Reader Ant sent me a link to this photo and short article from ZME Science showing a beetle that is way, way old, with jeweled exoskeleton nicely preserved. The caption (the website is starting a “Fossil Friday” feature):
So, here’s a jewel beetle from the Messel Pit, Germany, 47 million years old. It’s fossilized in such a way that it maintains its iridescence and you can still see the contour of the exoskeleton – stunning!
Image via Reddit user archaeopteryxx.
~*~
Just plain WOW.
Wow – beetles are pretty even when squashed & fossilized. I wonder how the iridescence was preserved.
Here’s the dumbest question of the day: Is the iridescence chemical, or physical? That is, is there some chemical of that color, with molecules of it trapped in the beetle’s carapace? Or is it more a “trick” of the light, like the rainbow you see shining off a thin layer of oil on water?
I have no idea, but I think the answer might help with the question of how the iridescence was preserved.
Not a dumb question at all.
Colorants, for the most part either come in the form of pigments or structural colorants. There are also fluorescent colorants.
With pigments, the chemical composition of the material is such that the atomic bonds are more likely to absorb some wavelengths of light (and radiate the energy as heat) than others; the “others” get reflected (or absorbed and re-emitted at the same wavelength).
Something that appears white (the type of styrofoam you find in disposable coffee cups is a superlative example, with PTFE (Teflon) thread tape being “as good as it gets” outside of insanely expensive materials) reflects all (visible) light equally.
Violet and blue pigments typically reflect just a relatively narrow portion of the blue spectrum. Yellow, red, and orange pigments typically act light a high-pass cutoff filter; they absorb most of the blue through green parts of the spectrum and reflect most of the rest, with a sharp transition between the two; the wavelength at which that transition happens determines the hue of the colorant. The bluer greens typically behave like the blues and violets; the yellower greens are generally a mixture of a blue and a yellow. Purples and violets are always a mixture of a blue and a red. Other colors are mixtures of one of those basic types.
Fluorescent colorants absorb high-energy photons of specific wavelengths and re-emit them as lower-energy photons of different wavelengths. Almost all the paper you might have laying around you is fluorescent; it absorbs ultraviolet light and re-emits it as blue. This is done because most paper, especially cheap paper, naturally has a slightly yellowish hue. The addition of the blue light (“stolen” from the UV that you can’t see) helps trick your eyes into seeing it as both whiter and brighter than it really is. Similarly, fluorescent highlighters “steal” light from other wavelengths and re-emit them at the color of the ink, making said ink appear more luminous (brighter) than any regular ink that might be adjacent to it.
Pretty much all pigments fade with age. The energy from the light that does all the absorbing and re-emitting tends to break down the very molecules that are colorful in the first place. Also, oxygen and water vapor and other substances reacts with many such pigments, turning them into other chemical compounds that have different colors.
In contrast to the world of pigments, there’s structural color. Rather than resulting from the absorption and re-emission of photons, structural color depends on reflection and interference. Think not of ink but of prisms and diffraction gratings. You might not think you know what a diffraction grating is…but grab a CD or a DVD; the insanely thin grooves in the surface of the platter act as a reflective diffraction grating, which is what causes the rainbow effect. What happens is that light acting like a wave reflects and refracts and interferes in all sorts of “interesting” ways, including ones that either create different colors depending on the relative angles of the light and the viewer (iridescence) or selectively filters out all but a single wavelength (structural color). Or, often, a combination of the two. The physics involved makes it possible for the resulting color to consist of a very narrow band of wavelengths, which we perceive as a very saturated color. The most intense / pure / saturated colors to be found in nature are structural colors. In the lab, lasers, LEDs, and monochromators (which use one or more diffraction gratings or prisms combined with narrow slits) can be used to produce light that’s similarly spectrally narrow.
Hope that gives you a glimpse down the rabbit hole….
Cheers,
b&
Thanks, Ben! Great overview.
Hmm, I’ve got some lumps of 350 million year old coal (essentially “carbon black”) that might disagree with you. Unless you’re getting fairly astronomical in your meaning of “with age”. Pesky proton instability, alleged.
This is true for general organic pigments – and some inorganic ones – but most simple inorganic pigments are pretty stable. Want a stable black – use carbon. Want a stable green, use chromium III oxide? Want a different, but not quite so stable green? Use malachite (but colour matching is going to be a PITA. OTOH, the Hermitage has still got it’s malachite room). Want a different and even less stable green, use Malachite Green
Not untrue, but much more true for organic dyes and pigments than for inorganic ones. Unstable inorganic pigments … well, changing the hydration state of metal ions (e.g. malachite versus azurite) can often affect the colour ; there’s the old problem of “White Lead” that becomes less white. But generally the bond energies – typically ionic bonds – are so high that they’re not going to be affected by visible photons at human-compatible temperature. At least, not on time scales where you don’t have to worry about that pesky proton instability (alleged).
There’s a guy whose work I’ve read recently who gets rather enthusiastic about structural colours … found it – Andrew Parker, “Seven Deadly Colours” (a Brit, obviously) ISBN 0-7432-5941-6 …
Fascinating subject. My school practical chemistry project – investigating the colour changes in multiple reactions of di-nitro aryl compounds passed the safety review, but never actually produced any worthwhile results because I got lots of tarry messes. But on the other hand, I accidentally produced quite a few “interesting” side reactions with tri-nitro aryl byproducts, azides, and other interesting things.
I think that my chemistry teacher saw right through my cunning plans. But since he did his PhD on nitrogen halides, he recognised the symptoms.
I’m doing that “air of innocence” thing again. Where’s my undepleted uranium?
Thanks for that — you’re right, “pretty much all” was likely too emphatic a qualifier with insufficient qualification. “Almost all of the colorful pigments typically used by humans lose saturation with age” would likely have been better — but then you wouldn’t have been prompted to offer your own expansion on the topic, so I’m glad for my sloppiness in this instance.
…I’m reminded of a demonstration my high school chemistry teacher did on (I think) the first day of class. He had two clear liquids in flasks. Looked like water as he swirled them around. He poured the one into the other (or the two into a third flask — don’t remember) and bam! instant vibrant opaque yellow. I don’t remember if he ever told us what the liquids were, but something at the back of my mind suggests lead was involved. I also vaguely remember the yellow slowly settling to the bottom of the flask, leaving yet another clear liquid on top…but I’m much less confident of that memory.
Your uranium would make for some quite loverly pigments, as I recall — especially including yellow, but I seem to think that’s not the limit of its hue palette. Pity about that whole toxicity and radioactive decay and weapons proliferation thing…were it not for that, I imagine it’d be some really neat stuff to play with….
b&
Google (or even ebaY) for Uranium Glass. It gives me a certain guilty pleasure to serve New Age Woo-ers with wine glasses of uranium glass, and possibly dessert from a uranium glass serving bowl. I keep a UV note-checker in the room, and see if they notice the fluorescence.
Whether I remember to tell them about the nature of the glassware … well it depends on what clap trap they’re coming out with and how much they annoy me.
Of course, after that Manhattan Project thing in the 1940s, people pretty much stopped making uranium glass, so you’re almost restricted to Victorian (boo) and Art Deco stuff (much more interesting).
Undepleted, of course. But you’d guessed that already.
Oooh…sniny! I had no clue. I just might have to ponder acquiring me some. Tanks!
b&
It glows in the dark. For certain values of “dark” that include “deep purple”.
Play some records backwards too. For that real 1970s feeling!
You just got me thinking about what might be the best way to demonstrate fluorescence, but I don’t know if the requisite materials exist.
What I’d need would be a material that both absorbs and re-emits visible light. And, ideally, a relatively monochromatic light source of the same frequency as the absorption. Place the substance on a spectrally neutral white background (Note! These are not as common as most people think!) and then illuminate both with a broad-spectrum light source (sunlight would be ideal) and with the narrowband source.
Anybody who knows of such a substance, do please feel free to rub my nose in it. The light source I could kludge together if need be….
Cheers,
b&
Well, you can put a fluorescent tube in a microwave and it makes the light work. That more demonstrates radio waves and how microwaves work.
That’s an interesting phenomenon, but not the one I’m imagining demonstrating.
Thinking further, I’d also need a narrowband bandpass filter (something that transmits all light save for a very narrow part of the spectrum) at the absorption frequency to fit over the broadband light source. And, ideally, a few more narrowband light sources and filters at different frequencies.
The way the demonstration would work would be like this:
First, you’d start with the unfiltered broadband light, and you’d see the colorful fluorescent object looking brighter than the paper white — what we’re used to from fluorescence. Then you’d turn off the broadband light and turn on the narrowband light. The white paper would appear to be the same color as the narrowband light source, but the fluorescent object would still look the same color — and it’d be the same brightness as before, while the paper would be comparatively dimmer. Then you’d fit the filter over the broadband light, and the paper would slightly (and perhaps almost imperceptibly) change color from white, but the fluorescent object would be very dark and likely a different color. Next, shine different narrowband lights and the paper will take on the color of the lights but the fluorescent object will remain dark. Last, use different narrowband filters and the fluorescent object will resume its brightness.
…and then, for bonus points, you’d use a spectrograph to observe the spectral characteristics of everything….
I’m realizing I likely don’t have the budget for this sort of thing. First, again, I don’t even know if there’re any substances whose absorption and emission frequencies are both visible — or, if they are, how readily available and / or expensive and / or safe and / or stable they are. Next, though it’s not too terribly hard to make a tunable monochromatic light source, narrowband optical filters are typically pretty expensive.
Maybe after I make my way through some other projects, if I remember about it, I’ll get in touch with the local science museum and see if they’d be willing to make an exhibit out of it….
Cheers,
b&
Probably made lead iodide from colorless solutions of potassium iodide and lead nitrate.
Based on a quick Google search, including this result here:
http://www.glogster.com/sethrat/lead-ii-iodide/g-6mesn2gerf6ild76mgfkia0
I think you’re very likely correct.
Thanks!
b&
The latter; interference. Evidently, the layer structure was conserved with clear enough boundaries and changes in refractive index between them. It would be interesting to microprobe the chemical basis of this, if it can be done without ruining the specimen.
Iridescent [“metallic”] colors are the trademark of the Buprestidae [flat-heat word borers/jewel beetles] — though some buprestid adults are dull grey or black [but probably still doing some interesting optical tricks], and many beetles in other families are equally iridescent.
The iridescent reflection in buprestids is from a layered cuticle [eg, not diffraction grating as in some Lepidoptera]. So this is unlikely to survive replacement during fossilization — I think the original chitinous cuticle is present in this fossil.
For more on the buprestid colors, see:
http://rstb.royalsocietypublishing.org/content/366/1565/709.full
[I believe this is not behind a paywall.]
Ty. I see room here for collaboration between the palaeo team and materials characterisation scientists. The good non-destructive experiments would be angle dependence of colour and, especially, polarisation. Non-destructive (attenuated total reflectance, perhaps) vibrational spectroscopy might also help, and should if practicable distinguish between preservation and replacement of organic material. Both better than my original suggestion of microprobing. There is precedent for 25My chitin (http://rstb.royalsocietypublishing.org/content/354/1379/7) but that was in amber, as well as younger
And then there’s this, also in a RS journal and reporting beetles from the same deposit as the one shown above, including two-dimensional Fourier analysis and reflectance microspectrophotometry of fossil multi-layer reflectors in beetle specimens with well-preserved metallic colours…
…my mistake, various other deposits in addition to Messel. This search brings up lots of interesting stuff.
Interesting. Loss of lamination in the outer layers, but preserved deeper in; changes in refractive index from those of original chitin, but presumably (the authors keep on referring to “preserved structures” without making it clear whether this is preserved material, or merely preserved morphology) only minor chemical alteration. But alteration there is, so the colours we see now differ from the original.
And, of course, as your google search shows, the creationists …
Great questions; great answer; and what a magnificent specimen!
Couldn’t agree more! So beautiful!
It most closely reminds me of this:
“Photonic crystals can be formed in different ways. …
In Lamprocyphus augustus, a weevil from Brazil, the chitin exoskeleton is covered in iridescent green oval scales. These contain diamond-based crystal lattices oriented in all directions to give a brilliant green coloration that hardly varies with angle. The scales are effectively divided into pixels about a μmetre wide. Each such pixel is a single crystal and reflects light in a direction different from its neighbours.”
[ http://en.wikipedia.org/wiki/Structural_coloration#Fixed_structures ]
Presumably then fossilization replaced (or even preserved) the original lattice structures sufficiently that the crushed fossil is still iridescent.
I think in this case the fossil has preserved the chitin and some of its structural detail to give it structural color. Chitin is really very durable stuff, plus the Messel formation is known to delicately preserve lots of detail.
The instant I saw the picture, I thought “Messel” – it’s nice to be right.
To your question: Messel is a volcanic Maar, formed by steam explosions when groundwater met the hot rock underneath. So you have an isolated deep pit with practically no current down there, while the flanks are made of fine ash from the explosion, which means very fine sediment constantly being washed into the lake to preserve the features. Add lots of algae due to the high iron content in the volcanic ash and a subtropical climate, and you get anoxic conditions at the deeper water layer – presto, a world heritage site!
Did you also know that it very nearly was turned into a landfill by the authorities?
Let me guess: next up is reader Beetle sending in a link to a fossilized moth…?
b&
Ha ha! I didn’t even notice until you pointed it out!
Which reminds me of when I joined my previous firm. After I’d introduced myself, the manager gestured around the table and introduced “Beetle, Worm, &c.”
He thought he was being terribly witty …
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I’m sure that was the first time in your entire life you’d ever heard such a clever play on your name. One wonders how the manager had the insight to think of it? You must consider yourself truly fortunate to have the opportunity to encounter such genius.
b&
If that ever happens again, burst into tears and run out of the room! 🙂 that’ll teach ’em!
I prefer the turn-green-and-shred-the-jeans technique myself. Though the AIDAN->AID->AIDS has been a bit beyond a dinner-table joke for a couple of decades now.
*A-hem*
If that’s a female, then it’s just a myth….
b&
Created on the sixth day with every creeping thing that creepeth on the earth.
D’oh! Spot the wings – it’s clearly a bird and created on the fifth day (according to one book of magic stories which I’ve read).
And rendered fossilized by an encounter with a Gorgon.
Wow!
Fossilised beetles? Great. What about fossilised ants?
My kids already regard me as a fossil.
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I admit to being a fossil! ;o) Join the club.
Absolutely amaing fossil. Thanks!
damned sticky “z” key! 🙂