It is believed that the successive movement of the rocks from the ridge progressively increases the ocean depth and have greater depths in the ocean trenches. Seafloor spreading leads to the renewal of the ocean floor in every million years, a period of time for building a mid-ocean ridge, moving away across the ocean and subduction into a trench.
The highly dense oceanic crust that is formed after a progressive spreading is destined to two possible occurrences. It can either be subducted into the ocean deep trench or continue to spread across the ocean until it reaches a coast. Subduction is the slanting and downward movement of the edge of a crustal plate into the mantle beneath another plate. It occurs when an incredibly dense ocean crust meets a deep ocean trench.
On the other hand, if the ocean crusts continuous to move along the ocean and not found a trench, no subduction will occur. It will continue to spread until a coast is found and literally pushing it away towards its direction. Two possible things could happen in the subduction of ocean crust. Once the subduction occurs, a melting happens due to a tremendous friction. The ocean crust is then melted into magma. The magma could either go back into the mantle for another convection currents leading again to another sea floor spreading or it could burst through a crack in a continental crust and creates a volcano.
Subduction and sea-floor spreading are processes that could alter the size and form of the ocean. For instance, the Atlantic Ocean is believed to be expanding because of its few trenches. Due to this, continuous Seafloor spreading occurs and makes Atlantic Ocean floor to be connected to other continental crust making the ocean gets wider over the time.
On the other hand, the Pacific Ocean has more trenches that lead to more subduction of ocean crusts rather than the formation of the mid-ocean ridge. The Pacific Ocean is believed to be continuing to shrink.
This evidence was from the investigations of the molten material, seafloor drilling, radiometric age dating and fossil ages, and the magnetic stripes. This evidence however was also used to support the Theory of Continental drift.
The condition on the mid-oceanic ridge was substantially different from other surfaces away from the region because of the warmer temperature. He described that the molten magma from the mantle arose due to the convection currents in the interior of the earth.
The flow of the materials goes through the upper mantle and leaks through the plates of the crust. This makes the temperature near the mid-oceanic ridge becomes warm and the other surface to become cold because as the molten magma continues to push upward, it moves the rocks away from the ridge.
The seafloor drilling system led to the evidence that supports the seafloor-spreading hypothesis. The samples obtained from the seafloor drill reveals that the rocks away from the mid-oceanic ridge were relatively older than the rocks near to it.
The old rocks were also denser and thicker compared to the thinner and less dense rocks in the mid-oceanic ridge. This means that the magma that leaks from the ridge pushes the old rocks away and as they increasingly become distant, they more likely become older, denser, and thicker. On the other hand, the newest, thinnest crust is located near the center of the mid-ocean ridge, the actual site of seafloor spreading.
By the use of radiometric age dating and studying fossil ages, it was also found out the rocks of the sea floor age is younger than the continental rocks. It is believed that continental rocks formed 3 billion years ago, however the sediments samples from the ocean floor are found to be not exceeding million years old. Also called lithospheric plate.
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. Jeannie Evers, Emdash Editing. Caryl-Sue, National Geographic Society. 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. Any interactives on this page can only be played while you are visiting our website. You cannot download interactives. These tectonic plates rest upon the convecting mantle, which causes them to move. The movements of these plates can account for noticeable geologic events such as earthquakes, volcanic eruptions, and more subtle yet sublime events, like the building of mountains.
Teach your students about plate tectonics using these classroom resources. Ocean currents are the continuous, predictable, directional movement of seawater driven by gravity, wind Coriolis Effect , and water density.
Ocean water moves in two directions: horizontally and vertically. Horizontal movements are referred to as currents, while vertical changes are called upwellings or downwellings. Explore how ocean currents are interconnected with other systems with these resources. In , after decades of tediously collecting and mapping ocean sonar data, scientists began to see a fairly accurate picture of the seafloor emerge.
The Tharp-Heezen map illustrated the geological features that characterize the seafloor and became a crucial factor in the acceptance of the theories of plate tectonics and continental drift. Today, these theories serve as the foundation upon which we understand the geologic processes that shape the Earth.
The theory of plate tectonics revolutionized the earth sciences by explaining how the movement of geologic plates causes mountain building, volcanoes, and earthquakes. Join our community of educators and receive the latest information on National Geographic's resources for you and your students. Skip to content. Twitter Facebook Pinterest Google Classroom. Encyclopedic Entry Vocabulary. 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. Convection current s carry heat from the lower mantle and core to the lithosphere.
Seafloor spreading occurs at divergent plate boundaries. 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 fracture s and spills onto the crust. This bubbled-up magma is cooled by frigid seawater to form igneous rock.
Seafloor spreading occurs along mid-ocean ridge s—large mountain range s rising from the ocean floor. 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 cliff s and mountains. Rapidly spreading ridges have a much more gentle slopes.
The Mid-Atlantic Ridge, for instance, is a slow spreading center. It spreads centimeters. The East Pacific Rise, on the other hand, is a fast spreading center. It spreads about centimeters 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 ridge—the actual site of seafloor spreading. The age, density, and thickness of oceanic crust increases with distance from the mid-ocean ridge.
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 magnetometer s to measure the magnetism of the ocean floor in the s.
Scientists determined that the same process formed the perfectly symmetrical stripes on both side of a mid-ocean ridge.
0コメント