scientist who developed the seafloor spreading hypothesis

If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

To log in and use all the features of Khan Academy, please enable JavaScript in your browser.

Big History Project

Course: big history project   >   unit 4.

• ACTIVITY: DQ Notebook 4.3
• WATCH: Introduction to Geology

READ: Alfred Wegener and Harry Hess

• ACTIVITY: Claim Testing – Geology and the Earth’s Formation
• READ: A Girl Talk Geological Revolution - Marie Tharp: Graphic Biography
• READ: Eratosthenes of Cyrene
• WATCH: Introduction to the Geologic Time Chart
• READ: Principles of Geology
• ACTIVITY: What Do You Know? What Do You Ask?
• READ: The Universe Through a Pinhole — Hasan Ibn al-Haytham
• READ: Gallery — Geology
• Quiz: Our Solar System and Earth

A Meteorologist, a Geologist, and the Theory of Plate Tectonics

Balloons and arctic air, continental drift, seafloor spreading, plate tectonics, for further discussion, want to join the conversation.

• Upvote Button navigates to signup page
• Downvote Button navigates to signup page
• Flag Button navigates to signup page

ENCYCLOPEDIC ENTRY

Seafloor spreading.

Seafloor spreading is a geologic process in which tectonic plates—large slabs of Earth's lithosphere—split apart from each other.

Earth Science, Geology, Meteorology, Geography, Physical Geography

Loading ...

Seafloor spreading is a geologic process in which tectonic plates —large slabs of Earth's lithosphere —split apart from each other. Seafloor spreading and other tectonic activity  processes are the result of mantle convection . Mantle convection is the slow, churning motion of Earth’s mantle . Convection currents carry heat from the lower mantle and core to the lithosphere . Convection currents also “recycle” lithospheric materials back to the mantle .

Seafloor spreading occurs at divergent plate boundaries. As tectonic plates slowly move away from each other, heat from the mantle’s convection currents makes the crust more plastic and less dense . The less-dense material rises, often forming a mountain or elevated area of the seafloor. Eventually, the crust cracks. Hot magma fueled by mantle convection bubbles up 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 mountain 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 East 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 boundary 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 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 center . It spreads about 6-16 centimeters (3-6 inches) every year. There is not an ocean trench at the East Pacific Rise, because the seafloor spreading is too rapid for one to develop!

The newest, thinnest crust on Earth is located near the center of mid-ocean ridges—the actual site of seafloor spreading. The age, density, and thickness of oceanic crust 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 fairly magnetic substance, and scientists began using magnetometers to measure the magnetism of the ocean floor 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 rock is determined by the Earth’s magnetic field when the magma is cooling. Scientists determined that the same process formed the perfectly symmetrical stripes on both side of a mid-ocean ridge. The continual process of seafloor spreading separated the stripes in an orderly pattern.

Geographic Features

Oceanic crust slowly moves away from mid-ocean ridges and sites of seafloor spreading. As it moves, it becomes cooler, more dense, and more thick. Eventually, older oceanic crust encounters a tectonic boundary with continental crust . In some cases, oceanic crust encounters an active plate margin . An active plate margin is an actual plate boundary, where oceanic crust and continental crust crash into each other. Active plate margins are often the site of earthquakes and volcanoes . Oceanic crust created by seafloor spreading in the East Pacific Rise, for instance, may become part of the Ring of Fire , the horseshoe-shaped pattern of volcanoes and earthquake zones around the Pacific ocean basin .

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 crust of a passive margin. The oceanic crust of the Mid-Atlantic Ridge, for instance, will either become part of the passive margin on the North American plate (on the east coast of North America) or the Eurasian plate (on the west coast of Europe).

New geographic features can be created through seafloor spreading. The Red Sea, for example, was created as the African plate and the Arabian plate tore away from each other. Today, only the Sinai Peninsula connects the Middle East (Asia) with North Africa. Eventually, geologists predict , seafloor spreading will completely separate the two continents—and join the Red and Mediterranean Seas.

Mid-ocean ridges and seafloor spreading can also influence sea levels . As oceanic crust moves away from the shallow mid-ocean ridges, it cools and sinks as it becomes more dense. This increases the volume of the ocean basin and decreases the sea level. For instance, a mid-ocean ridge system in Panthalassa—an ancient ocean that surrounded the supercontinent Pangaea —contributed to shallower oceans and higher sea levels in the Paleozoic era . Panthalassa was an early form of the Pacific Ocean, which today experiences less seafloor spreading and has a much less extensive mid-ocean ridge system. This helps explain why sea levels have fallen dramatically over the past 80 million 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 just one part of plate tectonics . Subduction is another. Subduction happens where tectonic plates crash into each other instead of spreading apart. At subduction zones, the edge 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 old crust. The two forces roughly balance each other, so the shape and diameter of the Earth remain constant.

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 central point where three cracks (boundaries) split 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 Great Rift Valley and Red Sea (a major site of seafloor spreading) are the result of plate tectonics in the Afar Triple Junction.

Media Credits

The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit. The Rights Holder for media is the person or group credited.

Last Updated

November 29, 2023

User Permissions

For information on user permissions, please read our Terms of Service. If you have questions about how to cite anything on our website in your project or classroom presentation, please contact your teacher. They will best know the preferred format. When you reach out to them, you will need the page title, URL, and the date you accessed the resource.

If a media asset is downloadable, a download button appears in the corner of the media viewer. If no button appears, you cannot download or save the media.

Text on this page is printable and can be used according to our Terms of Service .

Interactives

Any interactives on this page can only be played while you are visiting our website. You cannot download interactives.

Related Resources

• school Campus Bookshelves
• menu_book Bookshelves
• perm_media Learning Objects
• login Login
• how_to_reg Request Instructor Account
• hub Instructor Commons

Margin Size

• Download Page (PDF)
• Download Full Book (PDF)
• Periodic Table
• Physics Constants
• Scientific Calculator
• Reference & Cite
• Tools expand_more
• Readability

selected template will load here

This action is not available.

5.6: Seafloor Spreading Hypothesis

• Last updated
• Save as PDF
• Page ID 5384

\( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \)

\( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)

\( \newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\)

( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\)

\( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\)

\( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\)

\( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\)

\( \newcommand{\Span}{\mathrm{span}}\)

\( \newcommand{\id}{\mathrm{id}}\)

\( \newcommand{\kernel}{\mathrm{null}\,}\)

\( \newcommand{\range}{\mathrm{range}\,}\)

\( \newcommand{\RealPart}{\mathrm{Re}}\)

\( \newcommand{\ImaginaryPart}{\mathrm{Im}}\)

\( \newcommand{\Argument}{\mathrm{Arg}}\)

\( \newcommand{\norm}[1]{\| #1 \|}\)

\( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\AA}{\unicode[.8,0]{x212B}}\)

\( \newcommand{\vectorA}[1]{\vec{#1}}      % arrow\)

\( \newcommand{\vectorAt}[1]{\vec{\text{#1}}}      % arrow\)

\( \newcommand{\vectorB}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \)

\( \newcommand{\vectorC}[1]{\textbf{#1}} \)

\( \newcommand{\vectorD}[1]{\overrightarrow{#1}} \)

\( \newcommand{\vectorDt}[1]{\overrightarrow{\text{#1}}} \)

\( \newcommand{\vectE}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash{\mathbf {#1}}}} \)

How do the continents move?

Harry Hess was a geology professor and a naval officer. He commanded an attack transport ship during WWII. Hess was intrigued by the seafloor maps produced with the ship's echo sounder. He thought about all of the evidence for continental drift. He thought about all of the unusual features of the seafloor. And he found the mechanism to explain them all.

The Evidence Comes Together

World War II allowed scientists to make some puzzling observations. The observations came from seafloor bathymetry and magnetism. These observations are:

• The seafloor of the Atlantic Ocean has a large mountain range running through it. Deep trenches are found far from the ridges. Guyots have eroded tops that are deep below sea level.
• The magnetic polarity of the seafloor changes. The center of the ridge is of normal polarity. Stripes of normal and reverse polarity are found symmetrical on both sides of the ridge.
• The youngest seafloor is at the ridge. The oldest is farthest from the ridge. The oldest seafloor is much younger than the oldest continent.

Scientists needed to explain these observations.

Mantle Convection

Not long after Wegener's death, scientists recognized that there is convection in the mantle. Deeper material is hotter and so it rises. Near the surface, it becomes cooler and denser so it sinks. This creates a convection cell in the mantle.

Seafloor Spreading

After the war, Harry Hess put together the ideas and evidence he needed. Hess resurrected Wegener's continental drift hypothesis. He reviewed the mantle convection idea. He thought about the bathymetric features and the patterns of magnetic polarity on the seafloor. In 1962, Hess published a new idea that he called seafloor spreading .

Hess wrote that hot magma rises up into the rift valley at the mid-ocean ridges. The lava cools to form new seafloor. Later more lava erupts at the ridge. The new lava pushes the seafloor horizontally away from the ridge axis ( Figure below). The seafloor moves!

Magnetite crystals in the lava point in the direction of the magnetic north pole. The different stripes of magnetic polarity reveal the different ages of the seafloor.

In some places, the oceanic crust comes up to a continent. The moving crust pushes that continent away from the ridge axis as well. If the moving oceanic crust reaches a deep sea trench, the crust sinks into the mantle. The creation and destruction of oceanic crust is the reason that continents move.

Magma at the mid-ocean ridge creates new seafloor.

• As oceanic crust moves away from the ridge crest, it pushes a continent away from the ridge axis.
• If the oceanic crust reaches a deep sea trench, it sinks into the trench.
• The oldest crust is coldest and lies deepest in the ocean.

The flat topped guyots were once active volcanoes that were above sea level. They were eroded at their tops. As the seafloor moved away from the ridge, the crust sank deeper. The tops of the guyots went below sea level.

The Mechanism for Continental Drift

Seafloor spreading is the mechanism that Wegener was looking for! Convection currents within the mantle drive the continents. The continents are pushed by oceanic crust, like they are on a conveyor belt. Over millions of years the continents move around the planet’s surface. The spreading plate takes along any continent that rides on it.

• Seafloor spreading is a mixture different ideas and data. Continental drift and mantle convection are supported by bathymetric and magnetic data from the seafloor.
• Harry Hess called his idea “an essay in geopoetry." This could be because so many ideas fit together so well. It could also be because, at the time, he didn’t have all the seafloor data he needed for evidence.
• Seafloor spreading is the mechanism for the drifting continents.
• How does the pattern of magnetic stripes give evidence for seafloor spreading?
• How does the topography of the seafloor give evidence for seafloor spreading?
• How does seafloor spreading fit into the idea that continents move about on Earth’s surface?

Plate Tectonics

Seafloor spreading, lesson objectives.

• Describe the main features of the seafloor.
• Explain what seafloor magnetism tells scientists about the seafloor.
• Describe the process of seafloor spreading.
• abyssal plains
• echo sounder
• seafloor spreading

Introduction

World War II gave scientists the tools to find the mechanism for continental drift that had eluded Wegener. Maps and other data gathered during the war allowed scientists to develop the seafloor spreading hypothesis. This hypothesis traces oceanic crust from its origin at a mid-ocean ridge to its destruction at a deep sea trench and is the mechanism for continental drift.

Seafloor Bathymetry

During World War II, battleships and submarines carried echo sounders to locate enemy submarines ( Figure below ). Echo sounders produce sound waves that travel outward in all directions, bounce off the nearest object, and then return to the ship. By knowing the speed of sound in seawater, scientists calculate the distance to the object based on the time it takes for the wave to make a round-trip. During the war, most of the sound waves ricocheted off the ocean bottom.

Lesson Summary

• Using technologies developed to fight World War II, scientists were able to gather data that allowed them to recognize seafloor spreading as the mechanism for Wegener’s drifting continents.
• Bathymetric maps revealed high mountain ranges and deep trenches in the seafloor.
• Magnetic polarity stripes give clues to seafloor ages and the importance of mid-ocean ridges in the creation of oceanic crust.
• Seafloor spreading processes create new oceanic crust at mid-ocean ridges and destroy older crust at deep sea trenches.

Review Questions

• Describe how sound waves are used to develop a map of the features of the seafloor.
• Why is the oldest seafloor less than 180 million years when the oldest continental crust is about 4 billion years old?
• Describe the major features and the relative ages of mid-ocean ridges, deep sea trenches, and abyssal plains.
• Describe how continents move across the ocean basins as if they are on a conveyor belt.
• If you were a paleontologist who studies fossils of very ancient life forms, where would be the best place to look for very old fossils: on land or in the oceans?
• Imagine that Earth’s magnetic field was fixed in place and the polarity didn’t reverse. What effect would this have on our observations of seafloor basalts?
• Look at a map of the Atlantic seafloor with magnetic polarity stripes and recreate the history of the Atlantic Ocean basin.

Further Reading / Supplemental Links

• A basic description of sea floor spreading with animations: http://www.pbs.org/wnet/savageearth/hellscrust/index.html .

Points to Consider

• How were the technologies that were developed to fight World War II used by scientists for the development of the seafloor spreading hypothesis?
• In what two ways did magnetic data lead scientists to understand more about continental drift and plate tectonics?
• How does seafloor spreading provide a mechanism for continental drift?
• Look at the features of the North Pacific Ocean basin and explain them in seafloor spreading terms.
• What would have to happen if oceanic crust was not destroyed at oceanic trenches, but new crust was still created at mid-ocean ridges?
• Earth Science for High School. Provided by : CK-12. Located at : http://www.ck12.org/book/CK-12-Earth-Science-For-High-School/ . License : CC BY-NC: Attribution-NonCommercial

• Plate Tectonics
• Teachers zone
• Test your knowledge
• How to use this site
• Acknowledgements
• Pioneers of Plate Tectonics
• Geological Fit
• Tectonic Fit
• Glacial Deposits
• Fossil Evidence

Harry Hammond Hess

• Frederick Vine and Drummond Matthews
• John Tuzo-Wilson
• Dan McKenzie

Harry Hess was a professor of geology at Princeton University (USA), and became interested in the geology of the oceans while serving in the US Navy in World War II. His time as a Navy officer was an opportunity to use sonar (also called echo sounding), then a new technology, to map the ocean floor across the North Pacific.

He published ‘ The History of Ocean Basins ' in 1962, in which he outlined a theory that could explain how the continents could actually drift. This theory later became known as ‘ Sea Floor Spreading '.

Hess discovered that the oceans were shallower in the middle and identified the presence of Mid Ocean Ridges , raised above the surrounding generally flat sea floor ( abyssal plain ) by as much as 1.5 km. In addition he found that the deepest parts of the oceans were very close to continental margins in the Pacific with Ocean Trenches extending down to depths of over 11 km in the case of the Marianas Trench off the coast of Japan.

Hess envisaged that oceans grew from their centres, with molten material (basalt) oozing up from the Earth’s mantle along the mid ocean ridges. This created new seafloor which then spread away from the ridge in both directions. The ocean ridge was thermally expanded and consequently higher than the ocean floor further away. As spreading continued, the older ocean floor cooled and subsided to the level of the abyssal plain which is approximately 4 km deep.

Hess believed that ocean trenches were the locations where ocean floor was destroyed and recycled.

Although his theory made sense, Hess knew, like Wegener, that he still needed convincing geophysical evidence to support it. This was to come just a year after his 1962 publication...

Next pioneer

• GSL Homepage
• Privacy Policy
• Terms & conditions

Continental Drift and Seafloor Spreading

The keys to modern earth and oceanographic sciences.

Until only recently, geologists had thought that Earth’s surface hadn’t changed much since the planet formed 4.6 billion years ago. They believed that the oceans and continents were always where they are now.

But less than 100 years ago, a German scientist named Alfred Wegener took notice of some interesting findings. Similar plant and animal fossils were found in both Africa and South America and on other continents separated by oceans. Similar rock formations were also found on distant continents. This suggested that the formations were once whole and later divided.

Wegener also noticed that if you could shove western Europe and Africa together with North and South America, their coastlines would fit together very neatly. All this evidence led Wegener to believe that the continents were once connected but had separated and drifted apart.

In 1915, Wegener proposed his continental drift theory. He said that the continents floated atop the mantle-a heavier, denser layer of rocks deep within the earth. Wegener predicted that heat rising within the hot mantle created currents of partially melted rocks that could move the continents around the earth’s surface.

Like many revolutionary theories, Wegener’s was not initially accepted by scientists. The “good fit” of the continents and the fossil and rock evidence did not provide enough proof. For decades afterward, scientists still did not understand how massive continents could be transported across the face of the Earth, and they had no evidence of any process that could cause continents to move.

In the 1950s and 1960s, marine geologists such as Bruce Heezen, Marie Tharp, and Henry Menard used data from echo sounders to map ocean ridges in the North Atlantic and the Pacific. They noticed first that these ridges stretched on for thousands of kilometers in long, continuous mountain chains that wound around the Earth’s surface, almost like the stitches on a baseball. The scientists also observed that the crest of the ridges had a topography that closely resembled volcanic rift zones on land. At their crests, they had V-shaped central valleys with steep faults on either side. This evidence led early marine geologists to deduce that the mid-ocean ridges were formed by seafloor volcanoes.

When these volcanoes erupted, they spewed out lava that cooled and solidified to become new seafloor. It was soon discovered that when this lava cooled, magnetic particles within it aligned with Earth’s magnetic field. After World War II, when magnetometers began to be used to survey the seafloor’s magnetic properties, scientists were surprised to learn that Earth’s magnetic field had flip-flopped many times over its history, with the north and south poles exchanging places! So depending on when seafloor rocks were formed, their particles are aligned in either one direction or the other, and they are said to have either positive or negative magnetic anomalies.

In the late 1960s, magnetometer data revealed an alternating “striped” pattern of seafloor rocks. Rocks that formed when Earth’s magnetic field was in one position alternated with rocks that formed when the field was reversed. The stripes ran parallel to the mid-ocean ridges and extended out hundreds of miles on either side of them. The seafloor’s permanent magnetic signatures showed that new ocean crust was created at the ridge crests and then spread outward in both directions.

This seafloor spreading hypothesis had been proposed a few years earlier by Harry Hess, a petrologist at Princeton University, and Robert Dietz, an oceanographer in the US Coast and Geodetic Survey (the federal department that made maps of the oceans and US coastlines). Hess went on to say that as the ocean crust spreads and cools over millions of years, it becomes denser and eventually sinks down into oceanic trenches, or subduction zones, a long way from where it forms at the mid-ocean ridge crest. As ocean crust descends toward the hot mantle, it melts and becomes recycled into the mantle.

Volcanoes and earthquakes are common in subduction zones, which often occur at the edges, or margins, of continents. The Rim of Fire, which is named for its volcanoes and earthquakes, is created by a series of subduction zones along the coastlines surrounding the Pacific Ocean-from western South and Central America to the Aleutian Islands in Alaska, down the western Pacific, from Japan and the Philippines, all the way to Indonesia and New Zealand.

In 1965, a Canadian geophysicist, J. Tuzo Wilson, combined the continental drift and seafloor spreading hypotheses to propose the theory of plate tectonics. Tuzo said that Earth’s crust, or lithosphere, was divided into large, rigid pieces called plates. These plates “float” atop an underlying rock layer called the asthenosphere. In the asthenosphere, rocks are under such tremendous heat and pressure that they behave like a viscous liquid (like very thick honey). The term “continental drift” was no longer fully accurate, because the plates are made up of continental and oceanic crust, which both “drift” over Earth’s face.

Tuzo Wilson predicted three types of boundaries between plates: mid-ocean ridges (where ocean crust is created), trenches (where the ocean plates are subducted) and large fractures in the seafloor called transform faults, where the plates slip by each other. Plate tectonics has provided a unifying theory that explains the fundamental processes that shape the face of the Earth.

Hess’s Development of His Seafloor Spreading Hypothesis

Cite this chapter.

• Hank Frankel  

Part of the book series: Boston Studies in the Philosophy of Science ((BSPS,volume 60))

260 Accesses

4 Citations

In 1960 Harry Hess, in the words of Robert Fisher, “put it all together.” 1 What Hess put together was a mass of seemingly unrelated data when he proposed his seafloor spreading hypothesis. 2 This hypothesis had more to do with the eventual acceptance of continental drift theory in the form of plate tectonics by most researchers in the geosciences during the late sixties than any other conceptual innovation. The eventual acceptance of continental drift came with the confirmation of the Vine-Matthews hypothesis and J. T. Wilson’s transform fault hypothesis. Both of these hypotheses were virtual corollaries of Hess’s idea of seafloor spreading. 3 Hess grafted his hypothesis onto the existing continental drift tradition (hereafter DRIFT), and utilized his hypothesis as a plausible solution to the most serious problem faced by DRIFTers, namely, how on earth the continents could plow their way through the seafloor and remain intact. Consequently, Hess provided DRIFT with a new theory which solved the old empirical problems handled by DRIFT, offered a solution to their engineering problem by providing an adequate mechanism for the drift of the continents, and enabled DRIFT to take credit for solving new problems in oceanography and geophysics.

This is a preview of subscription content, log in via an institution to check access.

Access this chapter

• Available as PDF
• Read on any device
• Instant download
• Own it forever
• Durable hardcover edition
• Dispatched in 3 to 5 business days
• Free shipping worldwide - see info

Tax calculation will be finalised at checkout

Purchases are for personal use only

Institutional subscriptions

Unable to display preview.  Download preview PDF.

Bibliography

Betz, F., and Η. H. Hess: 1942, ‘The Floor of the North Pacific Ocean’, Geographical Review 32, 99–116.

Article   Google Scholar  

Fisher, R. L., and Η. H. Hess: 1963, ‘Trenches’, in M. N. Hill (ed.), The Sea, Vol. 3, John Wiley & Sons, New York, pp. 411–436.

Google Scholar  

Frankel, H.: 1979α, The Career of Continental Drift Theory: An Application of Imre Lakatos’ analysis of scientific growth to the rise of drift theory’, Studies in History and Philosophy of Science 10, 21–66.

Frankel, H.: 1979b, The Reception and Acceptance of Continental Drift Theory as a Rational Episode in the History of Science’, in S. H. Mauskopf (ed.), The Reception of Unconventional Science, American Assn. for the Advancement of Science, Washington, D. C., pp. 51–89.

Hess, Η. H.: 1932, “Interpretation of Gravity Anomalies and Sounding-profiles obtained in the West Indies by the International Expedition to the West Indies in 1932”, Transactions of the American Geophysical Union, 13th Annual Meeting, pp. 26–32.

Hess, Η. H.: 1937a, ‘Island Arcs, Gravity Anomalies, and Serpentine Intrusions: A contribution to the Ophiolite Problem’, 17th International Geological Congress, Moscow Report, Vol. 2, pp. 263–283.

Hess, Η. H.: 1937b, ‘Geological interpretation of data collected on cruise of U.S.S. Barracuda in the West Indies - preliminary report’, Transactions of the American Geophysical Union, 18th Annual Meeting, pp. 69–77.

Hess, H. Η.: 1938a ‘A Primary Peridotite Magma’, American Journal of Science 35, 322–344.

Hess, Η. H.: 1938b, ‘Gravity Anomalies and Island Arc Structure with Particular Refer-ence to the West Indies’, Proceedings of the American Philosophical Society 79, 71–96.

Hess, Η. H.: 1946, ‘Drowned Ancient Islands of the Pacific Basin’, American Journal of Science 244, 772 - 791.

Hess, Η. H.: 1951, ‘Comment on Mountain Building’, in 1950 Colloquium on Plastic Flow and Deformation within the Earth, Transactions of the American Geophysical Union 32, 528–531.

Hess, Η. H.: 1954, ‘Geological hypotheses and the earth’s crust under the oceans’, Royal Society of London Proceedings 222 A, 341–348.

Hess, Η. H.: 1955л, ‘Serpentines, Orogeny, and Epeirogeny’, Geological Society of America, Special Paper 62, pp. 391–406.

Hess, Η. H.: 19556, “The Oceanic Crust”, Journal of Marine Reserach 14, 423 - 439.

Hess, Η. H.: 1959л, ‘Nature of the Great Oceanic Ridges’, International Ocean Congress preprints, American Assn. for the Advancement of Science, Washington, D. C., pp. 33–34.

Hess, Η. H.: 19596, The AMSOC Hole to the Earth’s Mantle’, Transactions of the American Geophysical Union 40, 340–345.

Hess, Η. H.: 1960, ‘Evolution of Ocean Basins’, preprint, 37pp.

Download references

You can also search for this author in PubMed   Google Scholar

Editor information

Editors and affiliations.

Department of Philosophy, University of Nevada, Reno, USA

Thomas Nickles

Rights and permissions

Reprints and permissions

Copyright information

© 1980 D. Reidel Publishing Company

About this chapter

Frankel, H. (1980). Hess’s Development of His Seafloor Spreading Hypothesis. In: Nickles, T. (eds) Scientific Discovery: Case Studies. Boston Studies in the Philosophy of Science, vol 60. Springer, Dordrecht. https://doi.org/10.1007/978-94-009-9015-9_18

Download citation

DOI : https://doi.org/10.1007/978-94-009-9015-9_18

Publisher Name : Springer, Dordrecht

Print ISBN : 978-90-277-1093-2

Online ISBN : 978-94-009-9015-9

eBook Packages : Springer Book Archive

Share this chapter

Anyone you share the following link with will be able to read this content:

Sorry, a shareable link is not currently available for this article.

Provided by the Springer Nature SharedIt content-sharing initiative

• Publish with us

Policies and ethics

• Find a journal
• Track your research

• school Campus Bookshelves
• menu_book Bookshelves
• perm_media Learning Objects
• login Login
• how_to_reg Request Instructor Account
• hub Instructor Commons

Margin Size

• Download Page (PDF)
• Download Full Book (PDF)
• Periodic Table
• Physics Constants
• Scientific Calculator
• Reference & Cite
• Tools expand_more
• Readability

selected template will load here

This action is not available.

2.1: Alfred Wegener’s Continental Drift Hypothesis

• Last updated
• Save as PDF
• Page ID 11199

• Chris Johnson, Matthew D. Affolter, Paul Inkenbrandt, & Cam Mosher
• Salt Lake Community College via OpenGeology

\( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \)

\( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)

\( \newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\)

( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\)

\( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\)

\( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\)

\( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\)

\( \newcommand{\Span}{\mathrm{span}}\)

\( \newcommand{\id}{\mathrm{id}}\)

\( \newcommand{\kernel}{\mathrm{null}\,}\)

\( \newcommand{\range}{\mathrm{range}\,}\)

\( \newcommand{\RealPart}{\mathrm{Re}}\)

\( \newcommand{\ImaginaryPart}{\mathrm{Im}}\)

\( \newcommand{\Argument}{\mathrm{Arg}}\)

\( \newcommand{\norm}[1]{\| #1 \|}\)

\( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\AA}{\unicode[.8,0]{x212B}}\)

\( \newcommand{\vectorA}[1]{\vec{#1}}      % arrow\)

\( \newcommand{\vectorAt}[1]{\vec{\text{#1}}}      % arrow\)

\( \newcommand{\vectorB}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \)

\( \newcommand{\vectorC}[1]{\textbf{#1}} \)

\( \newcommand{\vectorD}[1]{\overrightarrow{#1}} \)

\( \newcommand{\vectorDt}[1]{\overrightarrow{\text{#1}}} \)

\( \newcommand{\vectE}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash{\mathbf {#1}}}} \)

Alfred Wegener (1880-1930) was a German scientist who specialized in meteorology and climatology. His knack for questioning accepted ideas started in 1910 when he disagreed with the explanation that the Bering Land Bridge was formed by isostasy and that similar land bridges once connected the continents [ 1 ]. After reviewing the scientific literature, he published a hypothesis stating the continents were originally connected and then drifted apart. While he did not have the precise mechanism worked out, his hypothesis was backed up by a long list of evidence.

Early Evidence for Continental Drift Hypothesis

Wegener’s first piece of evidence was that the coastlines of some continents fit together like pieces of a jigsaw puzzle. People noticed the similarities in the coastlines of South America and Africa on the first world maps, and some suggested the continents had been ripped apart [ 3 ]. Antonio Snider-Pellegrini did preliminary work on continental separation and matching fossils in 1858.

What Wegener did differently was synthesizing a large amount of data in one place. He used the true edges of the continents, based on the shapes of the continental shelves [ 4 ]. This resulted in a better fit than previous efforts that traced the existing coastlines [ 5 ].

Wegener also compiled evidence by comparing similar rocks, mountains, fossils, and glacial formations across oceans. For example, the fossils of the primitive aquatic reptile Mesosaurus were found on the separate coastlines of Africa and South America. Fossils of another reptile, Lystrosaurus, were found in Africa, India, and Antarctica. He pointed out these were land-dwelling creatures could not have swum across an entire ocean.

Opponents of continental drift insisted trans-oceanic land bridges allowed animals and plants to move between continents [ 6 ]. The land bridges eventually eroded away, leaving the continents permanently separated. The problem with this hypothesis is the improbability of a land bridge being tall and long enough to stretch across a broad, deep ocean.

More support for continental drift came from the puzzling evidence that glaciers once existed in normally very warm areas in southern Africa, India, Australia, and Arabia. These climate anomalies could not be explained by land bridges. Wegener found similar evidence when he discovered tropical plant fossils in the frozen region of the Arctic Circle. As Wegener collected more data, he realized the explanation that best fit all the climate, rock, and fossil observations involved moving continents.

Proposed Mechanism for Continental Drift

Figure \(\PageIndex{5}\): [Click to Animate] Animation of the basic idea of convection: an uneven heat source in a fluid causes rising material next to the heat and sinking material far from the heat.

Wegener’s work was considered a fringe science theory for his entire life. One of the biggest flaws in his hypothesis was the inability to provide a mechanism for how the continents moved. Obviously, the continents did not appear to move, and changing the conservative minds of the scientific community would require exceptional evidence that supported a credible mechanism. Other pro-continental drift followers used expansion, contraction, or even the moon’s origin to explain how the continents moved. Wegener used centrifugal forces and precession, but this model was proven wrong [ 7 ]. He also speculated about seafloor spreading, with hints of convection, but could not substantiate these proposals [ 8 ]. As it turns out, current scientific knowledge reveals convection is the major force in driving plate movements.

Development of Plate Tectonic Theory

Wegener died in 1930 on an expedition in Greenland. Poorly respected in his lifetime, Wegener and his ideas about moving continents seemed destined to be lost in history as fringe science. However, in the 1950s, evidence started to trickle in that made continental drift a more viable idea. By the 1960s, scientists had amassed enough evidence to support the missing mechanism—namely, seafloor spreading—for Wegener’s hypothesis of continental drift to be accepted as the theory of plate tectonics. Ongoing GPS and earthquake data analyses continue to support this theory. The next section provides the pieces of evidence that helped transform one man’s wild notion into a scientific theory.

Mapping of the Ocean Floors

In 1947 researchers started using an adaptation of SONAR to map a region in the middle of the Atlantic Ocean with poorly-understood topographic and thermal properties [ 9 ]. Using this information, Bruce Heezen and Marie Tharp created the first detailed map of the ocean floor to reveal the Mid-Atlantic Ridge [ 10 ], a basaltic mountain range that spanned the length of the Atlantic Ocean, with rock chemistry and dimensions unlike the mountains found on the continents. Initially, scientists thought the ridge was part of a mechanism that explained the expanding Earth or ocean-basin growth hypotheses [ 11 ; 12 ]. In 1959, Harry Hess proposed the hypothesis of seafloor spreading – that the mid-ocean ridges represented tectonic plate factories, where a new oceanic plate was issuing from these long volcanic ridges. Scientists later included transform faults perpendicular to the ridges to better account for varying rates of movement between the newly formed plates [ 13 ]. When earthquake epicenters were discovered along the ridges, the idea that earthquakes were linked to plate movement took hold [ 14 ].

Seafloor sediment, measured by dredging and drilling, provided another clue. Scientists once believed sediment accumulated on the ocean floors over a very long time in a static environment. When some studies showed less sediment than expected, these results were initially used to argue against the continental movement [ 15 ; 16 ]. With more time, researchers discovered these thinner sediment layers were located close to mid-ocean ridges, indicating the ridges were younger than the surrounding ocean floor. This finding supported the idea that the seafloor was not fixed in one place [ 17 ].

Paleomagnetism

The seafloor was also mapped magnetically. Scientists had long known of strange magnetic anomalies that formed a striped pattern of symmetrical rows on both sides of mid-oceanic ridges. What made these features unusual was the north and south magnetic poles within each stripe was reversed in alternating rows [ 18 ]. By 1963, Harry Hess and other scientists used these magnetic reversal patterns to support their model for seafloor spreading [ 19 ] (see also Lawrence W. Morley [ 20 ]).

Paleomagnetism is the study of magnetic fields frozen within rocks, basically a fossilized compass. In fact, the first hard evidence to support plate motion came from paleomagnetism.

Igneous rocks containing magnetic minerals like magnetite typically provide the most useful data. In their liquid state as magma or lava, the magnetic poles of the minerals align themselves with the Earth’s magnetic field. When the rock cools and solidifies, this alignment is frozen into place, creating a permanent paleomagnetic record that includes magnetic inclination related to global latitude, and declination related to magnetic north.

Scientists had noticed for some time the alignment of magnetic north in many rocks was nowhere close to the earth’s current magnetic north. Some explained this as part of the normal movement of earth magnetic north pole. Eventually, scientists realized adding the idea of continental movement explained the data better than the pole movement alone [ 21 ].

Wadati-Benioff Zones

Around the same time mid-ocean ridges were being investigated, other scientists linked the creation of ocean trenches and island arcs to seismic activity and tectonic plate movement [ 22 ]. Several independent research groups recognized earthquake epicenters traced the shapes of oceanic plates sinking into the mantle. These deep earthquake zones congregated in planes that started near the surface around ocean trenches and angled beneath the continents and island arcs [ 23 ]. Today these earthquake zones called Wadati-Benioff zones.

Based on the mounting evidence, the theory plate tectonics continued to take shape. J. Tuzo Wilson was the first scientist to put the entire picture together by proposing that the opening and closing of the ocean basins [ 24 ]. Before long, scientists proposed other models showing plates moving with respect to each other, with clear boundaries between them [ 25 ]. Others started piecing together complicated histories of tectonic plate movement [ 26 ]. The plate tectonic revolution had taken hold.

• 1. Fluegel, von H. W. Wegener-Ampferer-Schwinner. Ein Beitrag zur Geschichte der Geologie in Österreich. Mitt. Oesterr. Geol. Ges. 73 , 237–254 (1980).
• 3. Bacon, F. & Montagu, B. The Works of Francis Bacon, Lord Chancellor of England: With a Life of the Author . (Parry & McMillan, 1848).
• 4. Drake, E. T. Alfred Wegener’s reconstruction of Pangea. Geology 4 , 41–44 (1976).
• 5. Mantovani, R. Les fractures de l’écorce terrestre et la théorie de Laplace. Bull. Soc. Sc. et Arts Réunion 41–53 (1889).
• 6. Wells, H. G., Huxley, J. & Wells, G. P. The Science of Life. Philosophy 6 , 506–507 (1931).
• 7. Scheidegger, A. E. Examination of the physics of theories of orogenesis. Geol. Soc. Am. Bull. 64 , 127–150 (1953).
• 8. Jacoby, W. R. Modern concepts of Earth dynamics anticipated by Alfred Wegener in 1912. Geology 9 , 25–27 (1981).
• 9. Tolstoy, I. & Ewing, M. North Atlantic hydrography and the Mid-Atlantic Ridge. Geol. Soc. Am. Bull. 60 , 1527–1540 (1949).
• 10. Heezen, B. C., Tharp, M. & Ewing, M. The Floors of the Oceans I. The North Atlantic. Geological Society of America Special Papers 65 , 1–126 (1959).
• 11. Heezen, B. C. The Rift in the Ocean Floor. Sci. Am. 203 , 98–110 (1960).
• 12. Dietz, R. S. Continent and ocean basin evolution by spreading of the seafloor. Nature 190 , 854–857 (1961).
• 13. Wilson, J. T. A new class of faults and their bearing on continental drift. Nature (1965).
• 14. Heezen, B. C. & Tharp, M. Tectonic Fabric of the Atlantic and Indian Oceans and Continental Drift. Philosophical Transactions of the Royal Society of London A: Mathematical, Physical and Engineering Sciences 258 , 90–106 (1965).
• 15. Ewing, M., Ewing, J. I. & Talwani, M. Sediment distribution in the oceans: The Mid-Atlantic Ridge. Geol. Soc. Am. Bull. 75 , 17–36 (1964).
• 16. Saito, T., Ewing, M. & Burckle, L. H. Tertiary sediment from the mid-atlantic ridge. Science 151 , 1075–1079 (1966).
• 17. Ewing, M., Houtz, R. & Ewing, J. South Pacific sediment distribution. J. Geophys. Res. 74 , 2477–2493 (1969).
• 18. Mason, R. G. A magnetic survey off the west coast of the United-States between latitudes 32-degrees-N and 36-degrees-N longitudes 121-degrees-W and 128-degrees-W. Geophysical Journal of the Royal Astronomical Society 1 , 320 (1958).
• 19. Vine, F. J. & Matthews, D. H. Magnetic anomalies over oceanic ridges. Nature 199 , 947–949 (1963).
• 20. Frankel, H. The Development, Reception, and Acceptance of the Vine-Matthews-Morley Hypothesis. Hist. Stud. Phys. Biol. Sci. 13 , 1–39 (1982).
• 21. Irving, E. Palaeomagnetic and palaeoclimatological aspects of polar wandering. Geofis. pura appl. 33 , 23–41 (1956).
• 22. Coats, R. R. Magma type and crustal structure in the Aleutian Arc. in The Crust of the Pacific Basin 92–109 (American Geophysical Union, 1962). doi:10.1029/GM006p0092
• 23. Wadati, K. On the activity of deep-focus earthquakes in the Japan Islands and neighbourhoods. Geophys. Mag. 8 , 305–325 (1935).
• 24. Wilson, J. T. Did the Atlantic close and then re-open? (Nature, 1966).
• 25. McKenzie, D. P. & Parker, R. L. The North Pacific: an Example of Tectonics on a Sphere. Nature 216 , 1276–1280 (1967).
• 26. Atwater, T. Implications of Plate Tectonics for the Cenozoic Tectonic Evolution of Western North America. Geol. Soc. Am. Bull. 81 , 3513–3536 (1970).

December 1, 1968

Sea-Floor Spreading

Geophysical phenomena ranging from earthquakes to continental drift are being explained by a new theory that gives promise of eventually relating geomagnetism and the earth's internal and orbital dynamics

By J. R. Heirtzler

Global activity of seafloor biodiversity mapped

A team of scientists from the USA and UK has used artificial intelligence (AI) to map the activities of seafloor invertebrate animals, such as worms, clams and shrimps, across all the oceans of the world.

The research, led by Texas A&M University (USA) with investigators from the University of Southampton (UK) and Yale University (USA), combined large datasets, with machine learning techniques, to reveal the critical factors that support and maintain the health of marine ecosystems.

Marine sediments are extremely diverse and cover the majority of the Earth's surface. By stirring up and churning the seafloor -- a process known as 'bioturbation' -- small creatures living in the sediments can have a big impact in regulating global carbon, nutrient and biogeochemical cycles. Rather like worms turning and enriching the soil in our garden, invertebrates are doing the same on the seabed -- improving conditions for ocean life.

Understanding how these processes operate in different regions of the world gives scientists important insights into what is driving the health of oceans and how they may respond to climate change.

This latest study hugely expands this knowledge by, for the first time, providing a way to predict and map the contributions seafloor creatures make at any point around the world.

Findings of the study are published in the journal Current Biology.

"Knowing how bioturbation links to other aspects of the environment means that we are now better equipped to predict how these systems might change in response to climate change," commented Dr Shuang Zhang, lead researcher and assistant professor at the Department of Oceanography, Texas A&M University.

Dr Martin Solan, Professor of Marine Ecology at the University of Southampton adds: "We have known for some time that ocean sediments are extremely diverse and play a fundamental role in mediating the health of the ocean, but only now do we have insights about where, and by how much, these communities contribute. For example, the way in which these communities affect important aspects of ocean ecosystems are very different between the coastlines and the deep sea."

The researchers used existing datasets on sea creature activity and the depth of their sediment mixing -- data sourced from hundreds of test points around the world. By using this information to train from, and relating it to a variety of environmental conditions, the AI was able to make accurate predictions about what is happening in sediment on the seafloor, at any point globally.

The team found that a complex combination of a variety of environment conditions influence bioturbation and that this varies around the world. A multitude of factors, such as water depth, temperature, salinity, distance from land, animal abundance and nutrient availability all play a role. In turn, this affects the activity of invertebrate animals and ultimately the health of ocean ecosystems.

"Through our analysis, we discovered that not just one, but multiple environmental factors jointly influence seafloor bioturbation and the ecosystem services these animals provide," Dr Lidya Tarhan, Assistant Professor at the Department of Earth and Planetary Sciences, Yale University, said. "This includes factors that directly impact food supply, underlying the complex relationships that sustain marine life, both today and in Earth's past."

The team hope their study will help with developing strategies to mitigate habitat deterioration and protect marine biodiversity.

"Our analysis suggests that the present global network of marine protected areas does not sufficiently protect these important seafloor processes, indicating that protection measures need to be better catered to promote ecosystem health." added Dr Lidya Tarhan.

• Marine Biology
• Ecology Research
• Oceanography
• Environmental Awareness
• Dog intelligence
• The evolution of human intelligence
• Game theory
• Paleoclimatology

Story Source:

Materials provided by University of Southampton . Note: Content may be edited for style and length.

Journal Reference :

• Shuang Zhang, Martin Solan, Lidya Tarhan. Global distribution and environmental correlates of marine bioturbation . Current Biology , 2024; DOI: 10.1016/j.cub.2024.04.065

Cite This Page :

Explore More

• Resting Brain: Neurons Rehearse for Future
• Observing Single Molecules
• A Greener, More Effective Way to Kill Termites
• One Bright Spot Among Melting Glaciers
• Martian Meteorites Inform Red Planet's Structure
• Volcanic Events On Jupiter's Moon Io: High Res
• What Negative Adjectives Mean to Your Brain
• 'Living Bioelectronics' Can Sense and Heal Skin
• Extinct Saber-Toothed Cat On Texas Coast
• Some Black Holes Survive in Globular Clusters

Trending Topics

Strange & offbeat.