The Colours of People

Everywhere you look, there are people. Different sizes, different shapes, different colours. And that’s pretty awesome.

But why do I have green eyes, my mum has blue and my dad has hazel?
Why is my hair a shade of browny blonde but my sisters is almost black?
And why oh why do I have to roast myself in the sun to get any form of tan that some people just have naturally??

 

greeneyes


All of the colour differences between people stems from pigments – any substance found within our cells which colours us in some sort of way.

It is the special kind of pigment, melanin which is to blame for any of your 3 major body colourings: eyes, hair & skin. 

Melanin

Melanin is made within melanosomes which are found in cells called melanocytes.

Three important types of melanin include:

  1. Eumelanin = dark pigment 
  2. Phaeomelanin = light pigment 
  3. Neuromelanin = responsible for colouring regions of the brain – problems with neuromelanins are linked to Alzheimers and Parkinsons diseases.

The amount of these types of melanin we each get is determined genetically.

 

Melanindiagram

Eyes

In our eyes, the melanin is found in the iris (the coloured part surrounding the pupil). The top layer of the iris is called the stroma and this is where those melanocytes are found.

Eyediagram

More melanin will result in dark brown or black eyes. With over 55% of the world rocking them, brown eyes are the most popular eye colour.
Less melanin means blue, green or hazel eyes. Green eyes are the rarest in the world with approximately only 2% of the worlds population having them. 

Skin

In our skin, those melanocytes are commonly found in our deepest layer of skin, the basal layer. There are many factors which determine skin colour and it comes down to the size, distribution, shape and number of melanosomes plus how active the melanin within them is. It also takes into account the gene protein melanocortin 1 receptor (MC1R).

redheadMore MC1R activity = more eumelanin, less phaeomelanin. 

Some people have sort-of faulty MC1R genes and they are likely to have red hair, pale skin and freckles. 

Very simply, if you have high amounts of eumelanin but low amounts of phaeomelanin, the resulting skin will be black or brown. If you have low amounts of eumelanin but high amounts of phaeomelanin, the resulting skin will be light (freckles are likely too). People with very little levels (or none at all) of both eumelanin & phaeomelanin will have extremely light skin, this is known as albinism.

What about tanning? The more you expose skin to ultra-violet (UV) rays from the sun, the more melanin the skin produces. This will result in darkening the skin and helps to protect skin from any more damage. sun
Back in the day when most people huddled around the equator, they got a whole lot of sunlight and therefore a whole lot of vitamin D too (from the UV radiation).
We need vitamin D to help prevent illness such as rickets or soft bones so when people started moving away from the sun and dispersing to different, darker parts of the world, their bodies began to compensate for this loss of sunlight and the resulting loss of vitamin D. This happened by lower levels of melanin being produced and the lightening of skin, so more sunlight would be able to be absorbed. 

Hair

When it comes to hair, I barely know whether to describe mine as brown, blonde, muddy blonde, light brown? Sometimes I see strands of red and sometimes strands of black? It’s a bit of an identity crisis situation. 

You see, just like out skin, hair contains eumelanin (dark pigment) and phaeomelanin (light pigment). The density and the dispersal of the different types of melanin and their pigments will also contribute to differing hair colours, which can also happen across the space of one head. 

There is brown eumelanin and black eumelanin. 
If only a small amount of brown eumelanin is present, the resulting hair colour is blonde. Larger amounts of eumelanin will produce brown, dark brown and black hair. 
For red-heads, phaeomelanin is the dominant pigment which people with dark hair also sometimes produce. However, the darkness of their hair, thanks to eumelanin, overpowers the light pigment. In my case where I see hair strands that are red, light brown, and blonde, it is likely due to some phaeomelanin being produced. Grey hair is when only a small amount of melanin remains in the hair while white hair is the complete absence of melanin.

hair

There are so many variables in our hair, skin and eye colours and that makes a pretty cool world full of unique and interesting humans. We’ve heard it before, but really, if we all looked the same, the world would be a pretty boring place! 

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The building blocks of rocks

Today I want to talk about my first love, rocks.
I studied rocks for three years. I got to see rocks, hold rocks, scratch rocks, memorise rocks. Sometimes I got to go on field trips and look at really, really big rocks.

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Rocks are pretty great.

What’s also pretty great are the building blocks of rocks, minerals. 
Minerals are the natural crystalline structures found within rocks, and are used to interpret what kind of rock you’re looking at e.g. garnet, topaz, diamond.  They are solid structures made up of chemical bonds and there are around 4000 different kinds identified so far. Although it’s not generally the best way to identify a mineral as most minerals are white in their purest form, the colours of minerals can also be pretty exciting and draw people in. 

minerals

We learnt about wavelengths waaay back here and it’s the amount of absorption of these wavelengths which determines the colour of a mineral.

It is mostly atomic bonds within these minerals which do all the wavelength-absorbing.

Minerals consist of elements. For example, an extremely common mineral, quartz, has chemical composition SiO2 meaning it is composed of elements silicon (Si) and oxygen (O) bonded together.

LAtticestructure

A few elements contain electrons that like to absorb wavelengths as it is these wavelengths which provide them with a booster of energy – the amount of energy depends on which wavelength is absorbed. Bonding between different elements changes the amount of energy electrons have resulting in different colours. elements

Elements that can do this can have great influence over the colour of a mineral, even just the tiniest trace. It is also thought that almost any element could produce almost any colour.

Nickel (Ni) for example will taint minerals green as seen in annabergite

Uranium (U) will colour minerals yellow like in zippeite

Cobalt (Co) creates the violet/red colour in erythrite

Diagnosing a rock over the colours of the minerals can be pretty inaccurate. A more reliable test is that of streak. Finding the streak, or ‘powder colour’ of a mineral involves rubbing the mineral across a white, unglazed porcelain plate. The colour of the powder left on the plate is the streak. Up to 20% of minerals have streaks that are super useful in determining what mineral they are.

We can also describe rocks as mafic or felsic.
Mafic is the term used for rocks and minerals with high iron and magnesium content and generally give rocks a dark colour.
Felsic is used for rocks and minerals with high silica content and are generally light coloured. 

I loved my rocksstudies of rocks as they seem to have a story. Once you learnt the tricks, you can start to decipher the mysteries of what has happened to that rock. 
Finding diamonds in a rock tell you that it has been buried over 150km deep as diamonds only form under extremely high pressure. 
Finding halite (rock salt) is a indication of evaporation of fluid, possibly old brine lakes or seas. 

Next time you’re walking along a beach, have a little squizz at the rocks you see. If you look really close, you might be able to see little shiny different-coloured crystals of all sorts of different minerals which could end up telling you a really good story. 

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