Seafloor Spreading for Dummies, the Rewrite - The Freelance Files MMCCXXXVI

Convection and seafloor spreading

While we applaud the fact that someone at Leaf Group has A) realized that a large fraction of the company's content is bogus and B) enlisted "experts" to review new and rewritten content, we truly wish that some of their rewrites corrected the content instead of merely rehashing and expanding on the dumbassery that was already there. Unfortunately, that's not always true. A case in point is the work of rewrite "expert" Marina Somma and her reviewer, Sylvie Tremblay, M. Sc. Take, for example, the Sciencing.com post "What Is the Primary Force That Causes the Seafloor to Spread?"

Somma's assignment was to rewrite a 2013 post by Scott Thompson, which had failed miserably in its attempt to answer the question. According to Thompson, seafloor spreading is caused by rising magma that splits the seafloor in two. We humbly submit that rising magma is an effect of seafloor spreading, not a cause. Unfortunately, Somma seemed equally incompetent to answer the question – in fact, she didn't answer it – something we knew almost immediately when we read this rubbish:

"Tectonic plates are massive slabs of the lithosphere that 'float' along the molten mantle of the Earth."

The presence of the word "molten" is a dead giveaway that Somma (not to mention Tremblay) is well outside her comfort area with this topic. The mantle is not molten in any sense humans can detect; it is an extremely viscous fluid over geologic time. Think frozen peanut butter, and perhaps you'll understand "extremely viscous fluid." So let's look at a few of the other interesting things Marina had to say...

• "The seafloor shifts and changes, particularly in certain regions where separate tectonic plates meet." – Other than where "separate tectonic plates meet" – a clumsily redundant construction – the seafloor is pretty much inert.
• "Oceanic boundaries that move away from one another result in seafloor spreading." – Well, actually those are tectonic plate boundaries, and are not necessarily within oceans. Think East Africa Rift, which will someday millions of years hence be the center of a new ocean.
• "Two sections of the seafloor spread away from one another. This occurs through the movement and shifting of the tectonic plates under the ocean. " – Somma was getting close: now is where she should explain the cause of that "movement and shifting"; ostensibly the reason she wrote this dreck.
• "When two tectonic plates move away from one another, they leave a gap for the molten rock in the mantle to rise to the surface. " – It's even more complicated: the release of pressure by thinning of the crust causes melting of the mantle, which rises due to buoyancy.

Marina went on from this point to discuss rates of spreading (not germane to the question) and the two other types of plate boundaries (also not germane). So, did she ever answer the original question?

Well, no. In fact, Thompson (in his now-deleted version of the "information") tangentially mentioned the force most scientists believe to cause all plate tectonics:

"Convection forms into currents that drive the tectonic plates either together or apart."

That's pretty much it: eight or so convection cells rotating within the mantle cause the overlying plates of lithosphere to move. Where two adjacent cells rotate in divergent directions, the overlying plates move apart. That causes rifting of the crust, with ensuing injection of melted mantle material into the gap. Since that material is denser than continental crust, the newly-created oceanic crust sinks as it cools, creating a basin. Over millions of years, voila: an ocean basin, with a spreading center in the middle.

It's too bad our Dumbass of the Day didn't say something like that instead of wasting more than 200 words to discuss rates of spreading and the relief of the ridges created. But what can you expect of a marine biologist trying to explain whole-earth geophysics?

SI - TECTONICS