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Friday, November 9, 2018

Greenland melting and Latent Heat

Possible effects of Latent Heat with regard to the melting of Greenland are interesting.  As usual, this is speculation but based on old established physics.  So what is Latent Heat.

When you add heat to an object it gets warmer.  We will use the old imperial measurement since in this instance it is easier to understand.

A calorie (with a small 'c') was defined as the amount of heat needed to raise one gram of water by one degree centigrade.  This is not Latent Heat. The term used is Sensibl Heat - possibly because we can sense when something gets warmer.  And, of course,  it will take 100 calories to raise one gram of water, starting at zero degrees to the boiling point.

There are two types of latent heat.  Lets start with the phase change from ice at zero degrees to water at zero degrees.  For this transformation, it takes 80 calories to melt one gram.  That is to say, the amount of heat to melt a gram of water is the same as is needed to raise that gram of water from 00to 80 degrees Centigrade.  This is the latent heat of the phase change between ice and water.

Importantly, when water becomes ice, exactly this amount of heat is given out.  You might be tempted to say - "but won't this heat up the water".  No.  But it will keep the temperature at zero degrees centigrade until the water is all frozen.  Similarly, when ice is melting (say in a styrofoam cup) it will remain at zero degrees until all the ice is melted at which time the added heat will cause the water to warm.

The second  latent heat is the phase change from water to water gas (water vapor).  To convert a gram of water to water vapor takes 540 calories.  This is 6.75 times as great as the phase change between ice and water.  This will be important below.

Let's see what the importance may be of latent heat with respect to the great big ice cube which is Greenland.

At some time in the not too distant future, all the ice will be gone on the Arctic ocean.  Initially it will only occur in mid September when the ice minimum occurs but the period of no-ice will widen in subsequent years.  Without ice, the heat absorbed by the open water will go into warming the water*.  Here is our first effect of Latent heat, in this case the Ice-Water Latent heat.  The ice will keep the water cold until it is all gone. When the ice is gone, the water begins to warm up.
Actually this is a bit of an exaggeration.  If you draw a cross section of the Arctic ocean to scale, it is a very shallow body of water in comparison to it's width.  Already, for a considerable portion of the melt season, large areas are ice free.  These are warming already since the ice that could keep them cool is far away across the ocean, but you get the idea.

As more and more of the water is ice free, we have ever warmer water on the surface of the Arctic ocean, heating the air from below and evaporating water vapor into the air.  Since the solar radiation penetrates into the water, the warming occurs over one or two tens of meters of the surface.  It takes a lot of heat to warm water so the temperature only gradually increases but a very large amount of heat is stored in this surface water.  It heats and humidifies the air blowing across the ocean.  What happens when this air blows across Greenland.

First we must define The Lapse Rate.  The Lapse Rate is the change in temperature if you take a body of air and increase it's altitude without the addition or removal of heat.  For reasons, I won't go into, as air expands, it cools.  Conversely as it is compressed, it warms.  You can feel the practical effect of this if you pump up your tire with one of those cylindrical hand operated air pumps that you hold near the flexible tube that connects with the tire and pump with the other hand.  The hand holding the tube gets hot.  

Lapse rate is 9.8 degrees per km of altitude.  That is to say, if I took a perfectly insulated balloon full of air and raised it up a kilometer, it would be 9.80C cooler at the top then when I started up.

 Little boy inflatingf bicycle tires : Stock Photo

It gets a tad more complicated when there is water vapor in the air (as there always is)

Now, for the sake of the argument let's assume that we have fully saturated air at 100C blowing onshore in Greenland.  The air hits the ice.  Look at the following table.  That 10 to the minus 3 kg/m cubed in the third column is their way of saying grams so a cubic meter of saturated air at 100c contains 9.39 grams of water in the form of water vapor.

Water Content
(oC)(oF)(10-3 kg/m3)(10-3 lb/ft3)
-25 -13 0.64 0.040
-20 -4 1.05 0.066
-15 5 1.58 0.099
-10 14 2.31 0.14
-5 23 3.37 0.21
0 32 4.89 0.31
5 41 6.82 0.43
10 50 9.39 0.59
15 59 12.8 0.8
20 68 17.3 1.07
30 86 30.4 1.9
40 104 51.1 3.2
50 122 83.0 5.2
60 140 130 8.1

This saturated air contacts the ice at 00C and the ice cools the air and causes water to condense out of the air.  Remember that as water vapor changes into water, it gives out 540 calories per gram of water.  Each gram of water condensed from the air gives out enough heat to melt six and three quarter grams of ice*.

*Incidentally if you want to read a dramatic account of a warm wind blowing across ice, read the book Plains of Passage by Jean Auel.  True it is a novel but Jean did her homework and reports what generations of glaciologist have observed.  It is somewhere around chapter 42 or 44.  I can't find my copy of the book.   

Let's back up a step. Where did this heat actually come from.  The wind blowing across the open water is picking up the water vapor from above the ocean.  Each gram of water that evaporates from the ocean takes this 540 calories from the water.  So the air is cooling the ocean and the heat is being contained in the air as latent heat.  If you have a wind that is blowing for some time from the water to the ice, a considerable amount of heat can be transferred.

You remember, I said that the top ten or twenty meters of water are heated by the sun.  As the surface water is cooled by the wind, it sinks and warm water comes to the surface.  If the water has been open for a good portion of the summer, there is a lot of heat available.

Note that sun shining on snow isn't very good at melting it.  Most of the radiation is reflected back to space without warming the snow.  Clear ice or ice with a pool of water on its surface is a little different.  The radiation penetrates but has to heat a considerable layer of ice up to zero degrees C before melting starts.  

A warm wind is something else again.  The heat is applied on the very surface of the ice and is constantly replenished from the sea.  If there is considerable water vapor in the wind, latent heat of condensing water vapor is added to the sensible heat of the wind. 
 Sea ice reflects as much as 85% of solar radiation hitting the surface, hence absorbing only 15%. Ocean water, by contrast, reflects only about 7% of solar radiation, absorbing 93%.

If this was dry wind blowing across  Greenland, it would only contribute sensible heat to the ice.  The air would cool both by contact with the ice and the expansion of air as it rose up the slope.  However with a high water vapor content, some of the latent heat of the condensing water vapor stays in the air.  

You remember, in our example we started with 100C, fully saturated air.  At a little over a km in altitude, it would have cooled to zero degrees and would stop melting the ice.  However some of the latent heat which is released as water vapor condenses into droplets (fog), the air will remain above zero degrees to a higher altitude, all the while melting the ice.

Of course the situation get's rapidly worse as the air becomes warmer than the 100 C we took as our example.  Have a look back at the table. 

While we are at it, there is another scenario that may be relevant to the story of a melting Greenland.  

Suppose there isn't much wind but Greenland is bathed in war moist air right to the top.  This air is light (relatively) due both to it's temperature and it's water vapor content.  That's right.  Humid air is lighter than dry air.  The reason is interesting and explained below.  It is in contact with the ice.  The ice cools this air and condenses out some of the water vapor making it heavier.  If the droplets of water stay in the air as fog, this exacerbates the effect.  This air now begins to flow down the slope as a density current.

You remember the lapse rate.  It works in the other direction too.  For every km that this air flows down the slope (vertical kilometer), it warms by 9.8 degrees C.  Of course, it doesn't actually warm.  It transfers this heat to the ice, melting it.  These are the the famous Piteraqs that are seen around the shores of Greenland.   

A body of air flowing from the very top of Greenland to the sea would warm almost 30 degrees if it didn't gain or loose heat.  This heat plus the latent heat of water vapor condensing on the ice is available to melt the ice.  We should see some rather extreme melting events in the future.

Relative density of gases  
Gases have some interesting properties.  The volume of a gas is inversely related to pressure (if you keep temperature constant).  That is to say, if you double the pressure, you half the volume.  The volume of a gas is directly related to temperature.  Not Centigrade but Kelvin temperature otherwise known as absolute temperature.  This is temperature measured from absolute zero.  If you increase the temperature of a liter of a gas, for instance, from zero degrees centigrade (2730K) to 100 degrees centigrade (3730K) then the volume will increase by 373/273 =  1.37liters.

Leaving all this aside, let's get on to the really interesting aspect of gases.  It turns out that a given volume of any gas at the same temperature and pressure contains the same number of particles.  I say particles rather than atoms since many gases exist as molecules of two atoms such as N2, O2 and H2.  This has an interesting implication.  If you know what gas you have, you can work out it's relative density to, for instance, air.

Now air is a combination of mainly Nitrogen and Oxygen.  An atom of Nitroge has an atomic weight of 14 so each N2 atom is 28.  Oxygen, similarly has an atomic weight of 32.  So air is approximately 30 (I should have done a weighted average but we are just illustrating the principle).  Water vapor consists of two hydrogen atoms and one oxygen atom so has a relative weight of 18.  Water vapor is only 18/30 = 3/5ths or 60% as dense as air.  Now we need one more property of gases.

When you put sugar into water it dissolves and  to some extent the sugar fits between the water molecules.  The volume of the sugar and the water is somewhat less than the volume of the water and the sugar added together.  Gases are not like this.  Each molecule occupies the same volume as any other molecule.  So if you add a tenth of a liter of water vapor to a liter of air (with no condensation, of course) you end up with 1.1 liter of gas.

You can see, therefore, that humid air which is a mix of water vapor (relative density 18) and air (relative density 30) is lighter than dry air.

All bets are off, of course, if the water vapor condenses into fog.  Now you have a suspension of water droplets in air and it is heavier than dry air.


Thursday, October 25, 2018

The End of the Ice Age

Sorry to rain on your parade but it ain't over.  We are still in the middle of an Ice Age.  It has been going on for about 2.8million years and is not over.  It is actually, if named  correctly, an epoch.  Namely the Pleistocene Epoch.  This Epoch is colloquially called the Ice Age.

During the Pleistocene Epoch (Ice Age)  there have been many icy periods (Glacials or glacial periods) and relatively ice free periods (Interglacials or Interglacial periods).  We are at present in the Holocene Interglacial and the previous one around 125,000 years ago was the Eemian Interglacial.  You could say that the Holocene Interglacial started 20,000 years ago since that was the peak of the previous Glaciation but melting really got underway a little less than 12,000 years ago so that is usually taken as the beginning of the Holocene Interglacial.

We should already be beginning our slide into the next Glacial period (not Ice Age - remember, we are still in an ice age) but the plow, rice paddies and the destruction of forests slowed our slide into the next galcial just long enough for the Industrial revolution to kick in and send us into a warming phase.  Read Plows, Plagues and Petroleum by Ruddiman for chapter and verse on the plow, plagues and rice paddies.  Despite early (6000 to 8000 years ago) human influence delaying our slide into the next glaciation, we apparently were just starting into the next glacial period when the industrial revolution reversed the trend.

The final straw in our slide into the next Glacial was the demise of the population of North America due to European diseases and the black death in the 'Old world'  Both resulted in forests regrowing and the suck down of Carbon dioxide just enough to start the accumulation of snow way up on the high lands of Baffin Island.  Apparently there is still a halo of dead lichens around this area where the expanding permanent ice and snow killed the lichen.  Green house gases then increased enough to reverse the accumulation of snow.

Some scientists are predicting that we are going into a sort of Maunder Minimum in which sun activity decreases.  No way, though, that this will reverse our warming.  We have put way too much Carbon dioxide into the atmosphere.

Our output of green house gases, by the by, long before the industrial revolution, is the explanation of why this interglacial has been so much more stable, weather wise, than previous interglacials.

With our output of Green House Gases and especially Carbon dioxide, we have put off the next glacial and with a little luck we may put it off until the next Interglacial.

However, we now have too much of a good thing and it is time to put carbon back into the soil, into trees and to stop adding more to our atmosphere.  We have the technology.  Any reasonably bright year 12 student could tell the politicians exactly what they should be doing but the politician won't listen.  They want to be elected next time and need the money from the vested interests to succeed.  Until we make it illegal for anyone to contribute anything to any politician for any reason whatsoever, we will be pushing the brown stuff uphill with a spoon.  Never was the old adage, Who Pays the Piper Calls the Tune more true.

One of the barriers to the use of renewable energy is it's unpredictability.  In the long term, you know more or less how much wind and sunshine you will get at any location but it comes in unpredictable booms and busts.  There are may fixes including notably,  demand balancing of our grids (electricity priced to reflect the extent of availability over  demand and devices that use electricity selectively when it is most available and hence least expensive).  However, a really good battery for stationary applications would go a long way to help.  Fortunately there is a technology in the wings, which could fill in the gaps left by other methods and systems.  It is the Vanadium Battery.

You might ask yourself, why I get so up tight over terminology - namely the misuse of the term Ice Age.    You will see in the popular literature and even in scientific papers, the use of the term Ice age to mean the glacial period between the present Holocene interglacial and the previous Eemian interglacial.  Why is this important.  We as humans are prone to lie to ourselves.  For instance, we note that the megafauna of North America disappeared when the Ice Age ended.  And we admit that man might have had something to do with it but it was probably climate change.  Nonsense.

First, as I said, we are still in an Ice age.   (The Pleistocene Epoch to be totally correct) so it hasn't ended.  But that is the least of the deception.  The Mega Fauna survived repeated cycles of glacials and interglacial and depending on how you define them, there have been between 30 and 50 such cycles within the present ice age (Pleistocene epoch).

No, the NA mega fauna disappeared at the end of the most recent Glacial period.  They survived quite happily the end of many previous Glacials and the subsequent interglacial and only the recent one caused their demise.  The only difference was the arrival of the first people who ate their way through these animals from one end of the Americas to the other.  If you don't think that primitive hunters could wipe out the mega fauna of the Americas, just look at the extinctions in Australia (50,000 years ago) and New Zealand (700 years ago) or in  any other  area when man first arrived.   Now we are finishing the job with habitat destruction.  Soon we will be alone in the world and then pooooof.   We are Gone Burgers. Evolution can begin again from whatever remnants remain.

The Anthropocene actually started at different times in different locations with the arrival of man.  So much for first people being the guardians of nature.  In actual fact, they eliminated any animal that they could hunt faster than it could reproduce. Now modern man is finishing the job.

Tuesday, September 11, 2018

The story of wheat

I have just purchases a grain mill to make my own flour and hence the interest in this fascinating story.

                 The Story of Wheat

In the 'old days' you would take your wheat to a miller, he would grind it and you would take it home to bake delicious nutritious bread. But there was a problem.  Wheat berries would last till the next harvest and beyond, but once you ground the flour you had to use it or refrigerate it.  The oil in the germ was spread through the flour, the wheat was no longer alive and over time, it went rancid..... so, in the summer, you ground only enough wheat at one time for at the most a month.
 Image result for image grist mills

Wheat  was full of essential minerals, vitamins and oils that mainly came from the germ* (80%) plus some nutrients and valuable bulk from the bran. In a minute you will see why I said "was".

*The germ is the little embryonic plant inside the grain.  It is only about 20% of the weight of the wheat seed (berry) but contains 80% of the nutrients.  It is most easily seen in a dicot like a bean.  Soak a bean in water overnight and then dissect it.  You will see the little embryonic plant between the two sides of the bean.

Since wheat was harvested in the fall with winter coming on, ground flour would last for quite a while before going rancid as long as you kept it cold.

The short slelf life of flour didn't please the business men who saw a great chance to make a profit.  They wanted to be able to buy large quantities of wheat from the farmers, mill it into flour and ship it far and wide.  Fortunately for them along came the roller mill.  This allowed the  germ to be sieved out of the flour and presto chango, you had a commercial commodity that would last without refrigeration for a very long time.
 Image result for image modern flour mill

This was the beginning of the end for wheat as the 'staff of life',

For some unfathomable reason, white flour was considered a great luxury so the millers also sieved out the bran.  Was this possibly promoted by them??.  Out went  the little nutritional value left in flour and to add insult to injury, they worked out a way to bleach the flour.  All that was left was the bleached endosperm.  The bran and the germ was fed to animals who were better fed than us.

In the third world, many folks once ground their own flour and some still do so wheat was still a vital part of their diet but we in the west have found a way to even muck that up.

In the 1960's along came Norman Borlaug.  He was a plant breeder and got the Nobel prize for his work in the 70's.  He realized that you could increase the yield of the wheat plant considerably by conventional breeding but that the stalk of the wheat plant would have to be shorter so that wind would not flatten the more heavily laden wheat plant.  He bred not only wheat but rice and other grains to produce vastly greater yields.  In some cases he tripled the yield of these vital food sources.  So what was the down side.

Yields per wheat plant were greatly increased but the nutrient content didn't keep pace.  In fact it stayed the same per wheat plant as before.  Because of this wheat and other grain contained as little as a third of the essential nutrients per kilogram as previous varieties.  Starvation was fended off (at least for a while) but people suffered from nutrient deficiency. 

As a side effect, it is estimated that with the cessation of famine in a number of third world countries, there are now 700m more people in the world than would have been the case without this agricultural revolution.

As Richard Dawkins said in  his book The Greatest Show on Earth,  "If there is ever a time of plenty, this very fact will automatically lead to an increase in population until the natural state of starvation and misery is restored."

There is a get out of jail card and if you want to see what it is, click here.  It is not relevant to this discussion.

Come forward to today.  Wheat berries last a very long time.  The wheat is alive (as you can see by sprouting some) and under good conditions will last for decades.  The farmer can use this to maximize his profit.  If he has a silo, he can augur his wheat into the silo and sell,  either when the price is right, or when the grain merchant or miller has space in his silo to take his wheat.  But there is a problem. 

Along with the wheat he can be putting insects and insect eggs attached to the grain into his silo.  So what does he do.  He dribbles a little organophosphate into the grain as it is augured into the silo.  The Active compound is Pirimiphos-methyl, often going under the brand name Actellic.  (There are many other products with the same active ingredient).

As one farmer told me, the grain merchant, not trusting the farmer, puts in a little more and the miller ditto.  This might have been tongue in cheek or perhaps not.

If you read the rap sheet on Pirimiphos-methyl, it talks about full body protection when using the product and one rap sheet suggested that if you have any choice, use something else.  That is how toxic this product is and it is put regularly into our wheat; a product that is not only the main ingredient of our bread but is in a vast array of other prepared products.  Do you ever get the impression that you know an awful lot of people with cancers.

Info on organophosphates says that besides being carcinogenic, they cause dizziness, nausia, loss of memory, nuralgia (whatever that is) and a raft of other symptoms.

What is sad is that the use of Actellic is completely unnecessary.  Enlightened farmers, and there are precious few of them, pump Carbon dioxide into their silos from the bottom.  It does the same thing.  Carbon dioxide is one and a half times as dense as air so by introducing it into the bottom of the silo, it pushes out the air.  Any aerobic organism dies.

It gets worse.  Many farmers roundup their grain fields shortly before harvest.  This has two purposes.  First it brings the grain to ripeness all at the same time.  The grain is not killed, only the plant. The second reason is to stop his harvester from plugging up with weeds.  Of course, if it is roundup-ready wheat, it is also rounduped during its growing phase.  (Does New Zealand import roundup ready wheat for milling??).

We now have two carcinogens in our wheat and hence in our food chain.  Note that roundup has not been proven to be carcinogenic to humans.  No ethics committee would agree to the necessary experiment!!! However it has been shown to be carcinogenic in animals.  As the lawyers say, I rest my case.

So wheat has  been bred to reduce nutrients, machined to further take out what was left, bleached (in the case of white flour) and now poisoned, all in the name of profits for the industrialists.  I wonder how many other products that we eat day in and day out have a similar story.  How many of these additives
work synergistically to cause cancers.  For that matter are people really gluten intolerant or are some of them simply showing a reaction to the poisons they are ingesting.

Friday, August 24, 2018

Grinding your own flour, Making your own bread

I'm away from home just now but when I return at the end of the month (7/18) there should be a flour grinder waiting for me.  I suspect I will be making updates to this blog for years as I discover the joys of producing and using my own flour.  What have I discovered so far.

Apparently threshed and winnowed wheat berries (grain) will last for decades if kept, even at room temperature, as long as they are kept dry.  I remember something I read many years ago.  Somewhere, I can't remember where, there are some people that make grain storage bins from ferro-cement, buried in the ground with the removed soil making a berm around the entrance.  The bins are conical in shape getting wider toward the bottom.  Grain is alive.  It uses Oxygen and produces Carbon dioxide.  Apparently when the grain is stored this way, any insects, mice and anything that needs oxygen to survive dies.  The grain is preserved this way for very long periods.

Some "modern" folks apparently use a plastic liner for the grain.  Critical is to have the grain below 14% moisture for long preservation.  

In contrast, when grain is ground, it's shelf life is very short unless refrigerated and even then should be used in a week or so.  This is why the flour you buy at the store, even the brown flour, doesn't hold a patch on real whole meal flour for nutrition.  When you used to take your wheat for grinding to the mill, bread really was the staff of life.  However, in order to turn flour into a marketable commodity that would last, the germ had to be removed.

 This is the little wheat plant that is tucked into the grain and while it is about 20% of the weight of the wheat berry, it contains some 80% of the nutrients.  Using roller mills it was possible to remove the germ and make a flour that would last for a very long time and could be shipped long distances.  However, as with so much of our food, we lost a huge amount by having this convenience.

By the way, if you want to see the germ (the little plant in a seed), it is most easily seen in  a bean seed.  A bean is a dicot which means that the endosperm is stored in two halves and they can be split to expose the germ.  Soak a bean seed in water over night.  In  the morning, carefully remove the outer coat and split the two halves apart.  You will see the little plant inbetween.  You can even leave the bean in water that only partially covers it and let it sprout.  The little plant grows and can be more easily seen as can the cotyledons.  It is harder to do this with wheat but the principle is the same.

I have my grinder but before I get into it's use, I must tell you some more I have discovered about our wheat supply.  It is not pretty.

I have checked with a number of farmers and a grain merchant and the story remained the same with all of them.  Apparently when grain is augured into the silos, a little Pirimiphosmethyl is added against insect pests.  This can be added by the farmer, especially if he is going to store his wheat in his own silos for any length of time, by the grain merchant and/or the miller.  If you look up the rap sheet on this chemical, you find a recommendation that if you have any other choice of pesticide, use it.  This stuff is nasty. Besides being highly poisonous (you guessed it) it is a carcinogen. It gets worse.

If the weeds have got away from the farmer toward harvest time and even earlier if the farmer is using 'roundup ready' wheat.  he will roundup his field.  Apparently the weeds will plug up his combine so he lets the roundup do its work and then harvests.

So, not only do we have a known carcinogen pesticide in our wheat but a known carcinogenic herbicide.  Roundup has not been proven to be a carcinogen to humans.  After all, you can't feed Roundup to a hundred humans and not to a control group.  But it has been proven to be carcinogenic to animals. I rest my case.

What is particularly annoying is that the use of the pesticide is so unnecessary.  Enlightened farmers (and there are precious few of these) use Carbon dioxide.  They have a connection at the bottom of their silo where they can attach a hose from a Carbon dioxide cylinder and fill the silo with this completely harmless gas.  Problem solved.  Any insect or their eggs that have come in with the grain dies.

Sunday, June 10, 2018

Our white skin

We "whites" seem inordinately proud of our white skins.  We have always considered it to be a sign that we are superior to the darker variety of homo sapian.  So I thought it would be fun to consider where our white skin came from.

We all know that people living in sunny climates which includes much of Africa, where we originated, have dark skins.  Undoubtedly, this included all the species of the genus Homo that preceded us.  Look at our nearest relatives, the Chimpanzies and great apes.  All with black skins despite the fact that they live, for the most part, in jungles.  Early hominids must have spent many hours in the sun and often, due to warm temperatures,  went with limited body covering.  They had to spend considerable time in the open finding their daily crust of bread and they developed dark skins to protect their skin from too much sunshine.
 Image result for image chimpanzees

Note that the babies have white faces while the adult is black.  Why do you think this might be.

Sunshine of course, provides us with vitamin D which is essential for the calcification of strong bones.  A hominid with weak fragile bones hasn't got much of a show in an environment in which his speed agility and strength will often make the difference between eating or being eaten.

But, vitamin D is important for so much more and we keep finding additional functions  of this important vitamin.  Some functions which have so far being discovered include:

*Strengthened immune system
*Enhanced muscle function.
*Improved lung health
*Anti-inflamatory properties
*Reduced blood pressure
*Reduced hardening of the arteries
*Protection from kidney disease
*Suppression of a pathogenic appetite
*Protection agianst Alzheimer

So there is a strong selective pressure for anything that ensures you obtain enough vitamin D

Sunshine is not the only source of vitamin D either.  Other sources include:
*Fresh fatty fish
*Oysters and some other 'shell fish'
*Some livers
*Egg yokes
*Raw milk
*Some mushrooms
*Some fish eggs.

Think of the dilemma of the first hominids that left sunny Africa.  Those that migrated along the coast toward India had little selective pressure to evolve a light colored skin.  Not only did they migrate through sunny climates but if they were able to fish, they would have got their vitamin D that way.

However for those that left the beach and migrated northward it was a different story.  There was a double whammy against them.  First, if they migrated into northern climates, it was more cloudy giving them less exposure to sun.  In addition in these colder climates, they would have had to dress in skins or clothes made of wool which was shed annually by various woolly animals.  They probably had only their face and hands exposed to the sun so there was a strong selective pressure to loose their protective melanin so that they could obtain their vitamin D.

For the males, there was another factor.  We had beards, possibly for the same reason that a male peacock has beautiful feathers so even less of our skin was exposed to the sun.

The interior of continents are very warm in the summer so they probably also evolved the ability to sun tan, if they didn't have this already.

According  to our present archaeological knowledge, Homo erectus  arrived in Eurasia at least 1.6million years ago.  For those that challenged the northern interior of the continent, there would have been a strong selective pressure for the evolution of a white skin.  Erectus sites from 1.6m years ago contain  flint tools including  retouched flakes so he was no dummy and it is not unreasonable to assume he fashioned some sort of covering.

Homo erectus likely evolved into  Homo heidelbergensis and then into
Homo neanderthalensis.  It is unlikely that this was a new migration from Africa since neanderthal genes are found in European people of today but not in modern Africans.  Incidentally another species which may have developed from Homo erectus is Homo sapiens denisova  further East in Asia.  Presumably, Denisovians who lived in northern climates characterized by cold cloudy conditions, they also had pale skins.

But there is something curious.  Bones of Homo sapien have been found in Africa from 315,000 years ago but only appeared in the fossil record in Europe 45,000 years ago.  How come.  Of the various theories presented, my favorite is armament.  It is likely that Neanderthals and our species came into contact much earlier than 45,000 years ago in the bridge from Africa to Europe, namely in the middle East. Think what a conflict that would have been.  The gracile Homo sapien comes up against the powerful, robust Homo neanderthalensis who makes his living stabbing large and small animals at close quarters with his spear.  No prizes for working out who would win that contra-ton.

I suspect the critial development which allowed our species to make inroads into Eurasia was the development of throwing weapons.  This could have included the lance, atyl atyl*, sling and even the bow and arrow

*Trowing stick which allowed a spear of a size between a lance and an arrow to be thrown with much more force that with the hand alone.

Our whole history is one of killing at greater and greater distances*.  It has culminated now with cowardly soldiers sitting safely in America, killing people with gattling guns and hell fire missils from their drones in other peoples countries as if they were in some sort of video game.

*In more modern times, the Battle of Agincourt

Neanderthals were at two disadvantages.  Their culture was one of killing prey close up and with humans the way we are, there was probably a strong sexual selection for the man that did this most effectively.  You bring home the bacon and the girls want you for their mate. So their whole culture favored the man who was a real man and could kill a deer at close quarters. But they had a second disadvantage.

You would think that they would rapidly adapt throwing weapons once they saw how effective they were.  Unfortunately, through evolution, they had evolved a shoulder joint that while it was very powerful, it was not adapted for throwing.  Even if they wanted to adopt the new weapons, they would have been very clumsy at it. Neanderthals lacked a throwing arm.

An effective throwing weapon would have completely changed the balance of power. And again, the way we are, when a tribe of Sapiens defeated a tribe of Neanderthals, they probably killed all the males and took the females for themselves.  Here a little diversion into genetics.

With the difficulty of travel when all you could call upon were your legs, and considering how territorial humans are, the two tribes were what we might consider pure breeds.  In other words, they would have had a high degree of homozygosity* at many more sites on their chromosomes than modern humans who breed with other humans who are distant both in geographical terms and in their genetics.

*Each cell of our bodies has two copies of each chromosome.  The genes on each chromosome at the same locus can be the same (homozygose) or different (hetrozygose).  When closer related individuals mate, this increases homozygosity and of course when a recessive lethal gene or even a disadvantagous gene comes together in an individual, he is either dead or disabled.  Inbreeding over time, to some extent, weeds out deleterious recessive genes from the population.  When two inbred individuals from different genetic lines breed, their offspring are likely to be particularly robust

 We keep chickens for the production of eggs.  We start with a variety called brown shafers who are great layers.  They are a hybrid of at least 4 so called pure breed varieties and express hybrid vigor. However we allow them to breed freely and you should see the varieties of chickens produced.  They not only revert to the original varieties but produce all sorts of assorted mixes.

Imagine the offspring of this first mating of male Sapien with female Neanderthals.  The two populations had been isolated and inbreeding for thousands of years.  The result would have been the equivalent of our Brown Shafers.  They would have all looked very similar and likely would have been very strong with a somewhat better throwing arm than Neanderthals but not a good as Sapien and with an intermediate skin colour.

In order not to make the whole story too complicated, I will assume that a throwing shoulder is determined by one gene and likewise skin color.  Any genetisist will tell you that many genes are involved in the determination of these characteristics and most others.  Mendel lucked on to some characteristics of peas that indeed were determined by one gene and so laid the basis of genetics.  I will also assume that both genes have equal influence.  That is neither is dominant over the other.  We will use W for a white skin and w for a dark skin.  Also T for a throwing shoulder and t for a non throwing shoulder.  This is a huge simplification but will make the situation easier to understand.

In what the genetisists call the F1 generation we have a cross between two quite homozygous populations (pure bred) The offspring will have half their genes from the mom  and half from the dad and those from all the dads will be quite similar to each other and likewise all those from the moms, similar to other moms.  Then the fun starts.

When the children start to reproduce, their offspring will have all sorts of mixes of these genes.  We will have:
WWTT - a white skin and a throwing shoulder
WwTT - a dusky skin and a throwing shoulder
wwTT - a dark skin and a throwing shoulder
and so forth.  Use a Mendelian square to work out all the variations.  On one axis you put WT, Wt, wT and wt and the same on the other axis.  These are the genes in the gametes (eggs and sperm).  Now selection begins.  Since humans are nasty and of great danger to each other, a throwing shoulder will be selected for as will a lighter skin, especially as these hybrid humans move away from the coast into more northern areas.

We have all heard by now that we have a small percent of Neanderthal genes.  This begs the question of what is a species.  The old definition was that two individuals are of the same species if they can produce a viable offspring that itself can breed and produce viable offspring.  Of course the situation on the ground is more complicated than this.  Apparently the various species of hominin in Africa bred back and forth in all sorts of combinations and clearly we bred with Neanderthals.  Otherwise we wouldn't have their genes.  Over the thousands of years since we started to breed with Neanderthals, individuals would be selected with characteristics from both strains of human that had the best survival.  Here we have only considered two.

I suppose we we were lucky to breed with a species that had already adapted to northern climates.  It would have speeded up considerably our rate of adaptation as we kept those characteristics that benefited us rather than having to start with favorable mutations - a much slower process.

We can thank the Neanderthals for our white skin.

Post scriptum
Facts are such a bitch when it comes to a great theory.  It was great fun poking fun at the white supremicists but it turns out that it probably is not true.  Have a look at the youtube videos from this chap.   Apparently it is true that at least some neanderthals were white and interestingly they had red hair.  The whatsit in the woodpile is that the genes that make present day whites, white are different from the ones that made Neanderthals white.  We seem to have evolved out own genes to turn our skin white and hence give us our daily dose of Vitamin D.

Now, of course, this doesn't mean necessarily that all Neanderthals were white.  If there was a population that lived in sunny parts of the world or on the sea shore where they got enough vitamin D from the sea, they could well have been black or brown, just as present populations of humans display all color variations.  Anyway, so much for a fun theory.