Plates Shape Continents - Middle School Earth and Space Science

Which coastline fit is the classic example used to support continental drift?

South America and Africa. Their eastern and western coastlines fit remarkably well when joined.
What seafloor feature is a long underwater mountain chain where new ocean crust forms?

Mid-ocean ridge. Magma rises here, creating new oceanic crust that pushes plates apart.
What seafloor feature most directly marks where one oceanic plate sinks beneath another plate?

Ocean trench. The deepest point where subduction occurs.
What is the main limitation of using only continental shapes as evidence for plate motion?

Coastlines change; continental shelves fit better than shorelines. Erosion alters coastlines; shelves preserve original edges.
What is the term for the sinking of one tectonic plate beneath another at a trench?

Subduction. Denser oceanic plate sinks beneath less dense plate.
Identify the best seafloor evidence that plates move sideways past each other along a boundary.

Transform faults offsetting ridge segments. These faults show lateral plate motion without subduction.
What is the name of the process where a denser plate sinks beneath another plate at a trench?

Subduction. Occurs when oceanic crust is recycled back into the mantle at trenches.
Identify the seafloor evidence that oceanic crust is youngest at ridges and older farther away.

Seafloor age pattern (age increases away from the ridge). New crust forms at ridges and moves outward over time.
Identify the seafloor feature that offsets segments of mid-ocean ridges and indicates horizontal motion.

Transform fault. Fractures where ridge segments shift horizontally.
Which seafloor location has the oldest oceanic crust: near a ridge or far from the ridge?

Far from the mid-ocean ridge. Older crust has moved away from its formation point over time.
Which seafloor evidence shows that oceanic crust is youngest at mid-ocean ridges and older farther away?

Age pattern of seafloor rocks (young at ridge, older outward). New crust forms at ridges and moves outward over time.
Identify the seafloor feature: a long, elevated underwater mountain chain at a divergent boundary.

Mid-ocean ridge. Forms at divergent boundaries where plates separate.
Identify the plate-boundary type most consistent with a trench and a chain of volcanic islands nearby.

Convergent boundary with subduction. Volcanic arcs form above descending oceanic plates.
Which seafloor feature is a deep, narrow depression marking a subduction zone?

Ocean trench. Deepest parts of ocean where one plate descends beneath another.
Choose the correct conclusion: Basalt near a ridge is younger than basalt far from the ridge. What does this indicate?

New crust forms at ridges and moves outward (seafloor spreading). Age progression proves crust forms at ridge and spreads.
Identify the boundary type if a map shows a deep trench parallel to a volcanic island arc.

Convergent boundary with subduction. Trenches and volcanic arcs are classic subduction features.
Which observation best supports that old oceanic crust is recycled back into the mantle?

the oldest seafloor is near trenches and none is extremely old. No seafloor exceeds 200 million years old due to subduction recycling.
Which seafloor feature best indicates the location of frequent shallow earthquakes at a spreading center?

Mid-ocean ridge. Shallow quakes occur where plates pull apart and magma rises.
Which pattern of seafloor rock ages supports seafloor spreading at mid-ocean ridges?

Youngest at ridge; ages increase with distance from ridge. New crust forms at ridge center and moves outward over time.
What is the main reason oceanic crust is typically younger than continental crust?

It is continuously created and recycled by plate tectonics. Old oceanic crust subducts while new crust forms at ridges.
What seafloor process occurs at mid-ocean ridges that creates new oceanic crust?

Seafloor spreading. Magma rises and solidifies, pushing plates apart.
What seafloor feature forms a long underwater mountain chain where new oceanic crust is created?

Mid-ocean ridge. New seafloor forms here as plates pull apart.
What magnetic pattern in seafloor basalt supports seafloor spreading?

Symmetrical magnetic stripes on both sides of ridges. Earth's magnetic reversals recorded in cooling basalt create patterns.
What pattern of seafloor age across a mid-ocean ridge supports seafloor spreading?

Youngest at the ridge, older farther away. New crust forms at the ridge, so age increases with distance from it.
Which option best indicates a divergent boundary on the seafloor: ridge or trench?

Ridge. Ridges mark where plates separate and new crust forms.
Identify the boundary type if a map shows a trench parallel to a volcanic island arc.

Convergent boundary with subduction. Trenches and volcanic arcs form where oceanic plates subduct.
What type of evidence uses the "jigsaw fit" of continental coastlines to support plate motion?

Continental fit (matching continental shapes). Continents fit together like puzzle pieces, suggesting they were once connected.
What is the term for a linear chain of volcanoes formed as a plate moves over a hot spot?

Hot spot track (volcanic island chain). Plate motion over stationary magma source creates age progression.
What is the term for one tectonic plate sinking beneath another at a convergent boundary?

subduction. Occurs at convergent boundaries where oceanic crust is recycled.
Which seafloor feature is a deep, narrow depression commonly found at convergent boundaries?

Deep-ocean trench. Forms where one oceanic plate descends beneath another.
Which type of plate boundary is indicated by a deep-ocean trench on the seafloor?

convergent boundary. Plates collide here, with one descending into the mantle.
Which statement best matches seafloor evidence: 'Crust gets older away from a ridge'?

Plates diverge and seafloor spreads outward from the ridge. Age pattern proves new crust forms at ridge and spreads outward.
Identify the relationship between seafloor age and distance from a mid-ocean ridge.

Seafloor age increases with distance from the ridge. Proves new crust forms at ridges and moves outward.
Which part of a hot spot volcanic chain is usually the oldest if the hot spot is stationary?

The volcano farthest from the active hot spot. Plate has moved farthest from the magma source over time.
What seafloor feature is a long underwater mountain chain where new ocean crust forms?

mid-ocean ridge. Forms at divergent boundaries where plates separate and magma rises.
What plate-boundary type is indicated by a deep-ocean trench and subduction?

Convergent plate boundary. Plates collide, causing one to subduct into the mantle at trenches.
What is the name of the deep, narrow seafloor feature commonly found where plates converge?

Ocean trench. Forms where one plate subducts beneath another.
Which seafloor feature most directly marks where plates separate in the middle of an ocean basin?

Mid-ocean ridge. Divergent boundary where oceanic plates spread apart.
What is a rift valley, and where is it commonly found relative to a mid-ocean ridge?

A valley at the ridge crest where crust is pulling apart. Forms where plates separate at spreading centers.
What seafloor pattern shows symmetric, parallel bands on both sides of a mid-ocean ridge?

Magnetic striping (magnetic reversals recorded in basalt). Earth's magnetic field reversals are preserved in cooling basalt.
Identify the correct conclusion: If magnetic stripes are mirror images across a ridge, what occurred?

New crust formed at the ridge and spread outward. Symmetry proves crust formed at ridge and moved outward equally.
Which seafloor feature is the long underwater mountain chain that marks many divergent plate boundaries?

Mid-ocean ridge. Forms where plates pull apart and magma rises.
Which specific continent pair is the classic example of matching coastlines supporting plate motion?

South America and Africa. Their coastlines match remarkably well when fitted together.
Which observation about South America and Africa supports past connection of continents?

Their coastlines fit together like puzzle pieces. The matching shapes suggest they were once connected before drifting apart.
Identify the best evidence type: continental shape match or mid-ocean magnetic stripes for plate motion?

Mid-ocean magnetic stripes. Magnetic stripes provide quantitative, measurable plate motion evidence.
Which continental fit is the classic example used as evidence for plate motion?

South America and Africa. Their coastlines match remarkably well when brought together.
Which conclusion is supported if basalt near a ridge is younger than basalt far from the ridge?

New oceanic crust forms at the ridge and moves outward. Age progression proves seafloor spreading from the ridge.
Identify the plate motion conclusion if ocean-floor basalt is youngest at the ridge and older on both sides.

plates are moving away from the ridge (diverging). Age pattern proves new crust forms at ridge and spreads outward.
Which seafloor feature most directly marks the location where new crust is created?

The crest of a mid-ocean ridge. The ridge axis is where magma erupts to form new oceanic crust.
What is the name of the supercontinent inferred from matching continents and seafloor evidence?

Pangaea. All continents joined ~250 million years ago before breaking apart.
Which statement best links seafloor features to plate motion: ridges create crust or destroy crust?

Ridges create new crust; trenches destroy (subduct) old crust. Plate tectonics recycles crust through creation and destruction.
Identify the best evidence from seafloor maps that a plate is being subducted.

A trench with a line of deepening earthquakes landward of it. Descending plate creates trench and deep earthquake pattern.
Which conclusion is supported if magnetic stripes on both sides of a ridge are mirror images?

Seafloor is spreading outward from the ridge on both sides. Mirror patterns prove new crust forms at the ridge center.
Identify the plate boundary type found at a mid-ocean ridge where plates move apart.

Divergent plate boundary. Plates separate here as new crust forms from rising magma.
What is the best evidence from the seafloor that plates have moved over long periods of time?

Seafloor age and magnetic stripes that record spreading away from ridges. Dating and magnetic patterns prove continuous plate movement.
Which option best indicates a convergent boundary on the seafloor: ridge or trench?

Trench. Trenches form where plates collide and one subducts.
What does the close fit of continental coastlines suggest about Earth's past plates?

Continents were once joined and later moved apart. Matching coastlines indicate past connection before plate separation.
Which type of plate boundary is indicated by a mid-ocean ridge on the seafloor?

divergent boundary. Plates move apart here, creating new oceanic crust through volcanism.
What term names the ancient supercontinent formed when most landmasses were joined?

Pangaea. Greek for 'all Earth,' it existed about 250 million years ago.
What is the seafloor feature called where a ridge is offset in a step-like pattern?

Transform fault (fracture zone). Horizontal sliding motion offsets ridge segments without creating/destroying crust.
Choose the correct inference if two continents fit like puzzle pieces across an ocean basin.

they were once connected and later separated by plate motion. Matching coastlines suggest continents split apart by seafloor spreading.
Which boundary type best matches the seafloor feature: a deep-ocean trench?

Convergent boundary (subduction zone). Trenches form where oceanic plates descend into the mantle.
Which option best indicates plate motion away from a ridge: youngest rocks far away or at the ridge?

Youngest rocks are at the ridge. New crust forms at ridges, so rocks get older with distance.
What does it mean if matching magnetic stripes occur on both sides of a mid-ocean ridge?

Crust formed at the ridge and moved outward equally on both sides. Symmetric spreading creates matching patterns on both sides.
What is the name of the idea that continents were once joined and later moved apart?

Continental drift. Wegener's hypothesis that continents move across Earth's surface.
Identify the correct conclusion if ocean-floor rocks are youngest at the ridge crest.

New crust forms at the ridge and moves outward. Young rocks at ridge prove new crust forms there and spreads laterally.
Identify the seafloor feature that is typically higher in elevation: mid-ocean ridge or deep-ocean trench?

Mid-ocean ridge. Ridges are elevated; trenches are the deepest ocean features.
Which boundary type is indicated by an ocean trench: divergent, convergent, or transform?

Convergent boundary. Plates collide and one descends beneath the other.
Identify the plate-motion direction if magnetic stripes mirror across a ridge axis.

Plates move away from the ridge in opposite directions. Mirror symmetry proves equal spreading in both directions from ridge.
Which seafloor feature offsets segments of mid-ocean ridges and indicates sideways motion?

Transform fault. Fracture zones where plates slide past each other horizontally.
What is the term for the idea that continents were once joined and later moved apart?

continental drift. Wegener's theory proposed continents moved across Earth's surface over time.
Which continental margin shape match is classic evidence that South America and Africa were once joined?

the east coast of South America fits the west coast of Africa. These coastlines fit together like puzzle pieces when reconstructed.
What is the relationship between ocean-crust age and distance from a mid-ocean ridge?

Ocean crust gets older with increasing distance from the ridge. New crust forms at ridge; older crust pushed farther away.
Which plate boundary type is most strongly indicated by an ocean trench and subduction?

Convergent plate boundary. Plates collide, with one sinking at the trench.
Which hot spot chain is commonly used to infer Pacific Plate motion direction over time?

Hawaiian–Emperor seamount chain. Shows Pacific Plate moved northwest then changed direction 43 million years ago.
What is the process called when new oceanic crust forms at mid-ocean ridges and moves outward?

Seafloor spreading. Magma rises at ridges, cools into new crust, and pushes older crust outward.
Which seafloor feature most directly marks the location where oceanic crust is destroyed?

A deep-ocean trench. Old oceanic crust descends into the mantle at these locations.
Identify the seafloor feature: a long, narrow, very deep depression where one plate sinks.

Deep-ocean trench. Deepest parts of ocean where subduction destroys old crust.
What is the term for the large, rigid pieces of lithosphere that move and carry continents?

Tectonic plates. Earth's outer shell divided into moving sections carrying continents.
What seafloor feature is the main location where seafloor spreading occurs?

Mid-ocean ridge. Underwater mountain chain where new oceanic crust forms.
What seafloor process at mid-ocean ridges creates new oceanic crust?

Seafloor spreading. Magma rises and solidifies as plates pull apart at ridges.
Identify the seafloor pattern that shows crust gets older with distance from a ridge.

Rock ages increase away from the mid-ocean ridge. Youngest rocks at ridge, oldest near continents or trenches.
Which direction does oceanic crust move relative to a mid-ocean ridge during seafloor spreading?

Away from the ridge on both sides. Seafloor spreading pushes crust outward from the ridge center.
Which type of evidence uses the way continental coastlines match to support past connection?

Continental shape (jigsaw-fit) evidence. Coastlines fit together like puzzle pieces when reassembled.
Which continental pair is the classic example of matching coastlines used as plate-motion evidence?

South America and Africa. Their coastlines fit together like puzzle pieces when reconstructed.
What seafloor pattern shows alternating bands of normal and reversed magnetism parallel to mid-ocean ridges?

magnetic striping. Records Earth's magnetic field reversals preserved in cooling basalt.
Which seafloor feature provides the strongest evidence that oceanic crust is recycled back into the mantle?

Deep-ocean trench (subduction zone). Old oceanic crust descends into the mantle at trenches.
Which seafloor feature is a deep, narrow depression formed where one plate subducts beneath another?

Deep-ocean trench. Forms where denser oceanic plate sinks beneath another.
What is the main limitation of using only coastline shapes as evidence for plate motion?

Coastlines change due to erosion and sea level. Coastlines constantly change, making them unreliable markers.
Which seafloor feature would you expect at a divergent boundary in the middle of an ocean basin?

A mid-ocean ridge. Divergent boundaries create ridges where plates separate.
Which boundary is most consistent with new crust forming and plates moving apart?

Divergent plate boundary. Plates separate and new crust forms at divergent boundaries.
Choose the best evidence for plate motion found on the seafloor rather than on continents.

Magnetic striping and seafloor age patterns. These patterns directly record seafloor spreading processes.
Which seafloor feature best indicates the location of deep earthquakes along a subduction zone?

Deep-ocean trench. Deep quakes occur as subducting plate descends into the mantle.
What magnetic pattern on the seafloor provides evidence that new crust forms and moves away from ridges?

Symmetrical magnetic stripes (magnetic reversal pattern). Earth's magnetic field reversals are recorded in cooling lava.
Which boundary is most consistent with old crust being destroyed and a trench forming?

Convergent boundary with subduction. Old oceanic crust sinks and melts at convergent boundaries.
What is the term for a line of volcanoes that forms as a plate moves over a mantle hot spot?

hot spot track. Stationary magma source creates volcanic chain as plate moves over it.
Which two modern continents are most commonly cited as fitting together like a puzzle?

South America and Africa. Their eastern and western coasts match like puzzle pieces when brought together.
What seafloor feature commonly offsets segments of mid-ocean ridges with sideways motion?

Transform fault (fracture zone). Plates slide past each other horizontally at these zones.
Which plate boundary type is indicated by transform faults that cut across and offset ridges?

Transform plate boundary. Plates slide sideways past each other without creating or destroying crust.
What plate-boundary type is indicated by a mid-ocean ridge with seafloor spreading?

Divergent plate boundary. Plates move apart at ridges, creating new oceanic crust between them.
What seafloor feature forms where new oceanic crust is created as plates move apart?

Mid-ocean ridge. Underwater mountain chain where magma rises and solidifies.
Which direction do seafloor magnetic stripes run relative to a mid-ocean ridge?

Parallel to the ridge. Stripes form as new crust records magnetic field during spreading.
Identify the seafloor feature if a map shows a long ridge down the center of an ocean basin.

Mid-ocean ridge. These underwater mountain chains mark divergent plate boundaries.
If basalt is youngest at the ridge and older away from it, what process does this support?

Seafloor spreading. Age pattern proves new crust continuously forms at ridges.
What magnetic pattern in ocean crust on both sides of a ridge supports seafloor spreading?

Symmetrical magnetic stripes parallel to the ridge. Earth's magnetic reversals create matching patterns as crust spreads.
Which observation about continental coastlines supports past connection of continents?

Matching shapes of continental margins (jigsaw fit). Coastlines fit together like puzzle pieces when reassembled.
Choose the correct statement: If seafloor rocks are youngest at a ridge, what does that show?

Seafloor spreading is creating new oceanic crust. Young rocks at ridges prove active crust formation there.
Which seafloor location has the youngest oceanic crust: near a ridge or near a trench?

Near a mid-ocean ridge. New crust forms continuously at spreading centers.
Which seafloor feature should you identify if earthquakes form a deepening zone beneath an island arc?

a subduction zone at a deep-ocean trench. Earthquake depth increases as subducting plate descends into mantle.
Which seafloor observation best indicates the direction of plate motion away from a ridge?

Crust ages increase with distance from the ridge. Older crust farther from ridge proves outward movement.
Which part of a continent is most accurate to compare when testing the "puzzle-piece" fit?

The edges of the continental shelves. Continental shelves mark true continental boundaries.
Which statement best links continental shapes and seafloor features as evidence of plate motion?

Continents fit together and seafloor spreads from ridges over time. Both show plates have moved from past positions.
What evidence from the seafloor directly supports the idea that plates move apart at ridges?

Symmetric magnetic stripes and increasing crust age away from ridges. Mirror patterns prove new crust forms at ridge and moves outward equally.
What seafloor pattern shows symmetrical bands on both sides of a mid-ocean ridge?

Magnetic striping (symmetrical polarity bands). Earth's magnetic field reversals are recorded in cooling seafloor rocks.
Which seafloor topography change is expected when moving away from a mid-ocean ridge?

Ocean depth increases as the crust cools and sinks. Older, cooler crust contracts and subsides with distance.
What seafloor feature marks a divergent boundary where new oceanic crust forms?

Mid-ocean ridge. Underwater mountain chain where plates separate and magma rises.
Identify the best modern match for continental fit if using the continental shelf edges, not coastlines.

South America and Africa match more closely along shelf edges. Continental shelves preserve original break-up edges better than modern coasts.
What is Pangaea?

A past supercontinent that included most landmasses. Broke apart ~200 million years ago into today's continents.
Which statement is supported if two continents have matching coastlines but are now separated by an ocean?

The continents were once joined and later moved apart. Continental drift separated once-connected landmasses.
Which seafloor feature is a deep, narrow valley where old oceanic crust sinks into the mantle?

Deep-ocean trench. Forms where oceanic plates bend downward and sink into the mantle.
What process at mid-ocean ridges provides seafloor evidence that plates move apart?

Seafloor spreading. New crust forms at ridges, pushing older crust outward.
Which boundary type is indicated by a mid-ocean ridge: divergent, convergent, or transform?

Divergent boundary. Plates separate and new crust forms between them.
Which boundary type best matches the seafloor feature: a transform fault offsetting ridges?

Transform boundary. Plates slide past each other along these fracture zones.
What pattern of magnetic polarity on the seafloor supports seafloor spreading?

Symmetrical magnetic stripes on both sides of ridges. Mirror-image patterns prove new crust forms at the ridge center.
What is the relationship between earthquake locations and plate boundaries on the seafloor?

Earthquakes cluster along plate boundaries. Most earthquakes occur where plates interact and move.
Which observation best supports seafloor spreading: magnetic stripes are the same on both ridge sides?

Symmetric magnetic stripes indicate new crust forms at the ridge. Mirror-image patterns prove crust forms equally on both sides.
Identify the plate-boundary type most consistent with a mid-ocean ridge and rising magma.

Divergent boundary. Plates separate where magma creates new oceanic crust.
Which seafloor feature is most directly associated with subduction of oceanic crust?

Deep-ocean trench. Where oceanic plates bend down and sink into the mantle.
Which seafloor measurement pattern indicates plates move away from a mid-ocean ridge?

Heat flow is highest at the ridge and decreases outward. Hot magma at ridges cools as plates move away.
Which option best supports seafloor spreading: magnetic stripes random or mirrored across a ridge?

Mirrored (symmetrical) across the ridge. Symmetry proves new crust forms equally on both sides.
Which seafloor observation best supports that the Mid-Atlantic Ridge is spreading apart?

symmetrical magnetic stripes on both sides of the ridge. Mirror-image patterns prove new crust forms equally on both sides.
What is the name of the former supercontinent that included most modern continents?

Pangaea. The supercontinent existed about 250 million years ago before breaking apart.
Choose the correct interpretation: magnetic stripes on both sides of a ridge match in order or are random?

They match in order on both sides. Symmetrical patterns prove systematic spreading from the ridge.
What is Pangaea in the context of plate motion evidence?

A former supercontinent containing most landmasses. All continents were joined ~250 million years ago.
Which seafloor feature provides evidence that old oceanic crust is recycled back into the mantle?

Deep-ocean trench at a subduction zone. Old oceanic crust descends and melts, completing the rock cycle.
Which plate-boundary type is indicated by a mid-ocean ridge?

Divergent boundary. Plates move apart at ridges, creating new oceanic crust.
What magnetic pattern in seafloor basalt provides strong evidence for seafloor spreading?

Symmetrical magnetic stripes parallel to the mid-ocean ridge. Earth's magnetic reversals recorded as crust forms at ridges.
What type of evidence uses the matching outlines of continents to support plate motion?

Continental fit (jigsaw-fit) evidence. Matching coastlines suggest continents were once joined and drifted apart.
What plate motion is indicated when a deep-ocean trench is present along a plate boundary?

Convergent motion with subduction. Trenches only form where one plate descends under another.
What is the name of the past supercontinent formed when most landmasses were connected?

Pangaea. This supercontinent existed about 250 million years ago before breaking apart.
Identify the plate-boundary type if a ridge is offset by sideways breaks that cut across the seafloor.

transform boundary (transform faults). Plates slide past each other horizontally at these fracture zones.
What seafloor pattern of magnetism supports seafloor spreading?

Symmetrical magnetic stripes on both sides of a ridge. Magnetic reversals create mirror-image patterns as new crust forms.
What is the term for the idea that continents were once joined and later moved apart?

Continental drift. Wegener's theory explaining how continents fit together like puzzle pieces.
Which direction does oceanic crust move relative to a mid-ocean ridge during spreading?

Away from the ridge on both sides. New crust pushes older crust outward in both directions.
What is the name of the supercontinent that included most of Earth's land about 300 million years ago?

Pangaea. Greek for "all Earth," it broke apart into today's continents.
What seafloor feature is a deep, narrow depression where oceanic crust sinks into the mantle?

deep-ocean trench. Forms where denser oceanic crust descends beneath another plate.
Identify the seafloor feature that offsets segments of a mid-ocean ridge in a step-like pattern.

Transform fault. Lateral sliding motion creates these perpendicular fractures.
What is seafloor spreading?

Creation and outward movement of oceanic crust from ridges. Process where new ocean floor forms and pushes older crust away.
Identify the key evidence from seafloor magnetism that shows new crust forms at ridges.

Matching magnetic stripe ages mirrored across the ridge. Symmetrical patterns prove simultaneous formation and spreading.
What is the term for the idea that today's continents were once joined as one landmass?

Continental drift. Wegener's hypothesis that continents moved over time.
What is a deep-ocean trench?

A deep seafloor valley where subduction occurs. Formed when denser oceanic plate sinks beneath another plate.
What is the name of the underwater mountain chain that marks many divergent plate boundaries?

Mid-ocean ridge. Forms where plates diverge and new oceanic crust is created.
What is the best evidence-based reason coastlines do not match perfectly for continental fit?

Erosion and deposition have changed coastlines over time. Millions of years of weathering altered original continental edges.
Which plate boundary type is indicated by a mid-ocean ridge and seafloor spreading?

Divergent plate boundary. Plates move apart, creating new crust at the ridge.
Which seafloor feature is a deep, narrow depression that marks where a plate sinks into the mantle?

Deep-ocean trench. Forms where denser oceanic plate subducts beneath another plate.
Identify the plate motion if two continents fit together and matching fossils occur on both sides of an ocean.

The continents moved apart from a former connection. Matching shapes and fossils indicate past connection before separation.
What is the name of the ancient supercontinent proposed from matching continental shapes and other evidence?

Pangaea. All continents were united ~250 million years ago.
Identify the plate boundary type commonly associated with deep-ocean trenches and subduction.

Convergent plate boundary. Plates collide here, often causing one to sink beneath the other.
What seafloor feature is a long underwater mountain chain where new ocean crust forms?

Mid-ocean ridge. Forms at divergent boundaries where plates separate and magma rises.
What seafloor feature is most strongly associated with subduction at a convergent boundary?

Deep-ocean trench. Forms where oceanic plate descends beneath another plate.
Which continental feature fit is more reliable than coastline fit for matching continents?

Continental shelf edges (true continental margins). Shelf edges show the true continent boundary, not just the waterline.
What type of plate boundary is indicated by transform faults that cut across mid-ocean ridges?

Transform plate boundary (plates slide past each other). Transform faults show lateral movement between plates.
Identify the seafloor age trend that supports seafloor spreading away from a mid-ocean ridge.

ocean crust is youngest at the ridge and older farther away. Age increases symmetrically away from ridges, proving seafloor spreading.
Which observation about South America and Africa supports past connection of continents?

Their coastlines fit together like puzzle pieces. The eastern bulge of S. America fits into Africa's western curve.
What is the process called when new oceanic crust forms at mid-ocean ridges and moves outward?

Seafloor spreading. New crust forms at the ridge center and moves outward like a conveyor belt.
Which boundary type is indicated by offset ridge segments and frequent shallow earthquakes?

Transform boundary. Plates slide laterally past each other.
Which boundary type best matches the seafloor feature: a mid-ocean ridge?

Divergent boundary. Ridges mark where plates separate and new crust forms.
What does symmetrical magnetic striping on both sides of a ridge indicate about seafloor age?

Crust is youngest at the ridge and older farther away. New crust forms continuously at ridge, pushing older crust outward symmetrically.
What type of evidence is shown when South America and Africa appear to fit together like puzzle pieces?

Matching continental shapes (continental fit) suggests past connection. Similar coastlines indicate continents were once joined.
Which plate-boundary type is indicated by a deep-ocean trench?

Convergent boundary (subduction zone). Trenches form where oceanic plates sink at convergent boundaries.
Which seafloor evidence shows that oceanic crust is recycled rather than getting endlessly older?

Ocean crust is youngest at ridges and destroyed at trenches. This recycling prevents ocean floor from being billions of years old.
What is a transform fault on the seafloor, in terms of plate motion?

A boundary where plates slide past each other. Plates move horizontally past each other without creating/destroying crust.
What process adds new oceanic crust at a mid-ocean ridge and moves plates apart?

seafloor spreading. New crust forms at ridges, pushing older crust outward in both directions.
Which option best describes the age of oceanic crust as distance from a mid-ocean ridge increases?

Oceanic crust gets older with increasing distance from the ridge. Dating shows progressive aging away from spreading centers.

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