# The Earth's crust 20% sponge?
**URL:** https://boards.straightdope.com/t/the-earths-crust-20-sponge/366093
**Category:** Factual Questions
**Created:** [July 26, 2006, 3:08pm UTC](https://boards.straightdope.com/t/the-earths-crust-20-sponge/366093 "2006-07-26T15:08:56Z")
**Posts on this page:** 20
**Page:** 1
### Author:  [@Pushkin](https://boards.straightdope.com/u/Pushkin)
#### Post date: [July 26, 2006, 3:08pm UTC](https://boards.straightdope.com/t/the-earths-crust-20-sponge/366093/1 "2006-07-26T15:08:56Z")
I was watching an old edition of QI, a quiz show on the BBC here in the UK that prides itself on extreme accuracy.
During the course of one question, it was mentioned that quartz is stronger than a shark’s tooth. We were then told that 20% of the Earth’s crust is quartz which is the remains of animals like sponges. True?
And on the subject of sponges, if a couple of different species of sponge were shredded using a sieve for example and the resulting goop drained into a tank of salt water, eventually the individual sponges would separate from each other and the whole individual sponges would reform. True?
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### Author:  [@VunderBob](https://boards.straightdope.com/u/VunderBob)
#### Post date: [July 26, 2006, 3:16pm UTC](https://boards.straightdope.com/t/the-earths-crust-20-sponge/366093/2 "2006-07-26T15:16:10Z")
> [@Pushkin](#):
>
> I was watching an old edition of QI, a quiz show on the BBC here in the UK that prides itself on extreme accuracy.
>
> During the course of one question, it was mentioned that quartz is stronger than a shark’s tooth. We were then told that 20% of the Earth’s crust is quartz which is the remains of animals like sponges. True?
Wrong, in that quartz is an igneous rock, meaning it is of volcanic origin, and is a silicon based compound.
The 20% is calcium carbonate (limestone), which is sedimentary animal remains. Made up of bones and seashells…
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### Author:  [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)
#### Post date: [July 26, 2006, 3:25pm UTC](https://boards.straightdope.com/t/the-earths-crust-20-sponge/366093/3 "2006-07-26T15:25:28Z")
> [@Pushkin](#):
>
> During the course of one question, it was mentioned that quartz is stronger than a shark’s tooth. We were then told that 20% of the Earth’s crust is quartz which is the remains of animals like sponges. True?
False. Quartz is silicon and oxygen, SiO[sub]2[/sub], an igneous rock that comes from volcanoes. Sponges, being animals, would contain minerals like carbon and calcium. This notion is actually sillier than oil coming from dinosaurs.
From Richard Fortey’s _Earth_:
> [@](#):
>
> Because oxygen forms 46.6% by weight of the elements in the earth’s crust, and silicon 27.7 per cent, it is not surprising that silicate minerals that include those two elements are the most abundant materials in the construction of the earth above the core. All the most common igneous rocks are combinations of different silicate materials.
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### Author:  [@lieu](https://boards.straightdope.com/u/lieu)
#### Post date: [July 26, 2006, 4:27pm UTC](https://boards.straightdope.com/t/the-earths-crust-20-sponge/366093/4 "2006-07-26T16:27:59Z")
Sponges may have internal structures composed of spicular opaline silica or, less commonly, calcium carbonate. These spicules may accumulate in layered deposits but I’d characterize them as more “cherty” than quartz-like and they certainly don’t begin to approximate 20% of the Earth’s crust.
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### Author:  [@Ludovic](https://boards.straightdope.com/u/Ludovic)
#### Post date: [July 26, 2006, 4:41pm UTC](https://boards.straightdope.com/t/the-earths-crust-20-sponge/366093/5 "2006-07-26T16:41:38Z")
It’s not the Earth, but rather, the world of human wreckage that’s 20% Sponge.
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### Author:  [@santallum](https://boards.straightdope.com/u/santallum)
#### Post date: [August 4, 2011, 4:10pm UTC](https://boards.straightdope.com/t/the-earths-crust-20-sponge/366093/6 "2011-08-04T16:10:56Z")
I have seen this episode of QI several times, and listened intently to what was said about
sponges and “quartz” … Steven Fry did not state that 20% of the earths crust originated from sponges, or that all quartz originated from sponges … Fry talked about chert / chalcedony / flint (which are all the same chemical as quartz : SiO2) originating from sponges. He did not even state that all flint originated from sponges. What was said was confusing and rather muddled (so no wonder so many of you misunderstood what was being said) … It seems a reasonable assumption that flint / cert / chalcedony found in limestone areas does indeed originate from the silcon from sponges, just as the limestone there originates from the calcium carbonate (CaCO3) from shells and bones
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### Author:  [@santallum](https://boards.straightdope.com/u/santallum)
#### Post date: [August 4, 2011, 4:14pm UTC](https://boards.straightdope.com/t/the-earths-crust-20-sponge/366093/7 "2011-08-04T16:14:42Z")
Its perhaps suprising that Fry did not mention that SiO2 is glass is quartz is flint is chert is chalcedony is chrysoprase is jasper is amethyst (etc) , as all these things are the different forms of the same chemical compound Silicon Dioxide … marvelous stuff
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### Author:  [@dracoi](https://boards.straightdope.com/u/dracoi)
#### Post date: [August 4, 2011, 4:18pm UTC](https://boards.straightdope.com/t/the-earths-crust-20-sponge/366093/8 "2011-08-04T16:18:29Z")
> [@Pushkin](#):
>
> And on the subject of sponges, if a couple of different species of sponge were shredded using a sieve for example and the resulting goop drained into a tank of salt water, eventually the individual sponges would separate from each other and the whole individual sponges would reform. True?
Absolutely not true. Sponges do have a pretty good ability to regenerate - cut one in half and you wind up with two small sponges that would grow independently from them on. If you shredded them, though, you’d just have a whole mess of dead sponge.
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### Author:  [@aerodave](https://boards.straightdope.com/u/aerodave)
#### Post date: [August 4, 2011, 5:20pm UTC](https://boards.straightdope.com/t/the-earths-crust-20-sponge/366093/9 "2011-08-04T17:20:02Z")
> [@Ludovic](#):
>
> It’s not the Earth, but rather, the world of human wreckage that’s 20% Sponge.
Bravo… 🙂
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### Author:  [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)
#### Post date: [August 4, 2011, 5:37pm UTC](https://boards.straightdope.com/t/the-earths-crust-20-sponge/366093/10 "2011-08-04T17:37:47Z")
> [@Ludovic](#):
>
> It’s not the Earth, but rather, the world of human wreckage that’s 20% Sponge.
I’m lost by your post, lost and found and I can’t touch the ground.
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### Author:  [@Ferret\_Herder](https://boards.straightdope.com/u/Ferret_Herder)
#### Post date: [August 4, 2011, 6:33pm UTC](https://boards.straightdope.com/t/the-earths-crust-20-sponge/366093/11 "2011-08-04T18:33:24Z")
> [@engineer\_comp\_geek](#):
>
> I’m lost by your post, lost and found and I can’t touch the ground.
Well, I’m plowed into the sound.
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### Author:  [@Smeghead](https://boards.straightdope.com/u/Smeghead)
#### Post date: [August 4, 2011, 7:06pm UTC](https://boards.straightdope.com/t/the-earths-crust-20-sponge/366093/12 "2011-08-04T19:06:40Z")
> [@dracoi](#):
>
> Absolutely not true. Sponges do have a pretty good ability to regenerate - cut one in half and you wind up with two small sponges that would grow independently from them on. If you shredded them, though, you’d just have a whole mess of dead sponge.
I have actually seen the experiment done on some nature show. They’re not being “shredded”, exactly, just reduced to individual - but intact - cells. Those cells do reassemble over the next few days and weeks. I haven’t done it firsthand, but I believe the source I saw was quite reliable.
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### Author:  [@njtt](https://boards.straightdope.com/u/njtt)
#### Post date: [August 4, 2011, 7:10pm UTC](https://boards.straightdope.com/t/the-earths-crust-20-sponge/366093/13 "2011-08-04T19:10:10Z")
**The Earth’s crust 20% sponge**
With delicious layers of jam in between.
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### Author:  [@santallum](https://boards.straightdope.com/u/santallum)
#### Post date: [August 4, 2011, 7:56pm UTC](https://boards.straightdope.com/t/the-earths-crust-20-sponge/366093/14 "2011-08-04T19:56:33Z")
SiO2 is also :
citrine
obsidian
black tectite
moldavite
agates (all of them)
and many more I cant remember off the top of my head
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### Author:  [@santallum](https://boards.straightdope.com/u/santallum)
#### Post date: [August 4, 2011, 7:58pm UTC](https://boards.straightdope.com/t/the-earths-crust-20-sponge/366093/15 "2011-08-04T19:58:15Z")
as for the shredding sponges thing
I seem to remember seeing something about that on the Jaques Cousteau TV series
many years ago … ring any bells ??
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### Author:  [@Cartooniverse](https://boards.straightdope.com/u/Cartooniverse)
#### Post date: [August 4, 2011, 8:41pm UTC](https://boards.straightdope.com/t/the-earths-crust-20-sponge/366093/16 "2011-08-04T20:41:45Z")
> [@njtt](#):
>
> **The Earth’s crust 20% sponge**
>
> With delicious layers of jam in between.
You can’t eat your meat if you don’t have any pudding.
How can you have any pudding if you don’t eat your meat ???
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### Author:  [@Don\_t\_Panic](https://boards.straightdope.com/u/Don_t_Panic)
#### Post date: [August 4, 2011, 8:53pm UTC](https://boards.straightdope.com/t/the-earths-crust-20-sponge/366093/17 "2011-08-04T20:53:35Z")
> [@Pushkin](#):
>
> prides itself on extreme accuracy
I dunno about that. If you’re having a QI marathon one of these days, then “spot the horrendous mistake” is usually good for a drinking game. I have a feeling it’s getting worse as the seasons go on, too.
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### Author:  [@Tom\_Tildrum](https://boards.straightdope.com/u/Tom_Tildrum)
#### Post date: [August 4, 2011, 9:04pm UTC](https://boards.straightdope.com/t/the-earths-crust-20-sponge/366093/18 "2011-08-04T21:04:51Z")
So, is it true that 20% of the SDMB’s crust is made up of the sedimentary remains of old threads?
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### Author:  [@mac\_bolan00](https://boards.straightdope.com/u/mac_bolan00)
#### Post date: [August 5, 2011, 12:31am UTC](https://boards.straightdope.com/t/the-earths-crust-20-sponge/366093/19 "2011-08-05T00:31:48Z")
> [@Pushkin](#):
>
> I was watching an old edition of QI, a quiz show on the BBC here in the UK that prides itself on extreme accuracy.
>
> During the course of one question, it was mentioned that quartz is stronger than a shark’s tooth. We were then told that 20% of the Earth’s crust is quartz which is the remains of animals like sponges. True?
quartz is harder than a shark’s tooth. almost 99% of the earth’s crust is composed of various silicates but quartz as a free and distinct mineral is not likely to account for 20% of the crust (i could be wrong though, 20% seems close if you consider the quartz-rich continental granitic masses.)
majority of the crust (and even the mantle) is composed of heavy and dark iron- and magnesium-rich silicates such as basalts and gabbro, peridotites and dunites. these rocks are low in quartz content. it is the continental masses that float over these dark rocks that are (light) granitic and contain a lot of quartz.
having said that, sedimentary remains of animals form only a very thin carapace over the surface of the crust (and not the entire surface, just a small portion.)
> [@](#):
>
> And on the subject of sponges, if a couple of different species of sponge were shredded using a sieve for example and the resulting goop drained into a tank of salt water, eventually the individual sponges would separate from each other and the whole individual sponges would reform. True?
yes, poriferas display the best regenerative abilities in the animal kingdom. your word-for-word account of a sponge pushed through a sieve and coming out whole again is straight out of the guiness book.
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### Author:  [@Tangent](https://boards.straightdope.com/u/Tangent)
#### Post date: [August 5, 2011, 2:57am UTC](https://boards.straightdope.com/t/the-earths-crust-20-sponge/366093/20 "2011-08-05T02:57:31Z")
> [@Ferret\_Herder](#):
>
> Well, I’m plowed into the sound.
I’ll say a prayer for you.
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