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70-665: The Norfolk Ridge (Norfolk Island Ridge, Norfolk Rise, South New Caledonia Ridge) is a long submarine ridge running between New Caledonia and New Zealand , about 1,300 km (810 mi) off the east-coast of Australia . It is part of a complex region of ridges between the oceanic crust of the Pacific plate and the continental crust of Australia. Little has been known about the Norfolk Ridge; however, it generally lies about 1,000–1,200 m (3,300–3,900 ft) below sea level and consists of Late Cretaceous continental crust . It

140-464: A common feature at oceanic spreading centers. A feature of the elevated ridges is their relatively high heat flow values, of about 1–10 μcal/cm s, or roughly 0.04–0.4 W/m . Most crust in the ocean basins is less than 200 million years old, which is much younger than the 4.54 billion year age of Earth . This fact reflects the process of lithosphere recycling into the Earth's mantle during subduction . As

210-515: A crustal thickness of 7 km (4.3 mi), this amounts to about 19 km (4.6 cu mi) of new ocean crust formed every year. Baseball (ball) A baseball is the ball used in the sport of baseball . It consists of a rubber or cork center wrapped in yarn and covered with white natural horsehide or cowhide , or a synthetic composite leather. A regulation baseball is 9 to 9.25 inches (229 to 235 mm) in circumference i.e. 2.86 to 2.94 inches (73 to 75 mm) in diameter, with

280-417: A looser winding (known as "dead balls") did not travel as far or fast. This is generally true for all baseballs. Teams often used this knowledge to their advantage, as players from the team usually manufactured their own baseballs to use in games. There is no agreement on who invented the commonplace figure-8 stitching on baseballs. Some historians say it was invented by Ellis Drake, a shoemaker's son, to make

350-729: A negligible portion of a modern MLB team's operating budget. Recreational-grade baseballs can be purchased by the public for an even lower unit price. Once discarded by the umpire, game-used baseballs not hit into the stands are collected by batboys . Many baseballs involved in historical plays are displayed at the National Baseball Hall of Fame and Museum in Cooperstown , New York . Other baseballs associated with noteworthy in-game events are often authenticated and sold as memorabilia . Most such sales today are conducted on MLB's official website. The total proceeds from such sales represent

420-542: A rubber core from old, melted shoes, wrapped in yarn and leather. Fish eyes were also used as cores in some places. Pitchers usually made their own balls, which were used throughout the game, softening and coming unraveled as the game went on. One of the more popular earlier ball designs was the "lemon peel ball," named after its distinct four lines of stitching design. Lemon peel balls were darker, smaller, and weighed less than other baseballs, prompting them to travel further and bounce higher, causing very high-scoring games. In

490-546: A ship of the Lamont–Doherty Earth Observatory of Columbia University , traversed the Atlantic Ocean, recording echo sounder data on the depth of the ocean floor. A team led by Marie Tharp and Bruce Heezen concluded that there was an enormous mountain chain with a rift valley at its crest, running up the middle of the Atlantic Ocean. Scientists named it the 'Mid-Atlantic Ridge'. Other research showed that

560-489: A significant portion of the total purchase cost of baseballs since even balls used for relatively minor accomplishments can each fetch hundreds or thousands of dollars. In 1909, sports magnate and former player Alfred J. Reach patented the ivory centered "ivory nut" in Panama and suggested it might be even better in a baseball than cork. However, Philadelphia Athletics president Benjamin F. Shibe , who had invented and patented

630-408: A subduction zone drags the rest of the plate along behind it. The slab pull mechanism is considered to be contributing more than the ridge push. A process previously proposed to contribute to plate motion and the formation of new oceanic crust at mid-ocean ridges is the "mantle conveyor" due to deep convection (see image). However, some studies have shown that the upper mantle ( asthenosphere )

700-414: A unit price which would be equal to $ 110 today. Due to their high relative cost, club owners in the early 20th century were reluctant to spend much money on new balls if not necessary. It was not unusual for a single baseball to last an entire game, nor for a baseball to be reused for the next game especially if it was still in relatively good condition as would likely be the case for a ball introduced late in

770-411: A weight of 5 to 5.25 ounces (0.142 to 0.149 kg). The leather cover is commonly formed from two saddle-shaped pieces stitched together, typically with red-dyed thread. There are 108 stitches on a regulation baseball. That stitching plays a significant role in the trajectory of a thrown baseball due to the drag caused by the interaction between the stitching and the air. Controlling the orientation of

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840-449: A well-known baseball pitcher who made his own balls, convinced the NL to adopt his ball as the official baseball for the NL. It remained that way for a century. In 1910, the cork-core ball was introduced. They outlasted rubber core baseballs; and for the first few years they were used, balls were hit further and faster than rubber core balls. Pitchers adapted with the use of the spitball , which

910-420: Is a global scale ion-exchange system. Hydrothermal vents at spreading centers introduce various amounts of iron , sulfur , manganese , silicon , and other elements into the ocean, some of which are recycled into the ocean crust. Helium-3 , an isotope that accompanies volcanism from the mantle, is emitted by hydrothermal vents and can be detected in plumes within the ocean. Fast spreading rates will expand

980-443: Is in a constant state of 'renewal' at the mid-ocean ridges by the processes of seafloor spreading and plate tectonics. New magma steadily emerges onto the ocean floor and intrudes into the existing ocean crust at and near rifts along the ridge axes. The rocks making up the crust below the seafloor are youngest along the axis of the ridge and age with increasing distance from that axis. New magma of basalt composition emerges at and near

1050-526: Is no evidence of the allochthons that are found in New Caledonia and Northland, except for one limited nappe area on the ridge's eastern flank. The limited rocks dredged include undated andesitic to trachyandesitic lava, a 26.3 ± 0.1  Ma shoshonite , 23 – 16 Ma or probable Pliocene limestone , Cretaceous black shales , late Eocene mudstone and middle to late Eocene sedimentary breccias . There are at least seven seamounts located on

1120-402: Is now illegal, and an emphasis on changing the ball. In 1920, a couple of important changes were made to baseballs. They began to be made using machine winders and a higher grade of yarn from Australia . Offensive statistics rose immediately, and players and fans alike believed the new balls helped batters hit the ball further. In 1925, Milton Reach patented his "cushion cork" center. It

1190-464: Is part of Zealandia , a continent that was submerged 60-85 million years ago. The Norfolk Ridge is about 1,500 km (930 mi) long and is up to 100 km (62 mi) wide. It is between the New Caledonia Trough and Norfolk Basin which has central and southern parts. The Norfolk Ridge emerges above the sea surface at Grande Terre of New Caledonia , Norfolk Island , and part of

1260-470: Is the result of changes in the volume of the ocean basins which are, in turn, affected by rates of seafloor spreading along the mid-ocean ridges. The 100 to 170 meters higher sea level of the Cretaceous Period (144–65 Ma) is partly attributed to plate tectonics because thermal expansion and the absence of ice sheets only account for some of the extra sea level. Seafloor spreading on mid-ocean ridges

1330-440: Is too plastic (flexible) to generate enough friction to pull the tectonic plate along. Moreover, mantle upwelling that causes magma to form beneath the ocean ridges appears to involve only its upper 400 km (250 mi), as deduced from seismic tomography and observations of the seismic discontinuity in the upper mantle at about 400 km (250 mi). On the other hand, some of the world's largest tectonic plates such as

1400-451: Is underlain by denser material and is deeper. Spreading rate is the rate at which an ocean basin widens due to seafloor spreading. Rates can be computed by mapping marine magnetic anomalies that span mid-ocean ridges. As crystallized basalt extruded at a ridge axis cools below Curie points of appropriate iron-titanium oxides, magnetic field directions parallel to the Earth's magnetic field are recorded in those oxides. The orientations of

1470-605: Is very dangerous to throw because it is so slick and hard. By rule, balls used in the professional game must be rubbed with a mud known as "rubbing mud" , which is typically applied either by the umpires or someone working under their supervision before each game, and is intended to help the pitcher's grip. Because the mud discolors the ball, many fans prefer to purchase non-game-used balls for purposes such as collecting autographs, etc. In contrast, recreational-grade baseballs are designed so as not to require any special preparation before being used. Three common forms of baseball exist:

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1540-569: The North American plate and South American plate are in motion, yet only are being subducted in restricted locations such as the Lesser Antilles Arc and Scotia Arc , pointing to action by the ridge push body force on these plates. Computer modeling of the plates and mantle motions suggest that plate motion and mantle convection are not connected, and the main plate driving force is slab pull. Increased rates of seafloor spreading (i.e.

1610-552: The Pine Tar Incident in the 1980s was one famous incident triggered by a capricious enforcement of an obscure one. Today, MLB teams are required to have a minimum of 156 baseballs ready for use in each game. When combined with baseballs needed for practice, etc. each MLB team uses tens of thousands of balls every season. However, modern professional-grade baseballs purchased in bulk as is the case with professional teams only cost about seven dollars each as of 2024 and thus make up

1680-463: The Southwest Indian Ridge ). The spreading center or axis commonly connects to a transform fault oriented at right angles to the axis. The flanks of mid-ocean ridges are in many places marked by the inactive scars of transform faults called fracture zones . At faster spreading rates the axes often display overlapping spreading centers that lack connecting transform faults. The depth of

1750-461: The longest mountain range in the world. The continuous mountain range is 65,000 km (40,400 mi) long (several times longer than the Andes , the longest continental mountain range), and the total length of the oceanic ridge system is 80,000 km (49,700 mi) long. At the spreading center on a mid-ocean ridge, the depth of the seafloor is approximately 2,600 meters (8,500 ft). On

1820-400: The 1920 death of batter Ray Chapman after being hit in the head by a pitch, perhaps due to his difficulty in seeing the ball during twilight, an effort was made to replace dirty or worn baseballs. However, even though scores of new balls are used nowadays in every game, some rules intended solely to reduce the frequency (and associated expense) of replacing balls during a game remain in force -

1890-681: The East Pacific Rise lack rift valleys. The spreading rate of the North Atlantic Ocean is ~ 25 mm/yr, while in the Pacific region, it is 80–145 mm/yr. The highest known rate is over 200 mm/yr in the Miocene on the East Pacific Rise. Ridges that spread at rates <20 mm/yr are referred to as ultraslow spreading ridges (e.g., the Gakkel Ridge in the Arctic Ocean and

1960-664: The Mid-Atlantic Ridge have spread much less far (showing a steeper profile) than faster ridges such as the East Pacific Rise (gentle profile) for the same amount of time and cooling and consequent bathymetric deepening. Slow-spreading ridges (less than 40 mm/yr) generally have large rift valleys , sometimes as wide as 10–20 km (6.2–12.4 mi), and very rugged terrain at the ridge crest that can have relief of up to 1,000 m (3,300 ft). By contrast, fast-spreading ridges (greater than 90 mm/yr) such as

2030-457: The National League president's signature in black ink. Bob Feller stated that when he was a rookie in the 1930s, National League baseball laces were black, intertwined with red; American League baseball laces were blue and red. In 2000, Major League Baseball reorganized its structure to eliminate the position of league presidents, and switched to one ball specification for both leagues. Under

2100-427: The asthenosphere at ocean trenches . Two processes, ridge-push and slab pull , are thought to be responsible for spreading at mid-ocean ridges. Ridge push refers to the gravitational sliding of the ocean plate that is raised above the hotter asthenosphere, thus creating a body force causing sliding of the plate downslope. In slab pull the weight of a tectonic plate being subducted (pulled) below an overlying plate at

2170-478: The axis because of decompression melting in the underlying Earth's mantle . The isentropic upwelling solid mantle material exceeds the solidus temperature and melts. The crystallized magma forms a new crust of basalt known as MORB for mid-ocean ridge basalt, and gabbro below it in the lower oceanic crust . Mid-ocean ridge basalt is a tholeiitic basalt and is low in incompatible elements . Hydrothermal vents fueled by magmatic and volcanic heat are

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2240-490: The axis changes in a systematic way with shallower depths between offsets such as transform faults and overlapping spreading centers dividing the axis into segments. One hypothesis for different along-axis depths is variations in magma supply to the spreading center. Ultra-slow spreading ridges form both magmatic and amagmatic (currently lack volcanic activity) ridge segments without transform faults. Mid-ocean ridges exhibit active volcanism and seismicity . The oceanic crust

2310-447: The baseball. Generally a tighter-wound baseball will leave the bat faster, and fly further. Since the baseballs used today are wound tighter than in previous years, notably the dead-ball era that prevailed through 1920, people often say the ball is " juiced " . The height of the seams also affects how well a pitcher can pitch. Baseballs used in MLB and the top minor leagues (AAA) are made to

2380-491: The bounce in the balls and that after extensive testing, "... we are comfortable that these baseballs meet all of our performance specifications." The same memo also noted that more teams had applied for permission to use humidors to store their baseballs. As of 2020 only the Arizona Diamondbacks , Boston Red Sox , Colorado Rockies , and Seattle Mariners , were using the devices. Cushioned wood cores were patented in

2450-429: The change back to the regular ball and return of players from active duty. In 1974 , due to a shortage of the material, horsehide was replaced by the more abundant cowhide as the cover material. In 1976 , MLB ended its relationship with Spalding for manufacturing their baseballs and switched to Rawlings , which still provides the balls to MLB today. A significant increase in the number of home runs since

2520-545: The compromise. During World War II , the United States banned the use of rubber for non war-related goods, including for baseballs. So in 1943 , instead of using rubber, baseballs were made with rubber-like shells of balata (also used in golf balls), which is obtained from a particular type of tropical tree . Hitting declined significantly that year. The introduction of synthetic rubber in 1944 resulted in baseballs returning to normal. Offense would return to normal after

2590-491: The continued use of hand-made balls. The raw materials are imported from the United States, assembled into baseballs and shipped back. Throughout the 20th Century, Major League Baseball used two technically identical but differently marked balls. The American League had "Official American League" and the American League's president's signature in blue ink, while National League baseballs had "Official National League" and

2660-494: The cork centered ball, commented, "I look for the leagues to adopt an 'ivory nut' baseball just as soon as they adopt a ferro-concrete bat and a base studded with steel spikes ." Both leagues adopted Shibe's cork-centered ball in 1910. The official major league ball is made by Rawlings , which produces the stitched balls in Costa Rica . Attempts to automate the manufacturing process were never entirely successful, leading to

2730-520: The cover stronger and more durable. Others say it was invented by Colonel William A. Cutler and sold to William Harwood in 1858. Harwood built the nation's first baseball factory in Natick, Massachusetts , and was the first to popularize and mass-produce baseballs with the figure-8 design. In 1876, the National League (NL) was created, and standard rules and regulations were put in place. A.G. Spalding ,

2800-401: The current rules, a major league baseball weighs between 5 and 5 + 1 ⁄ 4 ounces (142 and 149 g), and is 9 to 9 + 1 ⁄ 4 inches (229–235 mm) in circumference ( 2 + 7 ⁄ 8 –3 in or 73–76 mm in diameter). There are 108 double stitches on a baseball, or 216 individual stitches. While the decision whether to discard a baseball is formally at

2870-407: The discovery of the worldwide extent of the mid-ocean ridge in the 1950s, geologists faced a new task: explaining how such an enormous geological structure could have formed. In the 1960s, geologists discovered and began to propose mechanisms for seafloor spreading . The discovery of mid-ocean ridges and the process of seafloor spreading allowed for Wegener's theory to be expanded so that it included

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2940-411: The discretion of the home plate umpire, today baseballs are expected to be immediately replaced after even minor scratches, discoloration and undesirable texture that can occur during the game. Balls used for pre-game warm-ups are often given to fans. Because baseballs are almost always replaced after each half-inning it is increasingly customary for players to give balls used to end half-innings to fans in

3010-530: The field preserved in the oceanic crust comprise a record of directions of the Earth's magnetic field with time. Because the field has reversed directions at known intervals throughout its history, the pattern of geomagnetic reversals in the ocean crust can be used as an indicator of age; given the crustal age and distance from the ridge axis, spreading rates can be calculated. Spreading rates range from approximately 10–200 mm/yr. Slow-spreading ridges such as

3080-469: The floor of the Atlantic, as it keeps spreading, is continuously tearing open and making space for fresh, relatively fluid and hot sima [rising] from depth". However, Wegener did not pursue this observation in his later works and his theory was dismissed by geologists because there was no mechanism to explain how continents could plow through ocean crust , and the theory became largely forgotten. Following

3150-429: The front rows, either by handing the ball to a fan (especially a child) in the front row or by gently tossing it into the stands, especially if the player holding it is a home team player close to the stands as for example is often the case for an outfielder catching a fly ball. MLB has long recognized any ball that comes into the possession of a spectator by any lawful means after entering the stands as immediately becoming

3220-443: The game. Balls hit into the stands were retrieved by team employees in order to be put back in play, as is still done today in some other sports. Over the course of a game, a typical ball would become discolored due to dirt, and often tobacco juice and other materials applied by players; damage would also occur, causing slight rips and seam bursts. This would lower the offense during the games giving pitchers an advantage. However, after

3290-478: The globe are linked by plate tectonic boundaries and the trace of the ridges across the ocean floor appears similar to the seam of a baseball . The mid-ocean ridge system thus is the longest mountain range on Earth, reaching about 65,000 km (40,000 mi). The mid-ocean ridges of the world are connected and form the Ocean Ridge, a single global mid-oceanic ridge system that is part of every ocean , making it

3360-401: The late 19th century by sports equipment manufacturer Spalding , the company founded by former baseball star A.G. Spalding . In recent years, various synthetic materials have been used to create baseballs; however, they are generally considered lower quality, stitched with two red thick thread, and are not used in the major leagues . Using different types of materials affects the performance of

3430-418: The mid-1850s, teams in and around New York met in an attempt to standardize the baseball. They decided to regulate the weight of baseballs at 5 1 ⁄ 2 –6 oz, and with a circumference of 8–11 inches. There were still many variations of baseballs since they were completely handmade . Balls with more rubber and a tighter winding went further and faster (known as "live balls"), and balls with less rubber and

3500-532: The mid-ocean ridge causing basalt reactions with seawater to happen more rapidly. The magnesium/calcium ratio will be lower because more magnesium ions are being removed from seawater and consumed by the rock, and more calcium ions are being removed from the rock and released into seawater. Hydrothermal activity at the ridge crest is efficient in removing magnesium. A lower Mg/Ca ratio favors the precipitation of low-Mg calcite polymorphs of calcium carbonate ( calcite seas ). Slow spreading at mid-ocean ridges has

3570-535: The mid-ocean ridge from the South Atlantic into the Indian Ocean early in the twentieth century. Although the first-discovered section of the ridge system runs down the middle of the Atlantic Ocean, it was found that most mid-ocean ridges are located away from the center of other ocean basins. Alfred Wegener proposed the theory of continental drift in 1912. He stated: "the Mid-Atlantic Ridge ... zone in which

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3640-402: The movement of oceanic crust as well as the continents. Plate tectonics was a suitable explanation for seafloor spreading, and the acceptance of plate tectonics by the majority of geologists resulted in a major paradigm shift in geological thinking. It is estimated that along Earth's mid-ocean ridges every year 2.7 km (1.0 sq mi) of new seafloor is formed by this process. With

3710-512: The northern North Island of New Zealand . At about 31°S proceeding towards New Zealand, the ridge widens and splits into the Reinga Ridge and West Norfolk Ridge, which are separated by the Reinga Basin. The geology has only been well characterised near Grande Terre, Norfolk Island and near Northland but there is now sufficient evidence from oceanographic studies to revise the former view that

3780-403: The oceanic crust and lithosphere moves away from the ridge axis, the peridotite in the underlying mantle lithosphere cools and becomes more rigid. The crust and the relatively rigid peridotite below it make up the oceanic lithosphere , which sits above the less rigid and viscous asthenosphere . The oceanic lithosphere is formed at an oceanic ridge, while the lithosphere is subducted back into

3850-451: The opposite effect and will result in a higher Mg/Ca ratio favoring the precipitation of aragonite and high-Mg calcite polymorphs of calcium carbonate ( aragonite seas ). Experiments show that most modern high-Mg calcite organisms would have been low-Mg calcite in past calcite seas, meaning that the Mg/Ca ratio in an organism's skeleton varies with the Mg/Ca ratio of the seawater in which it

3920-440: The property of that spectator, although balls hit out of the park for momentous occasions (record setting, or for personal reasons) are often requested to be returned by the fan who catches or otherwise retrieves it, or donated freely by the fan. Usually, the player will give the fan an autographed bat and/or other autographed items in exchange for the special ball. Without proper preparation, an official professional-grade baseball

3990-574: The rate of expansion of the mid-ocean ridge) have caused the global ( eustatic ) sea level to rise over very long timescales (millions of years). Increased seafloor spreading means that the mid-ocean ridge will then expand and form a broader ridge with decreased average depth, taking up more space in the ocean basin. This displaces the overlying ocean and causes sea levels to rise. Sealevel change can be attributed to other factors ( thermal expansion , ice melting, and mantle convection creating dynamic topography ). Over very long timescales, however, it

4060-440: The ridge crest was seismically active and fresh lavas were found in the rift valley. Also, crustal heat flow was higher here than elsewhere in the Atlantic Ocean basin. At first, the ridge was thought to be a feature specific to the Atlantic Ocean. However, as surveys of the ocean floor continued around the world, it was discovered that every ocean contains parts of the mid-ocean ridge system. The German Meteor expedition traced

4130-416: The ridge flanks, the depth of the seafloor (or the height of a location on a mid-ocean ridge above a base-level) is correlated with its age (age of the lithosphere where depth is measured). The depth-age relation can be modeled by the cooling of a lithosphere plate or mantle half-space. A good approximation is that the depth of the seafloor at a location on a spreading mid-ocean ridge is proportional to

4200-523: The same specifications, but labelled separately. Balls used in the lower minor leagues (up to AA) use slightly different specifications intended to make those balls somewhat more durable, although MLB pitchers on rehab assignments in the minors are usually supplied with major league-grade balls. Generally, in Little League through college leagues, the seams are markedly higher than balls used in professional leagues. Baseballs cost three dollars each in 1900,

4270-431: The seafloor were analyzed by oceanographers Matthew Fontaine Maury and Charles Wyville Thomson and revealed a prominent rise in the seafloor that ran down the Atlantic basin from north to south. Sonar echo sounders confirmed this in the early twentieth century. It was not until after World War II , when the ocean floor was surveyed in more detail, that the full extent of mid-ocean ridges became known. The Vema ,

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4340-572: The separating plates, and emerges as lava , creating new oceanic crust and lithosphere upon cooling. The first discovered mid-ocean ridge was the Mid-Atlantic Ridge , which is a spreading center that bisects the North and South Atlantic basins; hence the origin of the name 'mid-ocean ridge'. Most oceanic spreading centers are not in the middle of their hosting ocean basis but regardless, are traditionally called mid-ocean ridges. Mid-ocean ridges around

4410-439: The square root of the age of the seafloor. The overall shape of ridges results from Pratt isostasy : close to the ridge axis, there is a hot, low-density mantle supporting the oceanic crust. As the oceanic plate cools, away from the ridge axis, the oceanic mantle lithosphere (the colder, denser part of the mantle that, together with the crust, comprises the oceanic plates) thickens, and the density increases. Thus older seafloor

4480-416: The start of the 2016 baseball season caused MLB officials to establish a committee that would examine the manufacturing process. In December 2019, MLB officials said that a lower stitching seam profile had most likely led to the increase in home runs, but also pledged to consider studying the issue. On February 5, 2021, MLB issued a memo that said that Rawlings had altered their manufacturing process to reduce

4550-454: The stitches and the speed of the ball's rotation allows a pitcher to affect the behavior of the pitched ball in specific ways. Commonly employed pitches include the curveball , the slider , the two-seam fastball , the four-seam fastball , the sinker , the cutter and the changeup . In the early, mid-1800s days of baseball , there was a great variety in the size, shape, weight, and manufacturing of baseballs. Early baseballs were made with

4620-560: The tectonics were just those of the two ends of the ridge. The Norfolk Ridge formed as a depocenter along the eastern margin of Zealandia prior to the Eocene . This formation is suggested to be Mesozoic to early Cenozoic . The ridge itself came into being from then to the Oligocene as part of a spontaneous mode of subduction initiation associated with the Kermadec–Tonga subduction zone . This

4690-413: The western flank of the ridge with three samples from their flanks dated between 33 and 21.5 Ma. Quaternary coral reefs and intraplate basalts that are much younger at 2–3 Ma are found on Norfolk Island. Submarine ridge The production of new seafloor and oceanic lithosphere results from mantle upwelling in response to plate separation. The melt rises as magma at the linear weakness between

4760-404: Was a cork core surrounded by black rubber, then another layer of red rubber. In 1934, The National League and American League came to a compromise and standardized the baseball. They agreed on a cushion cork center; two wrappings of yarn; a special rubber cement coating; two more wrappings of yarn; and, finally, a horsehide cover. Baseballs have gone through only a few small changes since

4830-534: Was grown. The mineralogy of reef-building and sediment-producing organisms is thus regulated by chemical reactions occurring along the mid-ocean ridge, the rate of which is controlled by the rate of sea-floor spreading. The first indications that a ridge bisects the Atlantic Ocean basin came from the results of the British Challenger expedition in the nineteenth century. Soundings from lines dropped to

4900-485: Was previously not understood from the geological studies near Grande Terre and Northland which fitted best an induced subduction initiation model. The Norfolk Ridge basement is 20–25 km (12–16 mi) thick with continental crust characteristics. It can be seen as a continuation of the mesozoic basement of Grande Terre (Tremena and Central Chain terranes ) through to the Waipapa and Murihiku terranes of New Zealand. There

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