What Colour is a Dead Chameleon?

Although there is a link between Alzheimer's and aluminium; if you look in the brains of people who have Alzheimer's disease, you find these build ups of protein called Alzheimer plaques or beta amyloid plaques, and if you look inside those, you can find aluminium ions there.

It's not clear whether the aluminium goes there because the plaque is there and therefore the brain is already abnormal, or whether the aluminium helps to start the process off in the first place.

What we know is that when you cook things in aluminium foil or aluminium pans, because aluminium is a very reactive metal, the surface of the metal is covered in a very thin layer of an oxide - aluminium oxide - and this actually protects the metal from the atmosphere. That's why aluminium doesn't rust like iron does: it's fairly well protected by that oxide layer. This protective layer also means that the aluminium can't actually get into the food in any appreciable amount. The exception to this is if you cook very, very acidic foods in your aluminium pot, and a good example of this Rhubarb.

Rhubarb is extremely acidic and if you make a rhubarb crumble in an aluminium cooking pan, you will find that it needs virtually no cleaning afterwards because the acid attacks the oxide layer and can liberate a small amount of aluminium from the pan and this can get into the food.

Whether that will then produce Alzheimer's disease subsequently is a bone of contention.

People say that you're advised not to cook very acidic foods in aluminium-rich cooking materials and utensils because there is a small risk that you might get aluminium in the food and it could therefore have health consequences.

Some of the interpretation is based on what happened to people in - I think it was Castleford - in Devon, England, where they accidentally dumped a whole lot of aluminium in a drinking water settling tank.

Aluminium is used in swimming pools and at sewage works as a flocculent. It causes small particles to clump together. They accidentally put some aluminium in a tank that people were going to drink from, rather than the tank they wanted to settle out.

So some people were receiving very high doses of aluminium and there were some alleged connections with Alzheimer-type changes in people subsequently, but we don't know if those people were just going to get Alzheimer's anyway.

So it's a good question. It's open to debate. But don't cook acidic things in those sorts of pans. That would be my advice...

Chris -   A remarkable paper was published in the journal Science recently. An international team led by Roy Wogelius from the University of Manchester has developed a new technique that reveals the colour, and even chemistry, of fossil birds - birds that are more than 100 million years old.

The team used high-powered X-rays to detect trace metals in the fossils and related these to melanin pigments in modern birds. Unlike other methods, the process doesn't involve damaging the fossils. Planet Earth Podcast presenter, Richard Hollingham, went to meet Roy and see the fossils for himself...

Roy -   This is a 50 million year old fossil feather.

Richard -   And it's almost perfect. They're very fine, wispy strands.

Roy -   This is the kind of thing that we call exceptional preservation. You can see the central shaft and we can see the barbs that fan out from either side. The preservation is absolutely splendid.

Richard -   So this is 50 million years old and you can tell from a fossil with your technique the chemistry and from that perhaps the colour of it?

Roy -   That's exactly right. We know that the pigments in our hair and skin bind up with certain metals: Iron, calcium, zinc and copper. Copper is part of the enzyme that actually makes the pigment in our hair and skin and in bird feathers. So we thought that maybe by mapping the trace metals we could see if there's some kind of information about colouration, indeed maybe the colour that you're seeing, this preserved colour maybe that-

Richard -   That's real?

Roy -   Yeah, maybe that's real. And indeed what we found is at the base of this feather there are higher concentrations of copper than anywhere else in this sample, much higher than in the sedimentary rock and much higher than in the top portion of the feather. The other thing we're able to do using x-rays is, not just map the copper but also look and get the details of how the copper is chemically bound, what elements surround it. In other words does it look like an organic compound or is it a purely inorganic compound? And the thing that we found absolutely blew me away; the copper chemistry in the base of this feather is nearly identical to the copper chemistry in melanin sampled from existing organisms.  And so maybe we should go to the other specimen which is perhaps a bit more exciting.

Richard -   It's very well wrapped, in bubble wrap and then tissue paper - let's pull back the tissue paper.  Now that is incredible.  I suppose it's the size of a large crow that's been flattened.

Roy -   Welcome to our 120 million year old road kill. What's amazing about it is that this is the first documented bird with a beak.

Richard -   Oh yes! And again on here you've got colour. You've got much darker wings than the bones in here which are almost a bone colour, even though this is a fossil. But, again, how do you know these colours are real?

Roy -   What you can see here is that in the neck region and around the body there's this very, very dark colouration-

Richard -   Almost black.

Roy -   Yeah, that's right, almost like carbon black. And if you look at the flight feathers which are splayed around to either side of the body, the top has this relatively dark black colouration and then as we move away in the flight feathers and go further and further away from the body they get lighter and lighter in colour.  And what we find is that in the neck region and body region there's very, very high concentrations of copper.  We've also done infrared analyses on these regions and infrared spectra look exactly the same as modern day melanin.  We've done structural work and all this information sits together to tell us that the downy body feathers on this bird were very, very rich in this dark black umelanin pigment.

Richard -   So this was some sort of black bird?

Roy -   That's right, that's exactly right. It's unambiguously non-destructively and over the whole organism we can pull out patterns without having to destroy anything.

Richard -   Now this is fascinating - is this useful?

Roy -   There are aspects of behaviour and evolution and ecology that were inaccessible to palaeontologists until they could start to see colour patterning.  That tells us an awful lot about camouflage, sexual display, a whole different range of behaviours which you really can't get any kind of clue from just bone material, so it's the soft tissue.  So for the palaeontologists it's one of the reasons why they're so interested in this.  This really might be able to tell them something about behaviour.  These trace metals contribute to biochemical pathways, they're still present, we know we can map them and I think this gives us hope that things besides pigmentation actually become available to us as we study ancient life.

Chris - The way that antiperspirant deodorants work, most of them are spray-ons, some roll-ons, they tend to contain lots of zirconium, aluminium zirconium salts and pro-hydrate salts.

The way they work is that you rub them on your skin and they form a layer on the surface of the skin, and wherever they come into contact with water from your own body, in other words, where there's a pore linked to a sweat gland under the skin, they soak up the water and then they form a little plug of gel-like substance inside the sweat gland, stopping any more water coming out.

If you, therefore, stop the water coming out, the skin surface becomes drier. And the reason that we want to make the skin surface drier is that if you have dead skin and water together in a warm wet place, you've got the perfect bacterial banquet. It's these bacteria eating your dead skin, flourishing and thriving in this warm, damp environment that makes the whiff that we want to avoid.

So, we tend to apply the deodorants where we sweat the most and you tend to sweat in those places for various reasons. One of them can be thermal. You do sweat to cool down because when you sweat, you put a thin layer of water on the skin surface. The water is exploiting an effect called the latent heat of vaporisation. In order for the water to go from a liquid into a gas, it has to rob extra energy from the skin surface to break the molecules apart. They're all sticking together as a liquid and to separate out as a gas it needs extra energy to do that and so, when you've got the water on the skin surface, it's taking the extra energy away and that cools you down very efficiently, and that's why we sweat.

Sweating is also under the control of something called the sympathetic nervous system, which means that it's under the control of a part of your nervous system that you activate when you're worried about things. So people can also break into a sweat when they're panic stricken, anticipating having to run away very fast, and things like that. As a result of that, you can also sweat everywhere on your body for a variety of non-thermal reasons. So, just putting on antiperspirant deodorant won't necessarily affect the rate of sweating on other bits of the body because if you're doing a stressful job, you might just sweat elsewhere.

Dave - But, I guess, if you're sweating for thermal reasons then you're going to have less skin to lose the heat from [if you apply anti-perspirant deodourant], so the rest of you is going to be slightly hotter so you might sweat a bit more of the rest?

Chris - I take your point, but I would say, the skin area that you're applying antiperspirant to is such a tiny fraction compared with the whole of the rest of your body that it probably is going to make almost zero difference.

Helen - You would want to basically take the glowing gene from a jellyfish of some sort, and I'm sure there are some out there that grow redor are coloured red. Red is a bit rare in the deep sea but there are some fish in fact that produce red light. [You could] take the gene that produces that light in those species in the deep and stick it in a reindeer's nose. We've done it with mice. We've made glowing green mice. I don't see why we shouldn't be able to make a glowing red reindeer then.

Chris - There is green fluorescent protein which is found in jellyfish, and then there's a tweak that scientists made to make red fluorescent protein, so the green equivalent in red. So it could be expressed. I think there probably are gene sequences that could direct the gene to only turn on in the nose, so you probably could end up with Rudolph. Helen - I'm not saying we should direct our research money to such a frivolous event but it might be quite fun!