Everyday use of the Scientific Method

About a year ago I had an experience of how the scientific method could apply to a simple domestic situation. I thought I would share it as there are parallels between science and pseudoscience in this story of everyday folk.

I rented a house in Lincoln (UK) whilst I was an academic at the University’s School of Pharmacy. An electric immersion heater supplied hot water and that tank was kept full via a standard ball-cock valve on the cold water supply. All was not well with the hot water supply however, because there was a constant trickle of cold water into the tank irrespective of hot-water usage.


A lot of scientific discovery starts with pure curiosity, the “that’s interesting, I wonder what that is?” type question. A good example of this was when Richard Jorgensen became curious about patches of colour on petunia petals. His investigations led to the discovery of a whole new branch of genetics and won him the Nobel Prize in 2006.


Although I was not about to win a Nobel Prize, the constant trickle of water was nevertheless intriguing. I therefore formed a hypothesis that there was a leak somewhere in a hot water pipe. I traced all the pipework to see if I could find a telltale pool of water. There was none and hence no evidence for a leak.

Perhaps I was misinterpreting things and the constant trickle of water into the tank was normal. But the investigation at that point was superficial and so I investigated further. I found the main valve feeding the tank’s cold water supply and turned it off overnight. The next morning the tank was empty, so where had the water gone? I found the valve for the tank’s hot water outflow which I turned off and the constant trickle of inflowing cold water stopped. With both the cold water feed valve and hot water outflow valve off, the tank remained full. Clearly that constant trickle of water was not normal.

With no visible signs of a water leak, the tank was still emptying in a matter of hours. Perhaps the water was leaking somewhere I couldn’t see? I knew one hot water pipe went under the floor to feed the kitchen tap. It was a concrete floor and so I couldn’t get to the pipe to observe if there was a leak or not.

Make predictions from the hypothesis and test them

Scientists figure things out all the time without making direct observations. Instead they look at the consequences that a particular hypothesis might have and then work out what’s happening from there. In my case, there were no valves to isolate the under-floor pipes and so I had to get a little more inventive. The underfloor pipe branched off from the main pipe at a T-junction. One end of the T went to the kitchen tap (under the floor) the other went into the bathroom. So I came up with an idea that involved the flow of heat, rather than water.

The house had copper pipes which are good conductors of heat. By opening or closing the kitchen and bathroom taps, I followed the flow of water simply by feeling the heat running along the pipes. In technical terms, the heat was a surrogate for the water flow. With the bathroom and kitchen taps off there should be no flow of hot water and therefore all pipes should remain cold. Over time however, the pipe that went under the floor became warm, while other pipes remained cold. The conclusion was that there was a flow of hot water (detected from the heat of the pipe) under the floor, even when there should be none. The most likely explanation therefore, was that the pipe was leaking somewhere along its length under the floor.

Hypothesis becomes a theory

On the weight of evidence, there was a leak in the hot water pipe under the concrete kitchen floor. The evidence was consistent with the known laws of physics – for example, water flows downwards under gravity, copper conducts heat etc. In science, a theory has to be consistent with what is already known. For example, if some theory of biology breaks a law of physics, then the biological-theory cannot be right. Science is joined up in that way, each part has to fit with all the other parts. Pseudoscience on the other hand has no problem believing all the textbooks can be re-written just to accommodate their particular ideas. Getting back to my leaking pipe, it was time to call the landlord and get a plumber.

I explained my diagnosis to the plumber but he did not like the outcome. I could tell that the thought of having to uproot the floor did not appeal to him. He therefore said he would replace the ball-cock valve, which he claimed must be leaking, causing a constant trickle of water.

Counter hypothesis

I explained to the plumber how changing the ball-cock valve was not consistent with the evidence. How, for example, did the hot water tank empty when the ball-cock valve was isolated by turning off the main cold water tap? But he didn’t want to hear it. He told me he’d been a plumber for 20 years and so he knew what he was doing. An appeal to authority however, was not consistence with the actual evidence. The problem was that he didn’t want to accept where the evidence was leading simply because of the personal consequences to himself. Science frequently encounters such self-motivated objections. The economic consequences of reducing carbon dioxide emissions, for example, are so profound that the theory of climate change must be wrong!

Getting back to the reluctant plumber, after a little discussion, I got him thinking and he said he would check something out.

Independent testing of the theory

He went outside the house and dug down by the wall next to the kitchen. It didn’t take long before he hit mud. What he was hoping for was dry soil which would be counter-evidence for a water leak. In fact, dry soil under these circumstances would not have been particularly diagnostic one way or the other because the leaking water could have been flowing in any direction under the house. In science, some evidence is robust and other evidence is more circumstantial. It’s a common fallacy to confuse the two as being equal. The wet ground in this case, was supporting evidence for the leak-theory but the plumber then rationalised the mud by saying it had been a wet year and it could just be ground water.

Unsinkable rubber duck!

This is a term used by rational thinkers when someone finds a way round every item of evidence presented to them to support their own preconceived position. Young earth creationists who believe the earth is less than 10,000 years old are masters of the unsinkable rubber duck. Point out that light from distant stars has taken many millions of years to reach the earth, then they will claim the speed of light has not always been what it is today. Likewise, no matter what the outcome from the plumber’s test-dig by the kitchen wall, it would reinforce his own viewpoint or at least not change it. But I had to be careful because although the mud seemed to support my leak theory, the possibility that is was a coincidental ground water could not be ruled out as there could have been multiple reasons for this observation. Scientifically, I could have added a tracer dye to the hot water to see if it ended up in the mud. Even for me however, this seemed a little over-the-top and so instead, I suggested that he dig another test hole around the other side of the house to see if that was wet due to the water table. He thought about it but declined. To him, unwillingness to further test his theory seemed to reinforce his own position.

Confirmation of the theory. In science my water leak would have been tested in a multitude of ways. Someone may have come up with some new ingenious methods and others would have confirmed or failed to reproduce my data. Then those tests repeated and so on, with the results either reinforcing the theory, leading to modifications of the theory or even to discard it and start again. Pseudoscientists on the other hand are content to accept the first whiff of flimsy evidence that might vaguely support their point of view and ignore far more robust evidence against them. The case of my hot water was a little more domestic and anyway, showering at work was getting tedious.

So what happened? The plumber and I did not pass on particularly good terms. I got on well with the landlord and so he let me find another plumber for a second opinion. The second plumber wasn’t that bothered about my method of diagnosis as he saw a simple solution. He simply put in a new pipe above floor level, bypassing the one with the leak. He took about an hour and afterwards the problem was solved. The constant trickle of water to the tank stopped.

In science, this would have opened other questions such as, exactly where was the leak and what was the cause? Even without knowing this level of detail however, the theory of an underfloor leak in a hot water pipe still stood firm. In contrast, pseudoscience often presents any gap in knowledge as evidence that the whole theory is wrong. You don’t know exactly where the pipe was leaking, therefore that was not the cause. You can’t observe every intermediate species between Hypohippus and the modern horse, so evolutionary biology must be wrong. Or the gap is filled with any old nonsense; aliens living under my house were stealing the water – that type of thing. Well, you can’t disprove it, can you?

And just a final note. My persistence with the first plumber was not about being right, it was about the evidence. All too often there are those who evoke the name of science to prove themselves right at any cost. Science is the exact opposite of this. Regarding the first plumber, if he could find better evidence to support a different theory then I would have been very pleased to change my point of view. Even if an alien had suddenly appeared out of the test-hole!

Elemental Beings (the mythical story of the discovery of radioactivity)

Living in the deepest part of the Cosmos were some Supreme Beings. Feeling bored, one of these beings took up a hobby.

“I will become a collector,” said the Supreme Being. “I will collect everything that goes to make up the Universe. All the fundamental units that combine to construct every substance in existence. I will call these fundamental units –elements. Such a vast and impressive collection will take aeons to put together.”

And so it sifted through all the matter in the Universe and a short time later, it looked down upon its collection.

“Just ninety two elements! That’s all,” exclaimed the Supreme Being. “Just ninety two!”

But it was inescapable; just ninety-two elements made all the matter in the Universe. Baffled by its discovery, the Supreme Being looked closer. The first element in the collection was hydrogen. The Supreme Being looked deep into the atom of hydrogen and saw at the centre a positively charged proton and circling around it, a negatively charged electron. (Oddly, when it looked at how fast the electron was going, it couldn’t see its location and when it stared hard enough to see where the electron was, it couldn’t see how fast it was travelling.)

It shook the confusion out its Supreme mind and examined the nucleus of the second element in the collection – helium. There were two protons in this nucleus and circling around it were two electrons. Then it examined the third element, lithium, and lo, there were 3 protons and 3 electrons.

“Mmmm,” thought the Supreme Being. “Perhaps there’s a pattern emerging here.”

It then looked at the 92nd element in the collection–uranium – and, there were ninety-two protons and ninety-two electrons. Now bored with the stuff of the Universe, the Supreme Being gave away its collection to a friend and went travelling through a black hole (which took considerably longer than collecting all the elements in the Universe).

One day the new owner of the elements was peering into a hydrogen atom and saw something a little strange. Its friend had said the hydrogen atom comprised one positively charged proton and one negatively charged electron. But there in the nucleus of one of the hydrogen atoms there was something new; something without a charge, a neutron. The Supreme Being at once realised that within any one element there were different varieties, depending upon the number of protons and neutrons in the nucleus. So the Supreme Being sifted through all the hydrogen atoms and divided them into three piles. The first pile had one proton, the next pile had one proton and one neutron and the third pile had one proton and two neutrons. The nuclei of all hydrogen atoms contained one proton but there were three varieties, depending upon the number of neutrons in the nucleus. Those with one proton and no neutrons were by far the biggest pile and so the Supreme Being declared these were hydrogen atoms. Those with one proton and one neutron it named deuterium and those with one proton and two neutrons it named tritium. Rather than call them varieties, the Supreme Being called them isotopes.

No sooner had the Supreme Being discovered isotopes when a postcard arrived from his friend travelling through a black hole. It appeared time was standing still for his friend because the postcard was very long indeed. At last however, our Supreme Being finished reading it and returned to its collection. “Thief,” came a cry which was odd because Supreme Beings are perfect and there were no thieves at that time. “My tritium atoms have been stolen.”

Other Supreme Beings gathered around to see what the fuss was about. “Look,” said one bystander, “is that not them there,” mystically pointing.

“No,” said the owner of the elements, “those are not tritium atoms, those are helium…” The Supreme Being realised that the tritium atoms had not been stolen, they had changed into helium-3 (two protons and one neutron). With eternity available, the Supreme Being sat and observed its collection of tritium atoms. Now and again, a neutron flickered and vanished and in its place one proton, one electron and one anti-neutrino came into being. The tritium isotope that once had one proton and two neutrons, now had two protons and one neutron–it had become helium. As helium formed, an electron and an anti-neutrino sped out of the atom and vanished into the vacuum of space. The electron collided with an interstellar cloud and ionised some gas. The anti-neutrino arrogantly ignored everything around it and passed through clouds and planets alike as if they didn’t exist.

“Well,” thought the Supreme Being. “If anti-neutrinos are so ignorant, then I will ignore them and focus my interest on the electrons.” (Thus proving that even Supreme Beings can make mistakes as anti-neutrinos, and neutrinos, are very interesting to those who study them.) The Supreme Being then declared that the electrons speeding out of the tritium atom would henceforth be known as β-radiation – it had discovered radioactivity.

An advantage of being a Supreme Being is that time means nothing. Be it small amounts of time, a mere flicker of a fly’s wing, or immensely long periods of time where Universes wax and wane. And so our Supreme Being looked through its collection and realised that all the elements were subdivided into isotopes; and the radioisotopes were changing into other isotopes, some in an instant and some over aeons. A mystical, magical dance, the stuff of the Universe intertwining, changing, reacting, swirling, never ending! The Supreme Being could see little minute specks of matter flash out of existence only to become energy that radiated away from the disintegrating atom. The Supreme Being looked down on its collection and said, “wow”!

Uranium turned into thorium, then protactinium through radium and polonium and ending up as lead. From uranium to thorium the journey was long and slow and from polonium to lead it was but a blink of the Supreme Being’s eye (if it had eyes).

“How,” thought the Supreme Being, “can I distinguish between those isotopes that vanish quickly and those that seem to hang around for ever?”

“There are one million atoms in my tritium collection,” it thought. Then it started a cosmic stopwatch and waited until half of those tritium atoms had transmuted into helium; the stopwatch read 12.35 years. The Supreme Being kept looking at the pile of 500,000 tritium atoms that remained and when these had become half that number (250,000) another 12.35 years had passed.

“This,” thought the Supreme Being, “gives me a measure of the rate of atomic decay. Every 12.35 years my pile of tritium atoms reduces by half. Therefore, I will call 12.35 years the half-life of tritium.” (The Supreme Being then worked out all the mathematical equations for exponential atomic decay but it is not in the nature of mythical stories to convey such detail and so we will move on).

The Supreme being then catalogued all the isotopes in its collection. It counted 253 isotopes that were stable and the rest were radioactive. Of the radioisotopes, many had half-lives so short it was difficult to measure them (even Supreme Beings have some limitations). A total of 289 isotopes had half-lives of between one day and 10,000 years and 84 had half-lives greater than 10,000 years. Tellurium-128 had a half-life of 2,200,000,000,000,000,000,000,000 years. In fact this was so long that several Universes began and ended before The Supreme Being could figure out a value for the half-life of tellurium-128.

Just then, the Supreme Being’s friend came back from its holiday inside a black hole. Seeing that its collection had turned from a boring pile of atoms into a psychedelic, intertwining, choreography of interchanging isotopes, the returning Supreme Being demanded the return of its collection. The current owner of the isotope collection thought this a little unjust and refused. A little after this, the Supreme Beings invented war, and the Universe was never the same again. The study of the atom and radioactivity was therefore left to the inhabitants of a little blue-green planet called Earth. Ironically, the inhabitants of Earth often fought wars over which Supreme Being one side or another thought the most supreme – but that is a different story.

Antibiotic from breast milk – really?

The headlines read:

New drug to wipe out superbugs – antibiotic ‘bullet’ created from breast milk (The Times)

Breast milk could wipe out hospital superbugs and even incurable diseases (Express)

Breast milk protein could be used in fight against antibiotic resistance (Guardian)

Breast milk protein could destroy antibiotic resistant superbugs (Independent)

Drug resistant bugs destroyed by new antibiotic from breast milk discovered by British scientists (Mail)

The stories themselves contained little information on what this new antibiotic was. The original story seems to have come from an interview with the Times but all the newspaper reports were remarkably similar containing all the same quotes and statistics. In fact they were all so similar that if I had seen these in student essays I would have very good grounds for a case of plagiarism. This is makes it a pretty good bet that it all came from a press release that was copied from one news outlet to another – a common practice it seems.

The report on the Express website included a video clip of Dr Freya Harrison, of the “School of Life Science” who appeared to be proclaiming her surprise about how powerful the medication was. When I checked however, Dr Harrison had nothing to do with the so called breast milk antibiotic. She is in fact a respected academic at the University of Nottingham’s Ancient Biotics Project. The clip was about the antimicrobial properties of some ancient remedy, undefined in the video, and completely unrelated to the story.

This story had done the rounds as I also found it on websites such as The Economic Times Pharmaceuticals section, where incidentally they had linked the story in error to the Royal Society instead of the Royal Society of Chemistry.

The gist of the story seems to be that a breast-milk protein called lactoferrin was found to “kill bacteria and viruses on contact.” Most reports said it was developed jointly between the National Physical Laboratory and University College London. Since the antimicrobial action of lactoferrin has been known for a long time, I wondered why this was considered a breakthrough and so I dug a little deeper.

The original paper that caused all this excitement was published in Chemical Science and can be found here. It was a little tricky to track down from the limited information given in the press, as any search using “breast milk” came up blank (or to websites I’m not going to mention!). The paper is very technical and I am sure journalists without a great deal of specialisation could not interpret it. I am a pharmacologist and I admit I had to spend some time on the various technical terms before I could grasp the meaning. This is normal with a scientific publication as it’s meant for the science community not the lay public.

The antimicrobial is in fact a very innovative piece of protein engineering exploiting a naturally occurring protein called lactoferrin. Although, as I said above, lactoferrin is indeed found in breast milk, it is also found in saliva but I guess a headline proclaiming a new wonder drug coming from spit doesn’t have the same appeal to the media. Essentially the science behind this has nothing to do with breast milk at all other than the protein can be found there. I wonder, when penicillin was first discovered, if the headline was “pneumonia cured by mouldy bread?”

Lactoferrin was engineered so it formed a self assembling virus-like structure they called plastic peptide capsules. The researchers chose lactoferrin because it has antimicrobial properties in that it binds to the surface of bacteria and it is non-haemolytic (does not burst red blood cells). Once bound, it punches a hole into the bacterial cell wall. This will kill the bacteria but the virus-like structure could also deliver a siRNA payload. siRNA (Small Interfering RNA) is a nucleic acid that interferes with the expression of certain genes. It was a serendipitous discovered by Richard Jorgensen when he was investigating stippling on the petals of petunias. Jorgensen won the Nobel Prize in 2006.

The intrinsic therapeutic properties of siRNA are well recognised but the nature of these molecules makes them very difficult to deliver to their biological target. This new structurally engineered protein may be one approach for siRNA delivery but the researchers were careful to point out that this was a conceptual design.

The real story was therefore far more interesting and exciting than the newspapers actually reported. This is real cutting edge science where molecules are constructed for specific functions. Like virtually all of science, it wasn’t a breakthrough rather than a step in the painstaking process of research. But there was not a whisper of this in any of the media reports I could find. It was, I guess, just easier for the journalist to take the original story, jiggle a few words around and go to press without worrying if it was accurate or not.

Does it matter that the press didn’t report what was a highly technical piece of science properly? Well, yes, it is very important. Surveys over many years have shown that the public’s main source of information on science comes from the general media (eg Ipos MORI Survey, commissioned by the Government Department of Business, Innovation and Skills in 2014). If the press cannot be bothered to do their job properly then how can the public’s understanding of science be anything than corrupted. This was exemplified by a comment (on the Mail website admittedly) that said, “there are so many amazing natural cures for a huge variety of ailments, but big pharma will mock and deride them on a massive scale so that anyone who praises natural remedies is deemed to be a nut bag….” Ironically, the truth behind the story was not about a natural cure, but a highly engineered protein that may one day be developed by the Pharmaceutical Industry to treat serious disease.

Pseudoscience versus science – is there an answer?

I first became aware of pseudoscientific nonsense when I was a student back in the 1970s. I remember many of my fellow students buying little plastic pyramids in the belief it gave them more ‘energy’ or made them smarter – particularly around exam time. A good friend of mine was an acupuncturist and was prone to pointing out meridians on the diagrams in my anatomy textbooks, almost as if the authors had forgotten to include them. I admit I was tempted by some of this but I never really bought into any of it. Perhaps my memory of events has edited itself since that time but I recall that when I challenged the dubious beliefs of some of those around me, I was answered with “science doesn’t know everything” and “there’s more to the world than science you know.” There seemed to be a dividing line between the natural and the supernatural and you either believed in the latter or you didn’t.

Nowadays I find things rather different. Many pseudosciences are trying to hijack genuine science and I don’t just mean those shampoo advertisements that plagiarise technical-sounding language. Some pseudoscientists are proclaiming themselves as the true scientists whilst portraying those who disagree with them as blinkered and ignorant. My early experiences when science was just dismissed as ‘not knowing everything’ was a more honest approach than the current trend that tries to turn truth on its head.

Science has given us much in the modern world, including real effective medicines and vaccines and perhaps it’s this success that the pseudoscientists wish to latch onto. The problem is however, that the way much of the gibberish is sold in the false name of science exposes its own perversion; for saying something is scientific is not synonymous with saying it is correct. Science is not so much about facts but about a method of getting to the facts. It starts with a hypothesis tested to destruction with the intent of proving it wrong. Only if it stands up to this deep scrutiny does it become promoted to a theory, but even then it is open to modification and disproof. (I have a YouTube video that attempts to explain the scientific method in 15-minutes).

Science is the toughest of masters. It is indifferent to egos or careers and can shoot down someone’s pet theory without a second glance (I have personal experience and so I know). Those that just want to evoke the name of science to support their own point of view find this very hard to grasp. And then criticism of their fantasy often triggers personal derision in response.

Most pseudoscientists have had no scientific training and are like someone proclaiming themselves a world-class concert pianist without ever having had a piano lesson. They get onto the stage and then just bang away at the keys. They might attain a following of those who enjoy such avant garde music but then they claim their rendition of Mozart’s piano sonata is far superior to that played by professional pianists who have spent years perfecting their art. This does not mean that science is the exclusive property of scientists – far from it. It means that if you don’t understand something, you can’t just make something up to fill the gap.

Our understanding of nature is evolving and changing all the time and it’s likely that the physics of 20 years time will say different things to what it does today. The discovery of dark matter and dark energy, for example, are likely to lead to a rewriting of the standard model of physics. The rigour and robustness of this science however, versus that of pseudoscientific research (if that’s not an oxymoron) are light years apart. In the meantime there will be those that will blur the edge between science and pseudoscience to sow the seeds of confusion. I find this worrying, not because I feel that science itself is threatened but because those still deciding which path to take can be seriously misled.

Birth of the Salk Vaccine

The 12th April, 2015 is the 60th anniversary of one of the pivotal points in medical history, when results of the clinical trial of Salk’s polio vaccine showed it was safe and effective in 80-90% of children. Today we have witnessed a 99% worldwide reduction in polio and organisations such as the Gates Foundation are striving to rid the globe of that last 1%, although it still persists in Nigeria, Pakistan and Afghanistan.

Before Jonas Salk, the prevailing wisdom was that vaccines had to be made from the living virus. An early live polio vaccine however, led to the deaths of children, which unsurprisingly put the breaks on further development for several years. Salk worked on the idea that a dead virus (inactivated with formaldehyde in the case of polio) would still elicit an immunological response and provide the vaccinated individual with the army of antibodies needed to fight the disease. Leading virologists of the time, such as Albert Sabin, disagreed that a dead virus would be effective and Salk found himself battling the scientific orthodoxy of the day. A small scale safety trial was first carried out with Salk’s vaccine in children that had naturally recovered from polio. The success of this trial then led the way to larger-scale trials. The final clinical trial included a placebo group, which Salk was unhappy about on ethical grounds. Salk himself was kept out of any involvement with this final trial to ensure an impartial assessment. In fact, the design of these studies laid the foundations of many clinical trials to come.

Sixty years ago today Salk’s approach was vindicated, and he became an overnight celebrity. He refused to patent the vaccine, saying it was science’s gift to mankind. Some years later his main opponent, Albert Sabin produced his effective vaccine but also declined to profit from through a patent.

Before Salk’s vaccine, polio caused untold mystery and death. In the 1930-40s the summer months heralded the start of the polio season. Parents of the poor and wealthy alike lived in terror of the disease that seemed to strike at random. In 1952 there were 58,000 cases of polio in the United States which led to 3145 deaths. The UK of the 1950s, there were an average of 8,000 cases of polio per year. The Salk vaccine became available in Britain in 1956 which was followed by the Sabin vaccine in 1962. The polio epidemic of the 1940s-50s rapidly fell away and thankfully has not returned.

The overriding success of vaccination is one of the great medical victories against infectious disease. To deny their huge therapeutic impact is to deny history and a vast mountain of evidence, but this does not stop a minority anti-vaccine lobby from very vocal objection. Some diseases of the past are now returning because of doubt sown in the minds of parents by the likes of the now discredited Andrew Wakefield

How is it possible to turn our backs on the history of infectious disease that is still within living memory? The story of Salk is a triumph of the scientific method and we should remember this anniversary as a milestone of rationality, else we turn back the clock and return to an age of superstitious pseudoscience to herald the return of the plagues.

Mass poisoning and emergence of life

A paper recently appeared in Nature Geoscience that may have found the oldest case of mass murder by poisoning. Think of ancient cases of poisoning and your mind might go back as far as the ancient Greeks and their inclination towards hemlock (the Greek philosopher, Socrates died of hemlock poisoning in 399 BCE). But the ancient Greeks were just yesterday compared to the latest ideas around mass extinctions some 3- billion years ago.

The early cyanobacteria developed the neat trick of combining water and carbon dioxide to make sugars and the other molecules of life, such as amino acids and proteins. To do this, the cyanobacteria needed energy and they got that from sunlight. This neat trick is still around to this day and we call it photosynthesis. As the cyanobacteria started to photosynthesise, so they became the antisocial life-form from hell, for they produced a deadly poison – oxygen.

To us oxygen is essential for life but the early earth was devoid of atmospheric oxygen. Three billion years ago the atmosphere may have contained one ten thousandth of a percent oxygen, compared with today’s value of close to 21%. Oxygen however, is very reactive and strips electrons from organic molecules. Life 3-billion years ago was anaerobic and the buildup of oxygen in the atmosphere represented a real threat. Existence of animal life today is only possible because of some intricate biochemistry that protects from oxygen toxicity.

The 3-billion year old mass poisoning referred to here however, was not caused by oxygen – in fact just the opposite. An ability to utilise oxygen to generate energy from food is a much more efficient processes than anaerobic metabolism. Evolutionary pressure favoured those early organisms that evolved ways of harnessing oxygen and by two an a half billion years ago, oxygen-utilising life was the norm. Timescales raises a question however, and that is why did is take 500 million years for oxygen-based life to become dominant. The answer may well be iron toxicity.

The theory is that volcanism boiled up large amounts of iron from the inner core of the earth, which ended up in the archaean oceans. Iron exists in different oxidation states of which two dominate, know as Fe2+ and Fe3+. Since electrons are negatively charged, as iron atoms lose electrons, so they gain a positive charge. If the iron atoms loses 2 electrons, it gets two positive charges (Fe2+) and if it loses 3 electrons then it gets three positive charges (Fe3+). One good way of losing an electron is by reacting with oxygen. As iron poured into the the archaean oceans so it reacted with the emerging oxygen preventing the buildup of the gas in the atmosphere. Presence of Fe2+ was also toxic to much of the emerging life and so evolution of complex life was inhibited by half a billion years. When the amounts of oxygen eventually overwhelmed the available iron, so atmospheric oxygen rose, in the great oxidation event that took place around 2.5 billions years.

Interestingly without volcanic iron, life on earth (and by inference ourselves) would be half a billion years older. By now we may have evolved beyond being human, we may have colonised the stars or we may have had time to become extinct – who knows?