Is seafloor spreading a law or theory?
Seafloor spreading is the mechanism by which new seafloor lithosphere is constantly being created at mid-ocean ridges. This theory, introduced by Harry Hess, was proven as patterns of magnetic field polarity preserved in seafloor basalt and by age dating of the rocks.
When was the theory of seafloor spreading accepted?
Building on the work of English geologist Arthur Holmes in the 1930s, Hess’ research ultimately resulted in a ground-breaking hypothesis that later would be called seafloor spreading. In 1959, he informally presented this hypothesis in a manuscript that was widely circulated.
Where does seafloor spreading happen?
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.
At which boundary is seafloor destroyed?
At convergent plate boundaries, oceanic crust is often forced down into the mantle where it begins to melt. Magma rises into and through the other plate, solidifying into granite, the rock that makes up the continents. Thus, at convergent boundaries, continental crust is created and oceanic crust is destroyed.
Is seafloor destroyed?
Basaltic magma forming at mid-ocean ridges serves as a kind of “tape recorder”, recording the Earth’s magnetic field as it reverses through time. The oldest known ocean floor is dated at about 200 million years, indicating that older ocean floor has been destroyed through subduction at deep-sea trenches.
What are two pieces of evidence that support seafloor spreading?
Look at Figure 19 to see the process of sea-floor spreading. Several types of evidence from the oceans supported Hess’s theory of sea-floor spreading-evidence from molten material, magnetic stripes, and drilling samples. This evidence also led sci- entists to look again at Wegener’s theory of continental drift.
Which is the first step in seafloor spreading?
1. A long crack in the oceanic crust forms at a mid ocean ridge. 2. Molten material rises and erupts along the ridge.
What happens to the seafloor at trenches?
Trenches are formed by subduction, a geophysical process in which two or more of Earth’s tectonic plates converge and the older, denser plate is pushed beneath the lighter plate and deep into the mantle, causing the seafloor and outermost crust (the lithosphere) to bend and form a steep, V-shaped depression.
What rock is the seafloor made of?
As old oceanic crust is subducted and melted into magma, new oceanic crust in the form of igneous rock is formed at mid-ocean ridges and volcanic hotspots.