; Sea floor spreading

As new seafloor is carried away from an ocean ridge, it heats up, expands, and becomes less dense than the material beneath it. True or False

False; cools, contracts, and becomes more dense

The thickness of ocean-floor sediments decreases with distance from an ocean ridge. True or False

False; increases

Rock samples taken near ocean ridges are older than rock samples taken near deep-sea trenches. True or False

False; younger

Magnetic Stripes

Figure 17....____________________ in the rock of the ocean floor show the direction of Earth's magnetic field at the time the rock hardened.

around these hot-water vents in the ocean floor the most bizarre creatures live

Giant, red tipped tube worms, giant clams and strange spider like crabs.

What scientist helped to discover the processs of sea-floor spreading?

Harry Hess

What is unusual about Iceland?

Iceland is a portion of the mid-atlantic ridge that rose above sea level. it has frequent volcanic activity

What happens at deep-ocean trenches?

In a process taking tens of millions of years, part of the ocean floor sinks back into the mantle at deep-ocean trenches.

Wht occurs at trenches?

In a process taking tens of millions of years, part of the ocean floor sinks back into the mantle at deep-ocean trenches.

In 1960 Hess suggested that a process called sea-floor spreading contiually adds new material to the ocean floor.

In sea-floor spreading, the sea floor spreads apart along both sides of a mid-ocean ridge as new crst is added. As a result, the ocean floors move like conveyor belts, carrying the continents along with them.

What is the process of sea-floor spreading?

In sea-floor spreading, the sea floor spreads apart along both sides of a mid-ocean ridge as new crust is added. As a result, the ocean floors move like conveyor belts, carrying the continents along with them.

Why is the Atlantic Ocean expanding?

In the Pacific Ocean, subduction through the many trenches that ring the ocean is occurring faster than new crust can be added. Unlike the Pacific Ocean, the Atlantic Ocean is expanding. It has only a few short trenches. As a result, the spreading ocean floor has nowhere to go. As the Atlantic's ocean floor spreads, the continents along its edges also move and the ocean gets wider.

Earth's -------- ------ has changed over time. A field with the same orientation as today's field is said to have ------ -----------. Magnetometers have been used to generate --------- maps, which have shown that the ocean floor is ------- near ocean ridges and ----- near deep-sea trenches.

Magnetic field, normal polarity, reversed polarity, isochron, younger, older

Device that can detect small changes in magnetic fields

Magnetometer

Along what feature of the ocean floor does sea-floor spreading begin?

Mid-Ocean ridge

Where would you expect to find the oldest rock on the ocean floor?

Nearer to deep ocean trenches

8. Late Paleozoic glacial deposits are NOT found in what continent?

North America

37. Deep-ocean trenches are found predominantly along the perimeter of the ________ .

Pacific Ocean

What is the evidence for sea-floor spreading?

Several types of evidence supported Hess's theory of sea-floor spreading: eruptions of molten material, magnetic stripes in the rock of the ocean floor, and the ages of the rocks themselves.

The Deep-Ocean Floor

Shrimp, crabs, and other organisms cluster near hot water vents in the ocean floor.

Why is the Pacific Ocean shrinking?

Sometimes a deep-ocean trench swallows more oceanic crust then a mid-ocean ridge can produce. Then, if the ridge does not add new crust fast enough, the width of the ocean will shrink. In the pacific ocean, subduction through the many trenches that ring the ocean occur-ing faster then the new crust can be added.

What device is used to map the ocean floor?

Sonar

How are these matching stripes evidnece of sea-floor spreading? (figure 17 pg. 144)

Stripes of rock formed when Earth's magnetic field pointed north alternate with stripes of rock that formed when the magnetic field pointed south. The alternating pattern is the same on both sides of a mid-ocean ridge.

Sea-Floor Drilling

The Glomar Challenger was the first research ship designed to drill samples of rock from the deep ocean floor.

The mid-ocean ridge system is more than 50,000 kilometers long.

They extend into all of Earth's oceans. Most of the mountains in the mid-ocean ridge system lie hidden under hundreds of meters of water. But in a few place the ridge pokes above the surface. ex Iceland is a part of the mid-ocean ridge that rises above the surface in the North Atlantic Ocean. A steep-sided valley splits the top of some mid-ocean ridges.

24. According to the figure below, Earth's magnetic poles move constantly. About how far from the geographic poles do the magnetic poles move?

They remain in the high latitudes.

Earthquake activity and volcanism are common along ocean ridges. True or False

True

Maps made from sonar and magnetometer data led to the discovery of ocean ridges and deep-sea trenches. True or False

True

Sonar uses sound waves to measure water depth. True or False

True

The study of the magnetic record preserved in Earth's rocks is called paleomagnetism. True or False

True

The theory of seafloor spreading explains that Earth's continents move because they ride atop ocean crust as it moves away from ocean ridges. True or False

True

1. Wegener's proposal that the continents had once fit together as a single supercontinent was rejected by geologists at the time because ________.

Wegener could not provide a driving force

How does new oceanic crust form?

When molten material erupts through the mid ocean ridge called sea-floor spreading

Deep in the ocean, the temperature is near freezing.There is no light, and living things are generally scarce.

Yet some areas of the deep-ocean floor are teeming with life. One of these areas is the East Pacific Rise. This area forms part of the Pacific Ocean floor off the coasts of Mexico and South America. Here Ocean water sinks through cracks, or vents in the crust. The water is heated by contact with hot material from the mantle. The hot water then spurts back into the ocean.

What is a deep-ocean trench?

a deep valley along the ocean floor where oceanic crust slowly sinks toward the mantle; a convergent boundary

sonar

a device that bounces sound waves off underwater objects and then records the echoes of these sound waves. The time it takes for the echo to arrive, indicates the distance to the object.

Sea-Floor Spreading begins at a mid-ocean ridge, which forms along a crack in the oceanic crust.

along the ridge, molten material that forms several kilometers beneath the surface rises and erupts. at the same time, older rock moves outward on both sides of the ridge. As the molten material cools, it forms a strip of solid rock in the center of the ridge. When more molten material flows into the crack it forms a new strip of rock.

Mid-ocean ridges

an undersea mountain chain where new ocean floor is produced.

What Is a striation? Why are they there?

are scratches or gouges cut into bedrock by glacial abrasion(the movement of the glacial). They are there because there is gravel stuck under the glacier so as it moves they apear.

39. The thickness of clay and planktonic microskeletons is greatest ________.

at the edges of ocean basins

38. Beneath a blanket of sediments, oceanic crust is primarily composed of ________.

basalt

23. Evidence of paleomagnetism can be found in ________.

basalt that has cooled from lava, any rock with magnetic minerals present, sedimentary rocks, where minerals form from ion-bearing groundwater (All of the above are correct).

Several types of evidence supported Hess's theory of sea floor spreading:

erruptions of molten material, magnetic strips in the rock of the ocean floor, and the ages of the rocks themselves.

What three types of evidence provided support for the theory of sea floor spreading?

eruptions of molten material, magnetic stripes in the rock of the ocean floor, and the ages of the rocks themselves.

34. With increasing distance from a mid-ocean ridge, the age of oceanic crust ________.

increases

Because of sea-floor spreading, the distance between Europe and Noth America

is increasing by a few centimeters per year.

13. If we mentally align the continents to fit Wegener's concept of Pangaea, evidence of Late Paleozoic glacial deposits ________.

is much more readily explained than in the modern continental configuration

The Pacific Ocean covers almost

one third of the plantet.

The discovery that each continent had different and separate polar-wander paths such as those in the figure below proved that ________.

only the continents move

41. According to the figure below, marine magnetic anomalies lay roughly ________ to mid-ocean ridges.

perpendicular

19. The apparent tendency of the north (or south) magnetic pole to vary in position over time is termed ________.

polar wander

44. Consult the figure below. Marine magnetic anomaly belts are widest when and where ________.

seafloor spreading rates are relatively rapid

31. Volcanoes that have submerged beneath the surface of the sea are termed ________.

seamounts

47. Earth's magnetic reversals are likely due to ________.

tectonic plates shifting

12. If a geologist discovered coal in a modern-day cold, snowy location, he or she could conclude that ________.

the area was once covered with swamps and/or jungles

what is seafloor spreading

the formation of new areas of oceanic crust, which occurs through the upwelling of magma at midocean ridges and its subsequent outward movement on either side.

What is till?

the mixture of sediments that a glacier deposits directly on the surface

How can the ocean floor keep getting wider and wider?

the ocean floor generally does not just keep spreading. Instead, the ocean floor plunges into deep underwater canyons called deep-ocean trenches. At a deep-ocean trench, the oceanic crust bends downward.

Mantle

the part of the Earth that makes up two-thirds of its mass and flows like silly putty

Inner Core

the part of the earth that has the highest pressure and hottest temperature

Lithosphere

the part of the earth that is made of the crust and the uppermost part of the mantle

Crust

the part of the earth that is the least dense and the thinnest layer

Outer Core

the part of the earth that stops or slows down seismic waves because it is made of liquid metal

Asthenosphere

the part of the earth that the plates move on and acts like plastic

48. By deep-sea drilling, the Glomar Challenger proved the theory that if the model of seafloor spreading was correct, then seafloor sediment should be ________ and ________ as one moves away from the spreading axis.

thicker and older

11. Evidence that glaciers once covered an area might include ________.

till and striations

Where would the densest oceanic crust be found?

under the deep ocean trenches. New oceanic crust is hot. As it moves away from the mid-ocean ridge toward a deep ocean trench it cools and becomes more dense.

if you had a hot cup of water that was in a squared figure and you poured cold water dyed blue what would you see happening

you could see the blue (cold water) sink to the bottom toward the left side and goes around the edges of the square till it completes a full circle.