Mid-Atlantic Ridge (MAR)

The Mid-Atlantic Ridge is a mid-ocean ridge system found in the Atlantic Ocean that makes up the longest mountain range in the world. A mid-ocean ridge is an underwater mountain range formed by plate tectonics, which are processes that affect the structure of Earth's crust. The uplifting of the ocean floor to create the ridges occurs when convection currents rise in the mantle beneath the oceanic crust and create magma where two tectonic plates meet at a divergent boundary. The Mid-Atlantic Ridge is part of the global mid-ocean ridge system and is made up of a divergent plate boundary where continental plates are moving apart, creating the ridge. In the northern part of the ridge, the Eurasian Plate is moving eastward, and the North American Plate is moving westward. The boundary between the two creates the Mid-Atlantic Ridge. In the southern portion of the ridge, it separates the African Plate and the South American Plate. The entire Mid-Atlantic Ridge is approximately ten thousand miles long, running from a point about two hundred miles south of the North Pole to the sub-Antarctic Bouvet Island.

Background

Early in 1850, American oceanographer Matthew Fontaine Maury first speculated that an underwater mountain range existed in the Atlantic Ocean. It was not until 1872, however, that the existence of the Mid-Atlantic Ridge was confirmed during the expedition of the HMS Challenger. Crew members, which included three scientists, were investigating the Atlantic Ocean for the purpose of laying the transatlantic telegraph cable when they discovered a large rise in the middle of the ocean floor. By 1925, the existence of the ridge was further confirmed with the invention of sonar. This new technology, which uses sound to detect objects on or under the surface of the water, allowed scientists to map the Mid-Atlantic Ridge.

Thanks to sonar, scientists discovered that the Mid-Atlantic Ridge had a central valley spanning its entire length where many earthquakes occurred. This led to the wider acceptance in the scientific community of Alfred Wegener's theory of continental drift. The German researcher had theorized in 1912 that the continents were slowly drifting around Earth. Wegener's theory became known as the theory of plate tectonics, which states that the outer rigid layer of Earth is divided into dozens of plates that move across the surface of the Earth relative to one another.

By the 1960s, scientists were able to complete maps of Earth's ocean floors. This mapping revealed a seismically active central valley to the Mid-Atlantic Ridge, in addition to a network of valleys and ridges. Scientists also discovered that the ridge was part of a continuous system of mid-ocean ridges that extended across the entire ocean floor, connecting all the divergent boundaries across the world.

Overview

The Mid-Atlantic Ridge has formed as a result of the divergent movement between the Eurasian and North American Plates and the African and South American Plates. As the mantle rises toward the surface below the ridge, the pressure drops, and the hot rock begins to partially melt. This produces basaltic volcanoes when an eruption occurs above the surface of the water and characteristic basalt, or "pillow lava," when an eruption occurs underwater. As the plates move further apart, new ocean floor is formed at the ridge, and the ocean basin gets wider. This process is known as seafloor spreading, which is when new oceanic crust is formed through volcanic activity on a mid-ocean ridge.

Part of the longest mountain chain in the world, the Mid-Atlantic ridge extends continuously across the ocean floor for a total distance of about twenty-five thousand miles. It has a deep rift valley at its crest, which marks the location where the two plates are moving apart. This rift valley, measuring 50 to 75 miles wide, runs along the axis of the ridge for nearly its entire length and marks the boundary between adjacent tectonic plates. The rift valley is also where magma from the mantle reaches the seafloor. The peaks of the Mid-Atlantic Ridge rise about two miles in height, reaching above sea level in spots and forming a set of volcanic islands of varying sizes that run the length of the Atlantic Ocean.

One island formed by the volcanic activity along the Mid-Atlantic Ridge is the nation of Iceland, which lies on the northern part of the ridge. On Iceland's western side is part of the North American Plate, and on its eastern side lies the Eurasian Plate. The Thingvellir Rift Valley of Iceland, where the plates are separating, is about ten thousand years old. The rift valley has widened about 230 feet and sunk about 131 feet during that time. Volcanoes have erupted over the years, creating new land on the island as the plates drift apart. Other islands formed by the Mid-Atlantic Ridge—and the nations that own them—include the following:

• Jan Mayen (Norway)
• Azores (Portugal)
• St. Paul's Rock (Brazil)
• Ascension Island (United Kingdom)
• St. Helena (United Kingdom)
• Tristan da Cunha (United Kingdom)
• Gough Island (United Kingdom)
• Bouvet Island (Norway)

The discovery and further mapping of the Mid-Atlantic Ridge led to new theories in geology and planetary evolution and helped scientists further understand the world, how it was formed, and how it continues to change. In addition to the wider acceptance of Wegener's theories of continental drift and plate tectonics, the theory of seafloor spreading was attributed to the discovery of the Mid-Atlantic Ridge. In addition, the discovery led to the theory that all the continents on Earth were once part of a single landmass known as Pangaea, which broke apart approximately 180 million years ago.

Bibliography

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