Why Do Fingers go Wrinkly in Water?

November 3, 2015 / Humans / 0 Comments /
Header image for wrinkly fingers

Most people will have noticed that if you stay in a body of water for any extended period of time, your fingertips will go wrinkly. You may have even noticed your toes doing the same, but it doesn’t happen anywhere else on your body – ever wondered why?

Originally, it was thought our fingers went wrinkly because the outer layer of skin (which is made up of dead cells) absorbed water when we were submerged in water for any length of time. The absorbing of water like this would increase the volume of the outer layer of skin, but its can’t just expand out as a sponge would, because it is firmly attached to the underlying layers of skin. So, instead it would wrinkle, which increases its surface area and allows for the expanding surface layer. However, this is not the case.


Improved grip

When we are submersed in a body of water for any length of time, nerves in our fingertips trigger vasoconstriction. It is possible that the nerves are triggered by the water being absorbed by the outer layer of skin, but we don’t know for sure.

This vasoconstriction reduces the volume of the padding in finger tips and toes. You can feel this padding simply by gently pressing your finger tips with other fingers. This padding is essential for our fingers and toes and offers protection for everyday scrapes.The surface area of the finger tips stays the same, so when the volume decreases, the skin wrinkles. It is the same thing that happens to fruit when you dehydrate it. A grape is nice a smooth all around, like our plump little finger tips, but if you dehydrate a grape, it turns into a wrinkly little raisin. This is because all of the water, which makes up most of the volume in the grape has gone, and so the skin is forces to go wrinkly.

This is quite an interesting thing to happen – rather than it being an involuntary thing that just happens when we go into water, the body actively causes this to happen, which suggests there is a reason…..

And there is! Research has shown that wrinkly fingertips are very good at gripping wet objects, and they do this because the wrinkles create channels that allow water to drain away as we press our fingertips on to wet surfaces. This allows the fingers to make greater contact with a wet surface, giving them a better grip. 

Being able to grip wet things in water has a clear advantage – it will allow is to climb out of water easier, hold weapons easier, or even keep hold of wriggling food we have just caught.



So, getting wrinkly fingers when we are in the water is not some bizarre result of our skin absorbing water, but rather, it is a very clever evolutionary trait which allows us to grip things better when wet. It is a fascinating evolutionary adaptation, and not one anyone would have thought about. For this small adaptation to be significant, you would think that we would have evolved in a much more aquatic environment than deep inland, and perhaps this offers a small insight into how our evolutionary ancestors lived – perhaps we evolved on or around the coast after all….

Image courtesy of Nicole Hanusek

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Blood vessels constrict, which reduces the volume of the padding in our fingers, which causes them to wrinkle. The reason for this adaptation seems to be to improve our grip on wet objects.

Why is the Sea Salty?

September 16, 2015 / The world around us / 0 Comments /
Why is the sea salty

Although fresh water runs into the sea, the sea is salty. Its strange really, and so in this article I’ll explain why the sea is salty.


Minerals in the Earth’s crust

The ground is not just inert dirt and rocks – it contains an abundance of chemicals and minerals. Amongst all these minerals is sodium, which is the the 6th most abundant mineral found in the crust. Sodium is most commonly found bonded to less abundant (but still relatively plentiful) chlorine, which forms sodium chloride – what we call table salt. Salt is water soluble, and so when it rains, the salt in the ground dissolves in the rain water and runs into the rivers, and ultimately into the seas.

When the water in the sea heats up from the sun it evaporates and forms clouds, but the salt is far to heavy to evaporate with the water, and so stays in the seas.

This process continues over many many years, and the weather/ rain will break rocks up/ wear rocks down, which exposes more mineral rich rocks/ soil, which rain water will also dissolve and wash into the sea.

This process concentrates salts and other minerals in the sea, because the salt cannot escape, but the water can through evaporate. Gradually this builds up the salinity of the seas to the point where the seas are significantly saltier than water in the rivers which feeds them.


Other causes

When underwater volcanoes erupt they release a number of chemicals into the seas and oceans which were previously trapped in the crust below the ocean floor. Amongst these chemicals will be sodium chloride (salt), which will further contribute to the salinity of the sea, but to a much lesser extent than the rivers do.


What about other minerals

With sodium only being the 6th most abundant mineral in the crust, and chlorine being even less abundant, you might wonder why the sea is salty and not another kind of flavour (minerally?). Indeed aluminium, calcium and iron are far more abundant that chlorine and sodium, so you might expect the sea to be more abundant in these minerals than sodium and chlorine.

Iron  – Iron is nearly 5% of the crust, which makes it almost twice as abundant as sodium, and it is in fact the most abundant element on the planet. Very little iron reaches the sea e sea because when water comes into contact with iron it readily forms a compound called iron oxide (which we know as rust). Iron oxides are not soluble, and so don’t easily run off into the seaA graph showing the relative abundance of minerals in sea water

Aluminium – Aluminium is nearly three times as abundant as sodium is, but very little is found in the sea for the same reason as iron. Aluminium reacts with oxygen far too quickly, and becomes insoluble too.

Calcium – Calcium is usually found in the crust in the form of calcium carbonate, which is very stable and so doesn’t dissolve very well in the rain water. Calcium compounds do dissolve in water to some extent though and do make it to the sea, which makes calcium one of the more abundant minerals in the sea.

Other minerals are present in the water, the most notable of which is potassium and magnesium, which are moderately abundant in the crust, but due to solubility, are found in higher concentrations in the sea.

Interestingly, it is the presence of these additional minerals which makes using sea salt to season food a healthier option than regular table salt.



The sea is salty because rain water continuously washes salt from the rocks/ soil on land into the sea. The salt cannot escape because the salt atoms are too heavy to evaporate with the water the dissolved in.

Despite not being the most abundant minerals in the sea both sodium and chloride ions are water soluble, and so will readily wash into the sea where other more abundant elements won’t. This is why sodium and chloride concentrations are higher in the sea than in the crust.

Image courtesy of ninfaj

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Over millions of years salt from the land has been dissolved and washed into the sea by rain water. As salt it heavy, it cannot evaporate, and so stary in the sea.

How Long Can You Live Without Water?

July 30, 2015 / Humans / 1 Comment /
How long can humans survive without water article

A similar question to ‘how long can you live without food‘, but with some key differences. Your body is able to store energy to some extent as fat, meaning some people can survive without food longer than others. The body cannot store water, so the answer to how long you can survive without water will be much more accurate and consistent. So, assuming you, right now, a perfectly well hydrated person with clear urine is no longer allowed water, how long would you survive?


How Long Can You Live Without Water

I’m going to make some reasonable assumptions to make this easier – you are in a moderate climate so won’t be sweating excessively, you are well fed and hydrated for, you won’t be doing any exercise and you are not elderly or an infant. Essentially, if you will be doing nothing which causes you to lose excess water.Humans can survive 3-4 days without water.

Well, unsurprisingly there is no specific research for this, because it would be very cruel (not to mention illegal) to do this kind of research. In fact, most researchers agree that there is too little known about how much water we need and what our requirements look like.

The best answer I can get from a scientific body is the complete absence of water ‘will be lethal in a few days‘, which anyone could have guessed, and is quite vague. Further digging around and I’ve found that the general consensus is that you can only live 3-4 days without water before you die. In hotter climates, or if you are exercising, this could be as low as 1-2 days, but it depends on the climate and the exercise you are doing. In normal conditions which I described above, it is 3-4 days. However, you won’t just feel normal and then drop dead, you will steadily feel worse and worse as you go through the stages of dehydration.


Stage of dehydration

Early stages of dehydration

Most people will be familiar with the symptoms of early dehydration, and they are easily reversible but drinking some water. These usually will kick in a few hours after drinking when your body has lost roughly 2% of its total fluid. These symptoms are:

  • Dry mouth
  • Thirst
  • Dark urine
  • Tiredness


Moderate dehydration

Symptoms of moderate dehydration will kick in when you have lost about 5% of your fluid, and these symptoms will probably develop over day 2-3. These symptoms are:

  • Increased heart rate
  • Muscle cramps
  • Tingling/ numbness in limbs and extremities
  • Extreme tiredness and poor physical performance
  • Fuzzy thinking and dizziness


Late dehydration

The symptoms of late stage dehydration will occur when you have lost about 10% of your fluid, and will start to develop through days 3 and 4 without water. The symptoms are:

  • Painful urination
  • Muscle spasms
  • Loss of ability to think straight
  • Loss of consciousness
  • erratic heart beat
  • ….then death


How do humans die from dehydration?

It would be great if water wasn’t so essential to body functions, maybe then we could survive longer without it. Sadly, water is needed for pretty much every that goes on in the body. One of the first signs of dehydration is dark urine, and this is because water is needed to transport waste chemicals such as urea out of the body. As water gets lost through urination, respiration and perspiration, the amount that the body can afford to lose decreases, meaning more is lost through urination, which is the greatest cause for water loss. This is far from fatal though.

If dehydration continues, less and less water will be filtered out of the blood as urine, which can put a lot of strain on kidneys. Your blood volume will also decrease because water is a major component of blood. This reduced volume puts strain on the circulatory system, particularly the heart, which increases heart rate to try and compensate for the loss of water. The reduced volume also causes the blood to becomes thicker, which leads to difficulty in providing nutrients to parts of the body, which can cause tiredness, tingling in extremities and poor physical performance. Also, as a healthy brain is about 73% water, the brain will start to become dehydrated, which can cause fuzzy thinking. You may recognise all these symptoms are part of moderate dehydration, and although it’s not fatal just yet, you can start to see that functions in the body are struggling.

Breathing also increases to try and compensate for the reduced blood volume,, and usually the body temperature will rise due to reduced sweating.

As dehydration continues even further, important biological systems start to break down completely. The volume of the blood becomes even lower, putting even more strain on the heart, and even the heart is struggling to get enough water for it to function properly. This will become too much for the heart and will lead to nutrients not reaching muscles in limbs, which can cause muscle spasms. More and more water will be lost from the brain, which will further affect thinking, and ultimately cause unconsciousness. Eventually, the heart will no longer be able to function, and is usually the cause of death from dehydration.


Summary – How long can you live without water

Although there is not a great deal of research into this, it is generally accepted that you can’t survive more than 3-4 days without water. During this period, many biological functions will start to fail, but the cause of death from dehydration will be heart failure.


Image courtesy of John ‘K’

Can Saturn Float on Water?

July 9, 2015 / Space / 0 Comments /
Can Saturn float on water?

A common physics factoid is that Saturn will float in water. This is because Saturn has a density of 687.00 kg/m³ and water has a density of 999.97 kg/m³. As Saturn has a lower density than water, it should float. This works with objects like ice cubes, which also have a lower density than water, so float. It makes sense on the surface, but scaling this up to planetary sizes makes make things behave differently. After spending some time reading about it, I’ve found that despite having a lower density than water, Saturn wouldn’t actually float, and here is why.


Why Saturn wouldn’t float

First of all, Saturn couldn’t float anywhere on Earth because there isn’t a body of water big enough on Earth for it. If you imagine an iceberg in the ocean, or an ice cube in a glass, a small amount sticks up above the water, and there is a massive amount below. Saturn would behave the same, but Saturn is so big that there isn’t a body of water on Earth big enough to accommodate the bit of Saturn below the water. So, first of all, we would need to find a planet which would hold a body of water deep enough.

Fortunately the guys over a Wired have done this calculation for me (so you can check their maths), but they say you would need a body of water as deep as 6x the Earth (sounds massive, but remember that Saturn is nearly 10 times bigger than the Earth – its huge!).

So if we assume we find a massive planet which can support this much water, we still have another problem. Having a body of water as deep as 6 Earths is going to put the water at the very bottom under an immense amount of pressure -much much more than can be replicated in a lab. What water would do under all this pressure is a mystery. The amount of pressure is massive its hard to comprehend, but I’ll try and give you some sense of scale. The depth of water would be about 7600km, and the deepest part of the ocean on Earth is the Mariana Trench, which is only 11km deep.

Usually under large amounts of pressure liquids would become solid, but water is unique in that its solid state floats on its liquid state, and this is much more pressure than is required to just chance a liquid to a solid. Its unknown what would happen to water under all this pressure, but I have come across a number of theories, some say you would end up with a superheated liquid with a reduced volume and others suggest you would end up with something called electron-degenerate matter, which from what I can tell, will probably result in a star forming – quite dramatic.

Either way, all theories suggest that the conditions created would be extremely unstable, and so unlikely to allow a gaseous giant to float on them. What’s more likely is that  the chemicals which make up Saturn (which are largely hydrogen) would also undergo fusion reactions and contribute to the forming star.

Finally, if you manage to overcome the very real problem above, there is one more issue. Like our planet, Saturn has a core which is made up of liquid metal and rock, neither of which would float on water. In fact, most of Saturn is gas, mostly hydrogen, and so if you were to bring it onto a planet which could support a big enough body of water to support Saturn, the gravitational pull would probably disintegrate the gas, and the core would sink to the bottom of water – not float.


Summary – can saturn float on water?

It might seem like Saturn would float on water because it has a lower density than water does, however, in practice, it will probably be a very different story.

First of all, the sheer volume of water that is needed would create a very unstable and reactive environment, which potentially could cause a star to form, which would probably destroy Saturn rather than keep it afloat.

Secondly, if you somehow solve the problem of the first point, the core of Saturn would fall to the bottom of the water, and the gas would probably disband – again, not really floating.

It really is a theoretical nightmare, and not something that my Physics A level really equipped me to solve, but it does seem very unlikely that Saturn would float in water.

Images courtesy of Robbert van der Steeg and Patrick Rasenberg

This Youtube video will give an overview of the information found on the article tab. If you want to know more about the topic, or want to see where the information came from, have a read of the article after you watch the video.

No – the conditions are impossible. There is more to consider than just density.