Richard Rayman Doell and Brent Dalrymple’s discovery of the magnetic reversals of Earth’s poles represented a breakthrough in understanding the history of the planet and a major missing piece of the theory of continental drift.

In the early twentieth century, the idea was proposed that the polarity of the earth’s magnetic field experienced changes. This was based on studies by geophysicists of remanent magnetization of volcanic rocks and baked earth. In 1906, Bernard Brunhes Brunhes, Bernard , a French physicist, found volcanic rocks magnetized in the opposite direction with reference to the earth’s present magnetic field. He concluded that the magnetic field had reversed. His conclusion was accepted, but scientists were not interested in this type of research at that time. Continental drift
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Magnetic field of Earth
“Recent Developments in the Geomagnetic Polarity Epoch Time-Scale” (Dalrymple, Doell, and Cox)[Recent Developments in the Geomagnetic Polarity Epoch Time Scale]
[kw]Doell and Dalrymple Discover the Magnetic Reversals of Earth’s Poles (Nov. 4, 1965)
[kw]Dalrymple Discover the Magnetic Reversals of Earth’s Poles, Doell and (Nov. 4, 1965)
[kw]Magnetic Reversals of Earth’s Poles, Doell and Dalrymple Discover the (Nov. 4, 1965)
[kw]Earth’s Poles, Doell and Dalrymple Discover the Magnetic Reversals of (Nov. 4, 1965)
Continental drift
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Magnetic field of Earth
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[g]North America;Nov. 4, 1965: Doell and Dalrymple Discover the Magnetic Reversals of Earth’s Poles[08650]
[g]United States;Nov. 4, 1965: Doell and Dalrymple Discover the Magnetic Reversals of Earth’s Poles[08650]
[c]Earth science;Nov. 4, 1965: Doell and Dalrymple Discover the Magnetic Reversals of Earth’s Poles[08650]
[c]Science and technology;Nov. 4, 1965: Doell and Dalrymple Discover the Magnetic Reversals of Earth’s Poles[08650]
Doell, Richard Rayman
Dalrymple, Brent
Cox, Allan V.

Laboratory studies showed that volcanic rocks and baked earth, when heated to their Curie temperature (the temperature above which a substance is no longer magnetic) and allowed to cool, acquired a weak and stable remanent magnetization (thermoremanent magnetism develops in igneous rocks when they cool below the Curie temperature), which was paralleled to the earth’s present magnetic field. Scientists also found bricks and baked earth in archaeological sites that had their magnetism reversed because of fires made by humans. Lava flows also change the magnetism of rocks (referred to as baked earth) that they have covered.

In 1925, R. Chevallier Chevallier, R. studied lava flows from Mount Etna, which contained remanent magnetizations that correlated with the magnetic field of the earth at the time of their eruption. In 1926, Paul L. Mercanton Mercanton, Paul L. suggested that if magnetized rocks showed a reversed magnetic field for the earth, then those reversals should be recorded worldwide in other rocks. Motonori Matuyama Matuyama, Motonori , in 1929, was the first paleomagnetist to determine the times when the magnetic field had reversed itself by determining the ages of rocks. He found that the youngest rocks with reversed polarity were of early Quaternary period. After this early work on geomagnetic reversals, little was done in this area from 1928 to 1948. This resulted from the fact that science did not have an adequate theory to explain the earth’s magnetic field, much less magnetic reversals. The study of magnetic reversals resumed around 1950. This resulted from the theory of how the earth’s magnetic field was produced. The mechanism proposed was that of a magnetohydrodynamic dynamo.

The theory developed from the work of Walter M. Elsasser Elsasser, Walter M. and Sir Edward Bullard Bullard, Edward . The dynamo idea suggested that Earth’s outer core consisted of molten iron and nickel and was similar to the electrical conductors of a dynamo. It was hypothesized that the rotation of the earth produced convection currents in the outer core and that the resulting electric currents created an eternal magnetic field in the earth. The magnetic lines of force that would develop would be similar to those formed as if there was a bar magnet inside the earth. This, however, did not explain how the earth’s magnetic field could reverse itself.

Scientists have suggested that a period of strong solar-flare activity could cause the magnetic field to die and that after this activity was over the magnetic field would come back, but in a reversed manner. The question has arisen as to whether the magnetism in a rock can go through self-reversal. Laboratory experiments show that this occurs in less than 1 percent of thousands of rock samples tested from around the world. Therefore, if reversal of the magnetic field is the correct explanation for geomagnetic reversals, transitions from reversed to normal polarization, or the opposite, must occur at the same stratigraphic horizon worldwide.

Many geologists and geophysicists have done work in paleomagnetism, but the work of Richard Rayman Doell and Brent Dalrymple provided a complete picture of paleomagnetic reversals of the past 5 million years. Allan V. Cox, Doell, and Dalrymple spent five years (1959-1964) working on continental volcanic rocks from Alaska, Hawaii, Idaho, California, and New Mexico, to determine if the last magnetic reversal from reversed polarity (named the Matuyama reversed epoch) to the present normal polarity (named the Brunhes normal epoch) occurred contemporaneously around the world approximately 1 million years ago. Paleomagnetists had up to this time not found magnetic reversals in the upper Pleistocene.

Geologically, 1 million years ago marks the transition from the Pleistocene epoch (the last Ice Age) to the Holocene (or recent) epoch of time. (Some geologists refer to the Holocene as the upper Pleistocene.) Reversals first appeared in the recent geologic record in the middle and lower Pleistocene (1 million to 2 million years ago). By 1964, Cox, Doell, and Dalrymple had found no evidence for contemporaneous reversals to conform the change from the Matuyama reversed epoch to the Brunhes normal epoch. This problem eluded them for another year.

Earth’s magnetic field has gone through several polarity reversals over the planet’s history.

In 1965, while Cox was doing research abroad, Doell and Dalrymple continued their study of volcanic rocks from the Valles Caldera in New Mexico, which is part of the Jemez Mountains located 56 kilometers northwest of Santa Fe. On November 4, 1965, at a meeting of the Geological Society of America in Kansas City, Missouri, Dalrymple presented a paper, written by himself, Doell, and Cox, in which preliminary results from their work in New Mexico were reported. The paper was entitled “Recent Developments in the Geomagnetic Polarity Epoch Time-Scale,” and it contained the following statement: “There may be another event at about 0.9 million years, although it is yet not confirmed. Because of the short duration of these events, the chances of finding another one are rather small; thus subsequent work may turn up additional events that are as yet unrecognized.”

On May 20, 1966, Science published a two-page article by Doell and Dalrymple, “Geomagnetic Polarity Epochs: A New Polarity Event and the Age of the Brunhes-Matuyama Boundary.” “Geomagnetic Polarity Epochs” (Doell and Dalrymple)[Geomagnetic Polarity Epochs] Doell and Dalrymple determined the radiometric age using the potassium-argon method and paleomagnetism of nineteen Pleistocene volcanic rock units collected during the summer of 1964 in the Valles Caldera. Six samples had ages that ranged from 0.7 to 1.0 million years. These dates coincided with the age of the Bishop Tuff of California, which had been dated at between 0.87 and 1.2 million years.

The new dates were valuable in defining the Matuyama-Brunhes boundary, which was established at 0.7 million years. Their study of the rock samples from New Mexico showed that a magnetic field reversal took place between 0.8 and 0.9 million years ago. This event occurred toward the end of the Matuyama reversed polarity epoch. These rocks showed a normal polarity, and the event has been named the Jaramillo normal event Jaramillo normal event after a creek in the area where the rocks had been collected. The rocks dated between 0.7 and 0.8 million years ago showed a reversed polarity. From 0.7 million years ago to the present, the rocks from New Mexico indicated a normal polarity. The type of brief reversals, as the Jaramillo normal event, occurred earlier in the Matuyama reversed epoch and is known as the Olduvai normal event, which lasted 0.32 million years. During the Gauss normal epoch, which precedes the Matuyama reversed epoch, a brief reversal event called the Mammoth reversed event occurred, which lasted 0.12 million years.

In 1963, Fred J. Vine Vine, Fred J. , Drummond H. Matthews Matthews, Drummond H. , and Lawrence W. Morley Morley, Lawrence W. independently proposed the hypothesis that the rock of the ocean floor showed evidence of magnetic field reversals. These magnetic stripes mirrored each other on opposite sides of midoceanic ridges and were of the same thickness. In February, 1966, the new geomagnetic polarity-reversal time scale that contained the Jaramillo event developed by Doell and Dalrymple was correlated with the magnetic-anomaly profiles across midoceanic ridges. The Vine-Matthews-Morley hypothesis (better known as the Vine-Matthews hypothesis) was confirmed and the theory of seafloor spreading and continental drift became inevitable.

About the same time, from a third source of independently derived data, polarity reversals were demonstrated in deep-sea sediment cores. In February, 1966, while Vine visited Neil Opdyke Opdyke, Neil at the Lamont-Doherty Geological Observatory, Opdyke mentioned to Vine that he and his colleagues had discovered a new magnetic anomaly at about 0.9 million years in deep-sea sediment cores from the South Pacific’s East Pacific Rise. These scientists had found the same magnetic reversal as Doell and Dalrymple had found on land. Other oceanic cores from various parts of the world also showed the reversal. This confirmed further that the Jaramillo event was a worldwide event.

At one time the question was asked if the poles had wandered (known as polar wandering) throughout geologic time or if the continents had drifted. Paleomagnetism has proved that the magnetic field, despite its reversals, shows having had a common North Pole. Studies of rocks of various geologic ages from North America and Europe have been correlated and show that the paleomagnetism preserved in the rocks points toward a common North Pole. When Europe and North America are rotated back together to a predrift position, the apparent polar wandering curves of both continents come together and point toward a common North Pole.

Paleomagnetism was the keystone piece of the continental drift puzzle. It also added credence to the plate tectonics theory, formally called the continental drift theory. Other scientific data that had been collected and studied also helped confirm the idea of seafloor spreading. A revolution in the earth sciences had been triggered by the work of Doell and Dalrymple. Continental drift
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Magnetic field of Earth
“Recent Developments in the Geomagnetic Polarity Epoch Time-Scale” (Dalrymple, Doell, and Cox)[Recent Developments in the Geomagnetic Polarity Epoch Time Scale]

• 
  Continents Adrift: Readings from “Scientific American.” San Francisco: W. H. Freeman, 1972. Introductions by J. Tuzo Wilson. Includes fourteen articles from Scientific American, in chronological order, written for the general reader. Traces the history of a scientific revolution in the earth sciences. The articles contain many maps, graphs, photographs, charts, and illustrations. A valuable resource for the student of the earth sciences.
• Cox, Allan, ed. Plate Tectonics and Geomagnetic Reversals. San Francisco: W. H. Freeman, 1973. A collection of articles on research in plate tectonic and geomagnetic reversals selected, edited, and with introductions by Cox. Articles are in chronological order so the reader can follow the events as they unfold. Includes technical but easily understood articles. A valuable resource for the earth science student. Many illustrations and references.
• Cox, Allan, G. Brent Dalrymple, and Richard R. Doell. “Reversals of the Earth’s Magnetic Field.” Scientific American 216 (February, 1967): 44-54. An easy-to-read article on the events leading up to the discovery of the Jaramillo event. It reviews the early work done on the reversals of the earth’s magnetic field. A valuable resource for the student of the earth sciences. Includes illustrations and a chronology of the earth’s magnetic field for the last 4 million years.
• Glen, William. The Road to Jaramillo: Critical Years of the Revolution in Earth Science. Stanford, Calif.: Stanford University Press, 1982. The layperson’s version of Plate Tectonics and Geomagnetic Reversals. The story of a cast of international scientists that produced discoveries in the area of plate tectonics that brought about a revolution in the earth sciences. Includes photographs of scientists and illustrations to explain the concepts being introduced.
• McElhinny, Michael W., and Phillip L. McFadden. Paleomagnetism: Continents and Oceans. San Diego, Calif.: Academic, 2000. Textbook on paleomagnetism, its study, and its significance. Includes a chapter on magnetic field reversals. Bibliographic references and index.
• Menard, H. W. The Ocean of Truth: A Personal History of Global Tectonics. Princeton, N.J.: Princeton University Press, 1986. An insider’s account by a geologist who was involved with the findings that led to plate tectonics. He examines the controversial history of global tectonics from 1900 to 1968. A valuable resource for the student of the earth sciences. It includes photographs of scientists, drawings, and maps.
• Vrielynck, Bruno, and Philippe Bouysse. The Changing Face of the Earth: The Break-Up of Pangaea and Continental Drift over the Past 250 Million Years in Ten Steps. Paris: UNESCO, 2003. Booklet of maps showing the evolution of the Earth’s surface over 250 million years. Invaluable for understanding the effects of continental drift.

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