what happens to older oceanic crust as new rock is formed during seafloor spreading?
Seafloor spreading and other tectonic activity processes are the result of drapery convection. Mantle convection is the tedious, churning movement of Earth's mantle. Convection currents carry heat from the lower mantle and core to the lithosphere. Convection currents also "recycle" lithospheric materials dorsum to the mantle. Seafloor spreading occurs at divergent plate boundaries. As tectonic plates slowly move away from each other, heat from the pall's convection currents makes the chaff more plastic and less dense. The less-dense material rises, often forming a mount or elevated surface area of the seafloor. Eventually, the crust cracks. Hot magma fueled by mantle convection bubbling upwards to fill these fractures and spills onto the crust. This bubbled-up magma is cooled by frigid seawater to form igneous rock. This rock (basalt) becomes a new part of Earth's crust. Mid-Ocean Ridges Seafloor spreading occurs along mid-ocean ridges—large mount ranges rising from the ocean floor. The Mid-Atlantic Ridge, for instance, separates the North American plate from the Eurasian plate, and the South American plate from the African plate. The Eastward Pacific Rise is a mid-ocean 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 purlieus with the Antarctic plate. Seafloor spreading is not consistent at all mid-ocean ridges. Slowly spreading ridges are the sites of tall, narrow underwater cliffs and mountains. Rapidly spreading ridges have a much more than gentle slopes. The Mid-Atlantic Ridge, for instance, is a slow spreading center. It spreads 2-5 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 hand, is a fast spreading heart. It spreads about 6-16 centimeters (3-6 inches) every twelvemonth. There is not an ocean trench at the E Pacific Ascent, because the seafloor spreading is as well rapid for ane to develop! The newest, thinnest crust on Earth is located virtually the center of mid-sea ridge—the actual site of seafloor spreading. The age, density, and thickness of oceanic chaff increases with distance from the mid-ocean ridge. Geomagnetic Reversals The magnetism of mid-ocean 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 out the magnetism of the ocean flooring in the 1950s. What they discovered was that the magnetism of the ocean floor around mid-ocean ridges was divided into matching "stripes" on either side of the ridge. The specific magnetism of basalt stone is determined past the Globe'south magnetic field when the magma is cooling. Scientists determined that the same process formed the perfectly symmetrical stripes on both side of a mid-bounding main ridge. The continual process of seafloor spreading separated the stripes in an orderly pattern. Geographic Features Oceanic crust slowly moves abroad from mid-ocean ridges and sites of seafloor spreading. Every bit it moves, information technology becomes cooler, more dumbo, and more than thick. Eventually, older oceanic crust encounters a tectonic boundary with continental crust. In some cases, oceanic crust encounters an agile plate margin. An active plate margin is an actual plate boundary, where oceanic crust and continental crust crash into each other. Agile plate margins are often the site of earthquakes and volcanoes. Oceanic crust created past seafloor spreading in the East Pacific Ascension, for case, may get part of the Band of Burn, the horseshoe-shaped pattern of volcanoes and earthquake zones around the Pacific body of water bowl. In other cases, oceanic crust encounters a passive plate margin. Passive margins are not plate boundaries, but areas where a single tectonic plate transitions from oceanic lithosphere to continental lithosphere. Passive margins are not sites of faults or subduction zones. Thick layers of sediment overlay the transitional chaff of a passive margin. The oceanic crust of the Mid-Atlantic Ridge, for example, will either become part of the passive margin on the North American plate (on the east declension of North America) or the Eurasian plate (on the west coast of Europe). New geographic features can be created through seafloor spreading. The Ruby Bounding main, for example, was created as the African plate and the Arabian plate tore away from each other. Today, merely the Sinai Peninsula connects the Middle E (Asia) with North Africa. Eventually, geologists predict, seafloor spreading will completely separate the 2 continents—and bring together the Red and Mediterranean Seas. Mid-body of water ridges and seafloor spreading can also influence sea levels. Every bit oceanic crust moves away from the shallow mid-ocean ridges, it cools and sinks as it becomes more dumbo. This increases the book of the ocean basin and decreases the sea level. For case, a mid-ocean ridge system in Panthalassa—an ancient bounding main that surrounded the supercontinent Pangaea—contributed to shallower oceans and higher sea levels in the Paleozoic era. Panthalassa was an early class of the Pacific Ocean, which today experiences less seafloor spreading and has a much less all-encompassing mid-ocean ridge arrangement. This helps explain why sea levels have fallen dramatically over the past 80 meg years. Seafloor spreading disproves an early part of the theory of continental drift. 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 activity. Keeping Earth in Shape Seafloor spreading is only one part of plate tectonics. Subduction is another. Subduction happens where tectonic plates crash into each other instead of spreading autonomously. At subduction zones, the border of the denser plate subducts, or slides, beneath the less-dense one. The denser lithospheric material then melts back into the Earth's mantle. Seafloor spreading creates new crust. Subduction destroys one-time crust. The two forces roughly balance each other, then the shape and diameter of the Globe remain constant.
Earth's newest chaff is created at sites of seafloor spreading—cherry-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 three divergent plate boundaries. The triple junction is the primal point where three cracks (boundaries) split up off at about 120° angles from each other.
In the Afar Triple Junction, the African, Somali, and Arabian plates are splitting from each other. The Slap-up Rift Valley and Red Sea (a major site of seafloor spreading) are the result of plate tectonics in the Distant Triple Junction.
active plate margin
Substantive
convergent tectonic plate boundary where an oceanic plate is crashing into a continental plate.
basalt
Noun
type of dark volcanic stone.
churn
Verb
to mix vigorously or violently.
Noun
steep wall of stone, earth, or ice.
consistent
Adjective
maintaining a steady, reliable quality.
Noun
1 of the seven main land masses on Earth.
continental chaff
Noun
thick layer of Earth that sits beneath continents.
Substantive
the movement of continents resulting from the motility of tectonic plates.
convection current
Noun
movement of a fluid from a cool expanse to a warm area.
Noun
the extremely hot center 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
Noun
width of a circle.
disprove
Verb
to prove wrong.
divergent boundary
Noun
area where two or more than tectonic plates are moving away from each other. Also called an extensional boundary.
earthquake
Noun
the sudden shaking of Earth'due south chaff caused by the release of free energy along mistake lines or from volcanic activity.
fast spreading center
Noun
mid-ocean ridge where seafloor spreading is occuring at more than 100 millimeters (4 inches) a year.
mistake
Substantive
a fissure in the Globe's crust where there has been movement.
frigid
Adjective
very common cold.
geologic
Describing word
having to do with the physical formations of the Earth.
geologist
Noun
person who studies the concrete formations of the World.
Noun
rock formed by the cooling of magma or lava.
Noun
outer, solid portion of the Globe. Likewise chosen the geosphere.
Noun
molten, or partially melted, stone beneath the Earth's surface.
magnetic field
Substantive
expanse around and affected by a magnet or charged particle.
Noun
forcefulness by which objects attract or repel one some other.
magnetometer
Noun
scientific instrument used to measure the presence, strength, and direction of World's magnetic field.
Noun
eye layer of the Earth, fabricated of mostly solid stone.
drape convection
Noun
wearisome movement of Globe's solid drapery caused by convection currents transferring heat from the interior of the Globe to the surface.
Mid-Atlantic Ridge
Noun
underwater mountain range that runs from Iceland to Antarctica.
mid-ocean ridge
Noun
underwater mountain range.
molten
Adjective
solid fabric turned to liquid by estrus.
mount range
Substantive
serial or chain of mountains that are close together.
ocean bowl
Noun
low in the World'southward surface located entirely beneath the bounding main.
oceanic chaff
Substantive
thin layer of the Earth that sits beneath body of water basins.
Noun
a long, deep low in the sea floor.
Paleozoic Era
Substantive
most 541-252 million years ago.
Pangaea
Noun
supercontinent of all the Globe'south landmass that existed about 250 million years ago.
passive plate margin
Noun
lithospheric region where oceanic chaff transitions to continental crust without faults or subduction zones.
plastic
Substantive
chemic material that tin be easily shaped when heated to a high temperature.
Noun
motility and interaction of the Earth'due south plates.
predict
Verb
to know the outcome of a situation in advance.
Substantive
depression in the ground caused by the Earth's crust spreading autonomously.
Noun
horseshoe-shaped string of volcanoes and convulsion sites around edges of the Pacific Ocean.
Noun
rift in underwater mountain range where new oceanic crust is formed.
Noun
base level for measuring elevations. Bounding main level is determined past measurements taken over a 19-twelvemonth wheel.
seawater
Noun
salty water from an ocean or sea.
Noun
solid material transported and deposited by h2o, water ice, and wind.
slow spreading center
Noun
mid-ocean ridge where seafloor spreading is occuring at less than 55 millimeters (ii inches) a year.
subduct
Verb
to pull downwardly or beneath something.
subduction zone
Noun
area where 1 tectonic plate slides under some other.
supercontinent
Noun
ancient, behemothic landmass that split apart to form all the continents we know today.
symmetrical
Describing word
having the aforementioned arrangement of parts on either side.
tectonic activity
Substantive
movement of tectonic plates resulting in geologic activeness such as volcanic eruptions and earthquakes.
tectonic plate
Noun
massive slab of solid rock made up of World'southward lithosphere (chaff and upper drape). Also called lithospheric plate.
theorize
Verb
to formulate and propose a group of ideas to explicate a scientific question.
transition
Substantive
movement from one position to another.
transitional crust
Noun
lithospheric region where oceanic crust transitions into continental crust.
Noun
an opening in the Earth'southward crust, through which lava, ash, and gases erupt, and also the cone built by eruptions.
book
Noun
infinite an object occupies.
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Source: https://www.nationalgeographic.org/encyclopedia/seafloor-spreading/#:~:text=Oceanic%20crust%20slowly%20moves%20away,tectonic%20boundary%20with%20continental%20crust.