A WWII submarine-hunting gadget helped show plate tectonics

That is the story of how the world travels of a 19th century explorer, two bar magnets and the World Struggle II hunt for enemy submarines led to the invention of the transportable fluxgate magnetometer. And the way that invention, in flip, led to the “magic profile,” a strong piece of proof for the idea of plate tectonics.

Within the 1950s, the concept Earth’s continents is perhaps on the transfer was largely ridiculed, and the seafloor was nonetheless principally a thriller. However that was about to vary: Within the aftermath of World Struggle II and its naval battles, researchers out of the blue had highly effective new instruments, corresponding to submersibles and sonar methods, to map and probe the seafloor in higher element than ever earlier than. Amongst these new applied sciences was a small, transportable gadget often known as a fluxgate magnetometer.

Magnetometers, units that measure Earth’s magnetic subject, have been removed from a brand new know-how at that time. Scientists had identified for hundreds of years that Earth produces its personal magnetic subject; sailors used compasses to navigate by it. However the power of that subject was puzzlingly inconsistent from place to put.

Throughout his travels across the globe within the early 1800s, the German explorer and geographer Alexander von Humboldt collected measurements of Earth’s magnetic subject at totally different areas, noting that the sphere’s depth elevated farther from the equator. These variations led Humboldt in 1831 to provoke a coordinated effort to exactly measure this magnetic depth all over the world. Amongst others, he enlisted the assistance of German mathematician Carl Friedrich Gauss on this effort.

Gauss delivered. In 1833, he reported devising the primary magnetometer, which might measure absolutely the depth of Earth’s magnetic subject at any location. His magnetometer was deceptively easy, consisting of two bar magnets, one suspended within the air by a fiber and one positioned a identified distance away. The deflection of the suspended magnet from geomagnetic north is dependent upon each the depth of Earth’s magnetic subject and the pull of the second bar magnet. These measurements succeeded in offering the primary international maps of Earth’s magnetic subject power.

However by World Struggle II, the U.S. Navy was on the lookout for much more exact measurements of magnetism. Particularly, the Navy needed to have the ability to map very small anomalies in Earth’s magnetic subject — anomalies that is perhaps due, for instance, to the presence of metallic objects, corresponding to submarines, beneath the floor of the water.

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In 1836, scientists designed such a exact sensor, referred to as a fluxgate magnetometer. In a fluxgate magnetometer, as a substitute of a spinning needle like in a compass, a bar of iron is wrapped in two coils of wire. One coil carries an alternating present alongside the size of the iron core, tinkering with the core’s magnetic state, first saturating it with magnetism after which desaturating it. When within the unsaturated state, the core can pull in an exterior magnetic subject, corresponding to Earth’s. When saturated, the core pushes the exterior subject again out. The second coil is there to detect these adjustments in magnetism — and alongside the best way can very exactly measure the power of the exterior subject.

However to make use of this gadget to search for submarines, it must be transportable, capable of be mounted on an airplane. That’s the place Russian-born geomagnetist Victor Vacquier enters the story. Vacquier was on the Pittsburgh-based Gulf Analysis Laboratories, an arm of Gulf Oil, the place, for a number of years, he had been arduous at work on a transportable model of the fluxgate magnetometer.

In 1941, profitable assessments of Vacquier’s gadget drew the eye of the Navy, which noticed the protection potential of his gadget. With naval funding, fluxgate magnetometers have been airborne by December 1942 and busily trying to find enemy submarines.

After the warfare, scientists have been desperate to see what this exact, transportable magnetometer might reveal in regards to the seafloor. Oceanographers refitted the gadget so it could possibly be towed behind analysis vessels as they swept backwards and forwards throughout the oceans. In the course of the 1950s and early 1960s, Vacquier (by then at Scripps Establishment of Oceanography in La Jolla, Calif.) and different researchers started utilizing the fluxgate magnetometer to measure and map magnetic anomalies preserved within the seafloor rocks.

This zebra-stripe sample, from information collected in 1966 from the Reykjanes Ridge southwest of Iceland, exhibits symmetry within the magnetic orientations of seafloor rocks on both aspect of the central ridge (oriented higher proper to decrease left).F.J. Vine, Science 1966

The maps revealed a curious zebra-stripe sample of magnetic polarity on the seafloor, one thing by no means seen in continental rocks. On this sample, bands of rocks with regular polarity — the north-south orientation comparable to that of Earth’s present magnetic subject — alternated with bands of reversed polarity. These stripes, scientists hypothesized, is perhaps as a consequence of Earth’s magnetic subject reversing course every now and then.

Much more tellingly, the zebra-stripe sample turned out to be symmetrical on both aspect of the lengthy, snaking underwater mountain chains often known as mid-ocean ridges. That sample turned one of the highly effective traces of proof for the speculation of seafloor spreading, the concept as Earth’s crust pulls aside on the mid-ocean ridges, magma wells as much as kind new ocean crust. As the brand new crust hardens, its iron-bearing minerals align with the present orientation of Earth’s magnetic subject, and the hardening rocks develop into a brand new stripe within the sample.  

In 1968, about 100 earth scientists met for what was about to develop into a seminal second within the story of plate tectonics. On the assembly, a two-day symposium held on the Goddard Institute for House Research in New York Metropolis, geologists Walter Pitman and James Heirtzler of Lamont-Doherty Earth Observatory in Palisades, N.Y., offered a profile of magnetic anomalies they’d measured in 1966 from aboard the R/V Eltanin.

In 1965, scientists aboard the R/V Eltanin traversed the Pacific-Antarctic Ridge towing a magnetometer. One traverse, referred to as Eltanin-19 (proven), revealed such exceptional symmetry within the magnetic orientation of seafloor rocks that it got here to be referred to as the “magic profile.” The sample from west to east (prime line) practically matches the sample from east to west (center line) — revealing the symmetry. The underside line exhibits expectations from a pc simulation.W.C. Pitman III, J.R. Heirtzler, Science 1966

The symmetry on both aspect of the Pacific-Antarctic Ridge was crystal clear, so excellent that it turned often known as the “magic profile.” This profile, made doable by a sequence of innovations over the earlier century that culminated in a transportable, exact magnetometer, turned one of the convincing traces of proof for seafloor spreading — and in the end, for the idea of plate tectonics.

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