Debate and Search For Mechanism
At the Mid-Atlantic Ridge (and other places), material from the upper mantle rises through the faults between oceanic plates to form new crust as the plates move away from each other, a phenomenon first observed as continental drift. When Alfred Wegener first presented a hypothesis of continental drift in 1912, conservative geologists, especially in North America, demanded to know where the motive force could possibly lie. Wegener suggested that the continents ploughed through the ocean crust.
Since then, it has been shown that the motion of the continents is linked to seafloor spreading. In the 1960s, the past record of geomagnetic reversals was noticed by observing the magnetic stripe "anomalies" on the ocean floor. This results in broadly evident "stripes" from which the past magnetic field polarity can be inferred by looking at the data gathered from simply towing a magnetometer on the sea surface or from an aircraft. The stripes on one side of the mid-ocean ridge were the mirror image of those on the other side. The seafloor must have originated on the Earth's great fiery welts, like the Mid-Atlantic Ridge and the East Pacific Rise.
The driver for seafloor spreading in plates with active margins the weight of the cool, dense, subducting slabs that pull them along. The magmatism at the ridge is considered to be "passive upswelling", which is caused by the plates being pulled apart under the weight of their own slabs. This can be thought of as analogous to a rug on a table with little friction: when part of the rug is off of the table, its weight pulls the rest of the rug down with it.
Read more about this topic: Seafloor Spreading
Famous quotes containing the words debate, search and/or mechanism:
“What I think the political correctness debate is really about is the power to be able to define. The definers want the power to name. And the defined are now taking that power away from them.”
—Toni Morrison (b. 1931)
“When you start with a portrait and search for a pure form, a clear volume, through successive eliminations, you arrive inevitably at the egg. Likewise, starting with the egg and following the same process in reverse, one finishes with the portrait.”
—Pablo Picasso (1881–1973)
“When one of us dies of cancer, loses her mind, or commits suicide, we must not blame her for her inability to survive an ongoing political mechanism bent on the destruction of that human being. Sanity remains defined simply by the ability to cope with insane conditions.”
—Ana Castillo (b. 1953)