Harry Hess suggested the theory that the seafloor moves (and carries the continents with it) as it expands from a central axis. According to this idea, the great heat generated by radioactive chemicals in the mantle (100-2900 km below the earth's surface) seeks a way out and causes convection currents to emerge in the mantle.
How does seafloor spreading disprove the theory of continental drift?
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.
What is seafloor spreading and how does it occur?
That is until an American geologist named Henry Hess proposed the radical idea of seafloor spreading, which is essentially the creation and destruction of the ocean floor. Seafloor spreading occurs when the seafloor spreads apart along both sides of a mid-ocean ridge as new crust is added.
Who came up with the theory of continental drift?
The theory of continental drift is most associated with the scientist Alfred Wegener. In the early 20th century, Wegener published a paper explaining his theory that the continental landmasses were “drifting” across the Earth, sometimes plowing through oceans and into each other.
What caused the continents to move apart?
This spreading creates a successively younger ocean floor, and the flow of material is thought to bring about the migration, or drifting apart, of the continents.
How did the continents move according to seafloor spreading theory?
As the magma cools, it is pushed away from the flanks of the ridges. This spreading creates a successively younger ocean floor, and the flow of material is thought to bring about the migration, or drifting apart, of the continents.
What is the hypothesis of seafloor spreading?
Sea-floor spreading — In the early 1960s, Princeton geologist Harry Hess proposed the hypothesis of sea-floor spreading, in which basaltic magma from the mantle rises to create new ocean floor at mid-ocean ridges.
What two additional categories of evidence supported the original seafloor spreading hypothesis?
Harry Hess's hypothesis about seafloor spreading had collected several pieces of evidence to support the theory. This evidence was from the investigations of the molten material, seafloor drilling, radiometric age dating and fossil ages, and the magnetic stripes.
What hypothesis is used to explain the movement of the continents?
Continental drift is the hypothesis that the Earth's continents have moved over geologic time relative to each other, thus appearing to have "drifted" across the ocean bed.
How did seafloor spreading and mantle convection explains Wegener's hypothesis?
Similar to Wegener's theory that continents do in fact move, Hess' seafloor spreading contradicted Wegener's continental drift in that it involved the ocean sea floor moving as it expanded—instead of continents ploughing through the sea.
What is ocean floor spreading and what role does it play in continental drift theory?
This “recycling” process, later named “seafloor spreading,” carries off older sediment and fossils, and moves the continents as new ocean crust spreads away from the ridges. Supporting Wegener's theory of continental drift, Hess explained how the once-joined continents had separated into the seven that exist today.
What are the 3 types of evidence for seafloor spreading?
The pieces of evidence gathered for sea-floor spreading include the evidence from molten material, magnetic stripes, and drilling samples.
How does magnetic striping on the seafloor provide evidence of seafloor spreading?
They stated that the magnetic striping was due to paleomagnetism. The striping revealed magnetic reversals in the Earth's poles as oceanic crust moved away from the mid-oceanic ridges by seafloor spreading.
What theory explains how the plates of the earth are continually moving?
Plate tectonics is a scientific theory that explains how major landforms are created as a result of Earth's subterranean movements. The theory, which solidified in the 1960s, transformed the earth sciences by explaining many phenomena, including mountain building events, volcanoes, and earthquakes.
How did Alfred Wegener explain the movement of continents?
In the early 20th century, Wegener published a paper explaining his theory that the continental landmasses were “drifting” across the Earth, sometimes plowing through oceans and into each other. He called this movement continental drift.
How did the continents move over time?
In 1912, German scientist Alfred Wegener proposed a theory he called continental drift. According to Wegener's theory, Earth's continents once formed a single, giant landmass, which he called Pangaea. Over millions of years, Pangaea slowly broke apart, eventually forming the continents as they are today.
What might have caused the continents to move?
The movement of these tectonic plates is likely caused by convection currents in the molten rock in Earth's mantle below the crust. Earthquakes and volcanoes are the short-term results of this tectonic movement. The long-term result of plate tectonics is the movement of entire continents over millions of years (Fig.
What are 3 types of evidence for seafloor spreading?
The pieces of evidence gathered for sea-floor spreading include the evidence from molten material, magnetic stripes, and drilling samples.
What happens at seafloor spreading?
Sea-floor spreading is what happens at the mid-oceanic ridge where a divergent boundary is causing two plates to move away from one another resulting in spreading of the sea floor. As the plates move apart, new material wells up and cools onto the edge of the plates.
What is one piece of evidence of seafloor spreading?
One piece of evidence leading to the identification of seafloor spreading was that the oldest rocks on the ocean floor were found near the continents and the youngest were found near the ocean ridges.
How does seafloor spreading affect the environment?
Seafloor spreading has all kinds of effects. It can cause sea level rise, pushes tectonic plates around and can affect the amount of carbon dioxide in the atmosphere by powering volcanoes. Fifteen million years ago, the researchers found, the seafloor spread about 200 millimeters per year.
Who proposed the theory of seafloor spreading?
Harry Hess proposed the idea of seafloor spreading in 1960. He used maps created by solar readings of the ocean floor. He explained that seafloor s...
How is seafloor spreading explained and proven?
Seafloor spreading is explained and proven by evidence. Under the oceans lie long mountain chains or ridges. The ocean floor crust on either side o...
What are the main points of the seafloor spreading theory?
The main points of seafloor spreading theory include the idea that molten material moves in at divergent plate boundaries. This movement creates a...
Question: What is Sea-floor Spreading?
Answer: Seafloor spreading is a geologic process in which tectonic plates i.e., the large slabs of Earth's lithosphere split apart from each other.
Question: Who proposed the sea-floor spreading theory?
Answer: Seafloor spreading theory was proposed by the geophysicist Harry H. Hess.
Question: What were the outcomes of sea-floor spreading theory?
Answer: It solved the dilemma of younger crust being discovered at mid-oceanic ridges and older rocks being found as we move out from the ridges mi...
Answer: (b) See the Explanation
The age of the rocks increases as one moves away from the mid oceanic ridges crest. Volcanic eruptions are common along the mid oceanic ridges. Hen...
Answer: (a) See the Explanation
Seafloor spreading is a phenomenon that happens at mid-ocean ridges, where new oceanic crust is formed by volcanic activity and then slowly moves a...
What are ridge crests characterized by?
Research has also revealed that the ridge crests are characterized by anomalously low seismic wave velocities, which can be attributed to thermal expansion and microfracturing associated with the upwelling magma. seafloor spreading in three ocean basins. Patterns of seafloor spreading in the Pacific (left), Arctic (centre), ...
What is the spreading hypothesis of the seafloor?
A veritable legion of evidence supports the seafloor spreading hypothesis. Studies conducted with thermal probes, for example, indicate that the heat flow through bottom sediments is generally comparable to that through the continents except over the mid-ocean ridges, where at some sites the heat flow measures three to four times the normal value. The anomalously high values are considered to reflect the intrusion of molten material near the crests of the ridges. Research has also revealed that the ridge crests are characterized by anomalously low seismic wave velocities, which can be attributed to thermal expansion and microfracturing associated with the upwelling magma.
What is the process of plate tectonics?
plate tectonics: Seafloor spreading. As upwelling of magma continues, the plates continue to diverge, a process known as seafloor spreading. Samples collected from the ocean... The seafloor spreading hypothesis was proposed by the American geophysicist Harry H. Hess in 1960.
What are the anomalous features of the Earth's crust?
The anomalous features are nearly symmetrically arranged on both sides of the axis and parallel the axis, creating bands of parallel anomalies. age of Earth's oceanic crust. The age of Earth's oceanic crust can be presented to show the pattern of seafloor spreading at the global scale. Encyclopædia Britannica, Inc.
How far does molten material wind through the ocean?
On the basis of Tharp’s efforts and other new discoveries about the deep-ocean floor, Hess postulated that molten material from Earth’s mantle continuously wells up along the crests of the mid-ocean ridges that wind for nearly 80,000 km (50,000 miles) through all the world’s oceans.
How old is the seafloor?
The oldest sediments so far recovered by a variety of methods—including coring, dredging, and deep-sea drilling—date only to the Jurassic Period, not exceeding about 200 million years in age. Such findings are incompatible with the doctrine of the permanency of the ocean basins that had prevailed among Earth scientists for so many years.
What is an encyclopedia editor?
Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree. ...
How does oceanic crust affect sea level?
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.
What happens to the seafloor when convection currents move away from each other?
As tectonic plates slowly move away from each other, heat from the mantle’s convection currents makes the crust more plastic and less dense.
What is the process of seafloor spreading?
Seafloor Spreading. Seafloor spreading is a geologic process in which tectonic plate s—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, churn ing motion of Earth’s mantle.
What are the features of the oceanic crust?
Geographic Features. Oceanic crust slowly moves away from mid-ocean ridges and sites of seafloor spreading. As it move s, 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.
Which plate is the Mid Atlantic Ridge?
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.
How is basalt rock determined?
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.
What happens when magma bubbles up?
Hot magma fueled by mantle convection bubbles up to fill these fracture s 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.
IAS Exam Latest Updates
The Seafloor spreading theory was proposed by the geophysicist Harry H. Hess in 1960. It is a phenomenon that happens at mid-ocean ridges, where new oceanic crust is formed by volcanic activity and then slowly moves away from the ridge. The basis of the theory is the fact that the age of the rocks of the seafloor is not the same throughout history.
Ocean Floor Mapping
Mountain ranges, plains, canyons, undersea ridges, deep pits, and other relief characteristics have been discovered on the ocean floor.
Convection Current Theory
The heart of the Seafloor Spreading Theory is Convection Current Theory.
The Distribution of Earthquakes and Volcanoes
When we map the distribution of earthquakes and volcanoes, we find that volcanic activity, earthquakes, and other related events along plate borders are all caused by mantle convection currents.
Palaeomagnetism
Palaeomagnetism, in simple words, refers to the study of the earth's magnetic properties. The magnetic studies have revealed that the ocean floor consists of parallel bands of oceanic crust which have alternating magnetic polarity.
Sea Floor Spreading theory
The process of seafloor spreading happens at mid-ocean ridges, where new oceanic crust is generated by volcanic activity and then progressively travels away from the ridge.
Evidence that supports the Seafloor Spreading Theory
Evidence from Molten Material –Pillow-shaped rocks (rock pillows) indicate that molten material erupted repeatedly from cracks along the mid-ocean ridge and cooled rapidly.
What type of boundary did Tuzo Wilson predict?
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.
What did the magnetic signatures of the seafloor show?
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.
What did Wegener believe?
All this evidence led Wegener to believe that the continents were once connected but had separated and drifted apart.
What did Wegener say about the continents?
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.
What happens when volcanoes erupt?
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.
What did scientists see about the crest of the ridges?
The scientists also observed that the crest of the ridges had a topography that closely resembled volcanic rift zones on land.
Why is the term "continental drift" no longer accurate?
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.
What did Wegener's theory of continental drift not accept?
Scientists did not accept Wegener’s theory of continental drift. One of the elements lacking in the theory was the mechanism for how it works—why did the continents drift and what patterns did they follow? Wegener suggested that perhaps the rotation of the Earth caused the continents to shift towards and apart from each other. (It doesn't.)
What was Wegener convinced of?
Pangaea. Wegener was convinced that all of Earth’s continents were once part of an enormous, single landmass called Pangaea . Wegener, trained as an astronomer, used biology, botany, and geology describe Pangaea and continental drift.
What are the most dynamic sites of tectonic activity?
Some of the most dynamic sites of tectonic activity are seafloor spreading zones and giant rift valleys. In the process of seafloor spreading, molten rock rises from within the Earth and adds new seafloor ( oceanic crust) to the edges of the old. Seafloor spreading is most dynamic along giant underwater mountain ranges known as mid-ocean ridge s.
What are the continents resting on?
Today, we know that the continents rest on massive slab s of rock called tectonic plate s. The plates are always moving and interacting in a process called plate tectonics. The continents are still moving today. Some of the most dynamic sites of tectonic activity are seafloor spreading zones and giant rift valleys.
How are the North American and Eurasian plates separated?
The North American and Eurasian tectonic plates, for example, are separated by the Mid-Atlantic Ridge. The two continents are moving away from each other at the rate of about 2.5 centimeters (1 inch) per year. Rift valley s are sites where a continental landmass is ripping itself apart.
How long ago did Pangaea exist?
Pangaea existed about 240 million years ago. By about 200 million years ago, this supercontinent began breaking up. Over millions of years, Pangaea separated into pieces that moved away from one another. These pieces slowly assumed their positions as the continent we recognize today.
How long have supercontinents been around?
These include Pannotia, which formed about 600 million years ago , and Rodinia, which existed more than a billion years ago.
What mechanism is used to drift continents?
Seafloor spreading is the mechanism for Wegener’s drifting continents. Convection currents within the mantle take the continents on a conveyor-belt ride of oceanic crust that, over millions of years, takes them around the planet’s surface. The spreading plate takes along any continent that rides on it.
What were the pieces that Hess needed?
The features of the seafloor and the patterns of magnetic polarity symmetrically about the mid-ocean ridges were the pieces that Hess needed. He resurrected Wegener’s continental drift hypothesis and also the mantle convection idea of Holmes.
What are the evidences for the seafloor spreading hypothesis?
Reveals how seafloor topography, magnetic polarity, and age are evidence for the sea floor spreading hypothesis.
Why did Harry Hess call his idea an essay in geopoetry?
Harry Hess called his idea “an essay in geopoetry,” possibly because so many ideas fit together so well, or more likely because at the time he didn’t have all the seafloor data he needed for evidence.
What happens when oceanic crust spreads away from the ridge crest?
As oceanic crust forms and spreads, moving away from the ridge crest, it pushes the continent away from the ridge axis.
Where is the oceanic crust created?
Since new oceanic crust is created at the mid-ocean ridges, either Earth is getting bigger (which it is not) or oceanic crust must be destroyed somewhere. Since the oldest oceanic crust was found at the edges of the trenches, Hess hypothesized that the seafloor subducts into Earth’s interior at the trenches to be recycled in the mantle.
Why is the oldest crust coldest?
The oldest crust is coldest and lies deepest in the ocean because it is less buoyant than the hot new crust.