Lithosphere for Earth Science Dummies

Difference between oceanic and continental lithosphere

Every once in a great while our researchers run across a combination of Q and A that is downright hilarious. Most of the posts that achieve this high honor are at content farms,  especially the ones where people are (allegedly) answering questions. You do know we're talkin' about eHow.com, right? Here's one such post: someone wanted to know, "What Percent of the Earth Is Covered by the Lithosphere?" and eHow's Susan Sherwood was right there to give the OQ an answer. Never mind that the answer, now at Sciencing.com, was just as stupid as the question...

The question's stupid because, except perhaps for a few volcanic vents in rift zones, 100% of the earth's surface is covered by lithosphere. Well, maybe a few thousand km² of mantle are exposed somewhere in the Atlantic, but that's out of about 200,000,000 km²... Anyway, Sherwood didn't provide that answer; instead she launched into a discussion of the two types of lithosphere. Along the way, however, she made a few mistakes:

1. "The crust varies in thickness. Under the oceans it is only 3 to 5 miles deep, but the continental crust extends about 25 miles." 
2. "Below the crust, the top layer of the upper mantle is also part of the lithosphere. With the crust and mantle section combined, the lithosphere is about 50 feet deep. "

And that's all she wrote. Here with corrections is our staff Labrador Retriever (who apparently knows more about geology than Sherwood):

1. The crust is three to six miles thick, not "deep."
2. Oceanic lithosphere is 30 to 50 miles thick; continental lithosphere is about 80 miles thick. Nowhere is it "about 50 feet deep"!
3. Oh, and while we're at it? Oceanic lithosphere covers about 70% of the planet's surface, continental lithosphere covers the rest.

We sure do think that an "educator" who claims to have a PhD would 1) answer the question (Susan didn't) and 2) demonstrate a knowledge of simple scientific terminology: what lousy-ass school doesn't teach  its students the difference between thickness and depth? But the crowning glory of Sherwood's nomination is that crap about "50 feet"! What an idiot! What? A Dumbass of the Day!

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