what does this suggest about the rate of seafloor spreading compared to the rate of subduction?

Seafloor spreading and other tectonic activity processes are the result of drape convection. Drape convection is the slow, churning move of Earth's drapery. Convection currents comport heat from the lower mantle and core to the lithosphere. Convection currents besides "recycle" lithospheric materials back to the mantle.

Seafloor spreading occurs at divergent plate boundaries. As tectonic plates slowly move away from each other, heat from the drape's convection currents makes the chaff more plastic and less dense. The less-dense material rises, ofttimes forming a mountain or elevated area of the seafloor.

Eventually, the crust cracks. Hot magma fueled by mantle convection bubbles up to fill up these fractures and spills onto the chaff. This bubbled-up magma is cooled past frigid seawater to form igneous rock. This rock (basalt) becomes a new office of World'due south crust.

Mid-Body of water Ridges

Seafloor spreading occurs along mid-ocean ridges—large mountain ranges ascent from the ocean floor. The Mid-Atlantic Ridge, for example, separates the North American plate from the Eurasian plate, and the South American plate from the African plate. The East Pacific Rise is a mid-sea ridge that runs through the eastern Pacific Ocean and separates the Pacific plate from the North American plate, the Cocos plate, the Nazca plate, and the Antarctic plate. The Southeast Indian Ridge marks where the southern Indo-Australian plate forms a divergent boundary with the Antarctic plate.

Seafloor spreading is non consistent at all mid-body of water ridges. Slowly spreading ridges are the sites of tall, narrow underwater cliffs and mountains. Chop-chop spreading ridges have a much more than gentle slopes.

The Mid-Atlantic Ridge, for case, is a slow spreading middle. It spreads ii-five centimeters (.8-2 inches) every year and forms an ocean trench about the size of the Grand Canyon. The East Pacific Rise, on the other mitt, is a fast spreading center. It spreads about vi-16 centimeters (3-half dozen inches) every year. There is non an ocean trench at the E Pacific Rise, considering the seafloor spreading is too rapid for i to develop!

The newest, thinnest crust on Globe is located about the center of mid-ocean ridge—the bodily site of seafloor spreading. The age, density, and thickness of oceanic crust increases with distance from the mid-ocean ridge.

Geomagnetic Reversals

The magnetism of mid-body of water ridges helped scientists first identify the process of seafloor spreading in the early 20th century. Basalt, the once-molten rock that makes up most new oceanic crust, is a adequately magnetic substance, and scientists began using magnetometers to measure the magnetism of the ocean floor in the 1950s. What they discovered was that the magnetism of the ocean flooring around mid-ocean ridges was divided into matching "stripes" on either side of the ridge. The specific magnetism of basalt rock is determined by the Earth's magnetic field when the magma is cooling.

Scientists determined that the same process formed the perfectly symmetrical stripes on both side of a mid-ocean ridge. The continual process of seafloor spreading separated the stripes in an orderly pattern.

Geographic Features

Oceanic chaff slowly moves away from mid-ocean ridges and sites of seafloor spreading. Equally it moves, information technology becomes cooler, more than dense, and more than thick. Eventually, older oceanic crust encounters a tectonic purlieus with continental chaff.

In some cases, oceanic chaff encounters an active plate margin. An active plate margin is an actual plate purlieus, where oceanic chaff and continental crust crash into each other. Agile plate margins are oft the site of earthquakes and volcanoes. Oceanic chaff created by seafloor spreading in the East Pacific Rise, for instance, may become function of the Ring of Fire, the horseshoe-shaped design of volcanoes and earthquake zones effectually the Pacific body of water bowl.

In other cases, oceanic crust encounters a passive plate margin. Passive margins are not plate boundaries, merely areas where a unmarried tectonic plate transitions from oceanic lithosphere to continental lithosphere. Passive margins are non sites of faults or subduction zones. Thick layers of sediment overlay the transitional crust of a passive margin. The oceanic chaff of the Mid-Atlantic Ridge, for instance, will either become function of the passive margin on the North American plate (on the east coast of North America) or the Eurasian plate (on the west coast of Europe).

New geographic features can be created through seafloor spreading. The Red Body of water, for case, was created as the African plate and the Arabian plate tore abroad from each other. Today, only the Sinai Peninsula connects the Middle East (Asia) with North Africa. Eventually, geologists predict, seafloor spreading will completely split the 2 continents—and join the Red and Mediterranean Seas.

Mid-ocean ridges and seafloor spreading can also influence body of water levels. As oceanic crust moves away from the shallow mid-bounding main ridges, it cools and sinks as information technology becomes more dense. This increases the volume of the bounding main bowl and decreases the body of water level. For instance, a mid-ocean ridge system in Panthalassa—an aboriginal ocean that surrounded the supercontinent Pangaea—contributed to shallower oceans and college sea levels in the Paleozoic era. Panthalassa was an early form of the Pacific Bounding main, which today experiences less seafloor spreading and has a much less extensive mid-ocean ridge system. This helps explain why bounding main levels have fallen dramatically over the past 80 million years.

Seafloor spreading disproves an early on function of the theory of continental migrate. Supporters of continental drift originally theorized that the continents moved (drifted) through unmoving oceans. Seafloor spreading proves that the ocean itself is a site of tectonic activeness.

Keeping Globe in Shape

Seafloor spreading is just one part of plate tectonics. Subduction is another. Subduction happens where tectonic plates crash into each other instead of spreading apart. At subduction zones, the border of the denser plate subducts, or slides, beneath the less-dumbo one. The denser lithospheric fabric then melts back into the Earth's mantle.

Seafloor spreading creates new crust. Subduction destroys old chaff. The two forces roughly balance each other, so the shape and diameter of the Earth remain abiding.

Earth's newest crust is created at sites of seafloor spreading—red sites on this map.

Map courtesy NOAA

Triple Junctions

Seafloor spreading and rift valleys are common features at "triple junctions." Triple junctions are the intersection of 3 divergent plate boundaries. The triple junction is the central point where three cracks (boundaries) dissever off at well-nigh 120° angles from each other.

In the Afar Triple Junction, the African, Somali, and Arabian plates are splitting from each other. The Bang-up Rift Valley and Red Bounding main (a major site of seafloor spreading) are the upshot of plate tectonics in the Afar Triple Junction.

active plate margin

Noun

convergent tectonic plate purlieus where an oceanic plate is crashing into a continental plate.

basalt

Noun

type of dark volcanic rock.

churn

Verb

to mix vigorously or violently.

Noun

steep wall of rock, earth, or ice.

consistent

Adjective

maintaining a steady, reliable quality.

Substantive

i of the 7 main land masses on World.

continental chaff

Substantive

thick layer of Earth that sits beneath continents.

Noun

the movement of continents resulting from the motion of tectonic plates.

convection electric current

Noun

movement of a fluid from a absurd expanse to a warm area.

Substantive

the extremely hot middle of Earth, another planet, or a star.

Noun

rocky outermost layer of Earth or other planet.

dense

Adjective

having parts or molecules that are packed closely together.

bore

Substantive

width of a circle.

disprove

Verb

to evidence wrong.

divergent boundary

Noun

area where two or more tectonic plates are moving away from each other. Also chosen an extensional boundary.

earthquake

Noun

the sudden shaking of Earth'due south crust acquired past the release of energy along fault lines or from volcanic activeness.

fast spreading center

Substantive

mid-ocean ridge where seafloor spreading is occuring at more than than 100 millimeters (4 inches) a year.

fault

Noun

a crevice in the Earth's chaff where at that place has been movement.

frigid

Adjective

very cold.

geologic

Adjective

having to practise with the physical formations of the World.

geologist

Noun

person who studies the concrete formations of the Earth.

Substantive

stone formed by the cooling of magma or lava.

Noun

outer, solid portion of the World. Also called the geosphere.

Noun

molten, or partially melted, rock beneath the Globe's surface.

magnetic field

Noun

area around and afflicted by a magnet or charged particle.

Noun

force by which objects attract or repel one some other.

magnetometer

Substantive

scientific musical instrument used to measure out the presence, strength, and direction of Earth's magnetic field.

Noun

centre layer of the Earth, fabricated of by and large solid stone.

mantle convection

Noun

slow motion of Earth's solid mantle acquired by convection currents transferring heat from the interior of the Earth to the surface.

Mid-Atlantic Ridge

Noun

underwater mountain range that runs from Iceland to Antarctica.

mid-ocean ridge

Noun

underwater mountain range.

molten

Describing word

solid textile turned to liquid by rut.

mountain range

Noun

serial or chain of mountains that are close together.

ocean basin

Noun

depression in the Globe's surface located entirely beneath the ocean.

oceanic crust

Substantive

thin layer of the Earth that sits beneath ocean basins.

Substantive

a long, deep low in the bounding main floor.

Paleozoic Era

Substantive

about 541-252 million years agone.

Pangaea

Noun

supercontinent of all the Earth'south landmass that existed nearly 250 million years ago.

passive plate margin

Noun

lithospheric region where oceanic chaff transitions to continental crust without faults or subduction zones.

plastic

Noun

chemical fabric that tin be easily shaped when heated to a high temperature.

Noun

move and interaction of the Earth'southward plates.

predict

Verb

to know the outcome of a state of affairs in advance.

Noun

depression in the ground caused by the Earth's chaff spreading apart.

Noun

horseshoe-shaped string of volcanoes and earthquake sites around edges of the Pacific Body of water.

Noun

rift in underwater mount range where new oceanic chaff is formed.

Substantive

base level for measuring elevations. Sea level is determined past measurements taken over a 19-yr cycle.

seawater

Substantive

salty water from an ocean or sea.

Noun

solid material transported and deposited by water, ice, and wind.

ho-hum spreading center

Noun

mid-ocean ridge where seafloor spreading is occuring at less than 55 millimeters (two inches) a year.

subduct

Verb

to pull downwards or beneath something.

subduction zone

Noun

area where ane tectonic plate slides under another.

supercontinent

Substantive

ancient, giant landmass that split apart to course all the continents we know today.

symmetrical

Describing word

having the same system of parts on either side.

tectonic activity

Noun

movement of tectonic plates resulting in geologic activity such equally volcanic eruptions and earthquakes.

tectonic plate

Noun

massive slab of solid stone made upwardly of World's lithosphere (crust and upper mantle). As well called lithospheric plate.

theorize

Verb

to codify and suggest a group of ideas to explain a scientific question.

transition

Noun

move from one position to some other.

transitional crust

Noun

lithospheric region where oceanic chaff transitions into continental crust.

Noun

an opening in the Globe's chaff, through which lava, ash, and gases erupt, and also the cone congenital by eruptions.

volume

Noun

space an object occupies.

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Source: https://www.nationalgeographic.org/encyclopedia/seafloor-spreading/