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Research, Science

Why does the Earth’s magnetic field reverse?

GEOPHYSICS

Intro: One of the properties of our planet that we have struggled to explain is the fact that its magnetic field occasionally reverses. If this happened today, it would mean that our compasses would point to the south, rather than to the north.

A reversal in the magnetic field is probably not something we need to get overly worried about because the last full one occurred 780,000 years ago, while a partial reversal, known as a geomagnetic excursion, last happened 41,000 years ago – when the poles reversed for a few hundred years before flipping back again. The generally accepted theory of how the Earth’s magnetic field is generated states that heat from the solid inner core of the planet causes chaotic and swirling convection currents in the liquid outer core, and, as it is predominantly composed of magnetised iron, this rotational movement works like a giant dynamo, inducing a moving electric current, together with its accompanying magnetic field. The action of this geodynamo, as it is known, is thought to lead to the polarity of the planet and to maintain the magnetosphere, the region of space around the Earth to which the magnetic field extends.

The possibility of the magnetic field reversing was first proposed in 1906 by the French geologist Bernard Brunhes, after he had studied iron minerals in volcanic rocks from Auvergne, the region of central France well-known for its numerous extinct volcanoes. This was based on an anomaly he observed, in which some crystals of magnetic iron minerals in the volcanic rocks are orientated either to the north or south. Shortly afterwards, the Japanese geophysicist Motonori Matuyama carried out a systematic study of volcanic basalt rocks in different locations in Japan and China, which demonstrated that rocks in the same geological layers – ones that had been laid down at the same time – showed the same polarity, described as normal where iron minerals are oriented to the north, and reversed in those pointing south.

The volcanic landscape of the Massif Central in the Auvergne, France.

Matuyama’s work provided clear evidence to support the theory that the poles had reversed in the past, but it did not receive any great attention until the 1950s, when radiometric methods of dating rocks based on the decay of radioactive isotopes were developed, which allowed a chronology to be worked out. The pioneers of this field were later recognised, with their names being assigned to the periods, known as chrons, of normal or reversed polarity. We are currently in the Brunhes Normal Chron, which began 780,000 years ago, and this was preceded by the Matuyama Reversed Chron, beginning 2.59 million years ago, while the period during which the flip took place is called the Brunhes- Matuyama Transition. It used to be thought that this flip occurred over the course of thousands of years, but recent research, published in 2014, suggests that it could have been made quicker, perhaps taking as little as 100 years.

The Flipping Field

We don’t know what causes a reversal in polarity and may well have to wait until it happens again before we have the opportunity to study the phenomenon in enough detail to find out. We currently lack a clear enough understanding of what is happening in the outer core and mantle to generate the magnetic field in the first place, let alone know why it flips. Past reversals have occurred over an apparently random time frame, so it is impossible to predict when the next one will be. A gradual weakening of the magnetic field recorded over the course of the last century has led to some speculation that we are entering a transitional period, but, as we don’t know anything about the processes leading up to reversals, there is no way of knowing if this is really the case. A reversal may be beginning right at this moment, or it may not happen for hundreds of thousands of years.

 

One way of investigating reversals in the Earth’s polarity is to construct computer models of the way in which the Earth’s magnetic field is generated by the dynamo in the inner core, and then run simulations to see what happens. This involves attempting to recreate the interaction between the heat generated in the inner core and the convection currents thought to be the source of the magnetic field in the outer core, which, as we don’t fully understand what is going on in either region, is extremely difficult. One simulation developed by Gary Glatzmaier and Paul Roberts at University College, Los Angeles, in the 1990s, uses a complex set of equations, involving thermodynamics and fluid motion, to describe the physical properties of the geodynamo. It was found to provide an accurate model for the generation of known variations in the magnetic field, and, when run to simulate the changes occurring in polarity over hundreds of thousands of years, showed the process of reversal occurring on a number of occasions. The timing of the reversals was random, and apparently caused by the development of a particular set of circumstances, in which the thermodynamics and fluid motion evolved with the generation of the magnetic field in such a way as to weaken the strength of the poles. If the strength of the poles dropped below a certain point, this caused a reversal.

The Impact of Reversals

If computer-generated models accurately simulate what is happening in the outer core, and reversals are indeed caused by a weakening in the magnetic field, then this has implications for the ability of the magnetosphere to deflect potentially harmful high-energy particles found in cosmic radiation. If the magnetic field were to disappear completely, the planet could also be exposed to solar wind. This is thought by some scientists to have occurred on Mars, which does not have a magnetic field, and thus any atmosphere that may have existed would have effectively blown away. Needless to say, this would be disastrous for our planet, but as there have been numerous reversals in the past and the Earth still has an atmosphere, it is reasonably safe to assume that this scenario is not very likely to happen here.

 

Studies of transitional periods that lead to reversals and their impact on life on Earth have actually found nothing to suggest any harmful effects. There is, for instance, no correlation between the timing of reversals and extinction events or periods of increased seismic and volcanic activity. So it would appear that, beyond the disruption it would cause to our navigational systems, and the possibility of interference with some communications, we don’t have a great deal to worry about. There could be an impact on animals that make use of the magnetic field to navigate, though it would appear that reversals usually happen over the course of long enough periods to allow them to adapt. In the unlikely event of a flip suddenly happening tomorrow, aircraft may have to be grounded while we work out how to navigate, our phone services could be interrupted for a while, and homing pigeons might get rather confused.

Alternative Theories

In recent years, seismic images of the Earth’s inner core have been interpreted as showing it to be composed of slightly differing eastern and western hemispheres. One theory, known as translational instability, suggests that this difference is due to the growth of the core, caused by its cooling, being lopsided – with more iron crystallising out on the surface of the western side than on the eastern one.

In research published in 2012, Peter Olson and Renaud Deguen of Johns Hopkins University in Baltimore, Ohio, set-out to test this theory, by modelling what would happen to the magnetic field if the inner core were lopsided. They found that the axis of the magnetic field in the model shifted to the side that was growing, which led them to speculate that this change in the axis in the inner core may cause irregular convection patterns in the outer core, which could be responsible for reversals in the magnetic field. They also thought that the position of the axis in the inner core could be the reason why magnetic north is not the same true north – the Magnetic North Pole currently being off the coast of Canada, about 480 km (300 miles) from the Geographic North Pole. If this is correct, then tracing the movement of the Magnetic North Pole over time would give an indication of the way in which the inner core was growing, and perhaps would even show if a reversal in the magnetic field were likely to occur.

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Health, Medical, Research, Science

Brain health linked to how young or old you feel

NEUROSCIENCE STUDY

Besides improving your physical and mental health, feeling younger can also slow down the rate of brain ageing, finds a study.

THE young at heart often insist you are only as old as you feel.

A newly released study has proved they are right, finding that those who feel younger than they are show fewer signs of brain ageing.

Neuroscientists who gave a group of people aged 59 to 84 MRI scans found that those who said they felt younger had more grey matter in their brains and did better in memory tests.

The researchers suggested that those who feel their age or older have picked up on small cognitive changes in their brain, such as mild memory loss. The study, carried out by the University of Seoul in South Korea, is the first to link how old people feel with the physical signs of brain ageing.

Co-author Dr Jeanyung Chey said: “We found people who feel younger have the structural characteristics of a younger brain.

“Importantly, this difference remains robust even when other possible factors – including personality, subjective health, depressive symptoms or cognitive functions – are accounted for. If somebody feels older than their age, it could be a sign for them to evaluate their lifestyle, habits and activities that could contribute to brain ageing and take measures to better care for their brain health.”

The researchers asked 68 healthy people whether they felt older or younger than they were, or whether they felt their age. When their brains were scanned, those who felt younger had more grey matter in key regions such as the hippocampus which is linked to memory.

The scans showed their brains had actually aged less than those of people who felt older, as grey matter tends to decline with age.

The youthful-feeling group also did better in memory tests, including tasks such as recalling details from a story 15 to 30 minutes after hearing it. The researchers suggested that those who feel older may be able to sense the ageing process in their brain as their loss of grey matter may make cognitive tasks more challenging.

Another possibility is that those who feel younger are more likely to lead a more physically and mentally active life, which could cause improvements in brain health. Previous studies have suggested that asking people how old they feel can predict if they will develop dementia, become frail or be taken to hospital. Those who feel older than their age are also more likely to be overweight and suffer illnesses associated with being obese.

Dr Chey, whose study was first published in the journal Frontiers in Aging Neuroscience, said: “Why do some people feel younger or older than their real age?

“Some possibilities include depressive states, personality differences or physical health.

“However, no one had investigated brain ageing processes as a possible reason for differences in subjective age.”

The results suggest that feeling older than one’s age may reflect relatively faster ageing brain structures. Those who feel younger have better-preserved and healthier brain structures.

Some of the biggest changes in grey matter based on age perception were found in the inferior pre-frontal cortex, which helps in suppressing irrelevant information. Loss in this region could cause age-related problems in tasks requiring focus and concentration.

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Health, Medical, Research, Science, Society

What can we do about antibiotic resistance?

ANTIBIOTICS

Intro: In 2014, the World Health Organisation (WHO) stated that antibiotic resistance was “happening right now in every region of the world” – leaving us at risk of entering a “post-antibiotic era”, where common infections could once again become fatal.

The WHO’s first global report on antibiotic resistance may sound alarmist, but it reflects the crucial role antibiotics have played in treating microbial diseases and infections since first becoming available in the 1930s.

Antibiotics were discovered in 1928 by the Scottish bacteriologist Alexander Fleming while he was working at the St Mary’s Hospital Medical School in London. During the First World War he had served as a medic in military hospitals behind the Western Front, where he witnessed the death of many soldiers from wounds that had become septic as a consequence of bacterial infections. After the war, Fleming directed his research efforts towards finding better ways of dealing with such infections and, according to his later account, discovered penicillin through chance and luck. A fungal mould of the genus Penicillium had infected a Petri dish containing a bacterial culture, after the spores had apparently blown into Fleming’s laboratory through a window that had accidentally been left open. As he was about to throw the Petri dish away, Fleming noticed that the bacteria around the mould had been killed, leading him to isolate the active substance produced by the mould, which he named penicillin.

A Medical Revolution

It took ten years for any serious work to start on developing penicillin into a usable antibiotic and, in the meantime, the German pharmaceutical company Bayer developed the sulphonamide antibacterial drugs, sold under the name of Prontosil. The beginning of the Second World War led to renewed interest in penicillin, and a team at Oxford University – led by Howard Florey and including the Jewish, German-born Ernst Chain, who had fled Germany in 1933 to escape persecution – developed a method of producing penicillin for medicinal use. For this work they, together with Fleming, were later awarded the Nobel Prize for medicine.

Making enough penicillin for armies during the Second World War proved difficult until deep fermentation was developed in America, coming just in time to provide sufficient supplies for the armed forces during the invasion of Normandy in June 1944. After the war, further research improved penicillin, and other antibiotics were developed, leading to a medical revolution that, coupled with the widespread use of vaccines, has dramatically reduced the impact of fatal or debilitating diseases and infections.

Growing Resistance

Almost as soon as he began to work on penicillin, Alexander Fleming recognised the potential for bacteria to develop resistance, because of the capacity such microbes have to replicate very rapidly, providing the opportunity for evolution to occur. Should a mutation arise which confers resistance, it can spread quickly – facilitated by the further use of antibiotics, because these would then wipe out any non-resistant bacteria that would otherwise compete with the resistant strain. Despite repeated warnings by Fleming and many others not to misuse antibiotics, it quickly became common practice for doctors to prescribe them for a much wider range of illnesses than they should have, often simply because patients demanded them.

Today, antibiotics are still being given to patients who have colds or flu – viral infections against which such treatments are ineffective – and are also widely used in veterinary medicine as a preventative measure in livestock farming rather than as a treatment for a specific disease. In some countries, antibiotics are also used as growth promoters in livestock, it having been found that animals treated in this way often perform better. About two-thirds of all antibiotics are now used on farms, and while these are different from the ones used to treat people, such use can nevertheless result in a build-up of resistance, which has the potential through genetic mutation to transfer to medicinal human antibiotics.

Resistance will build up in bacteria even where antibiotics are used responsibly, but the more they are used, the quicker this will happen, so it is vitally important that they are not overprescribed or misused in livestock farming. Unfortunately, this advice has not always been followed, leading to a number of infectious diseases becoming increasingly difficult to treat. Some of the best-known examples are those particularly associated with hospitals, known by most people as “superbugs”, such as MRSA (methicillin-resistant Staphylococcus aureus). These bacteria are not necessarily any more virulent than strains that remain sensitive to antibiotics – the problem being that they are much more difficult to treat, particularly those which have become what is known as multidrug-resistance. Stricter regimes of hygiene in hospitals have been found to minimise the spread of MRSA, but it nevertheless represents a serious and ongoing problem for healthcare.

Multidrug-resistant Mycobacterium tuberculosis is another microbe becoming more common worldwide. As its name suggests, this bacterium is responsible for tuberculosis, a potentially fatal infectious disease of the respiratory system, which was thought to be under control through the use of antibiotics until the 1980s, when resistant strains began to emerge. Today, more than 100,000 people are thought to die every year as a consequence of this resistance – many of whom live on the African continent, where treatment may not be available and where, in some cases, those infected already have an immune system weakened by HIV.

Developing Solutions

One potential solution to antibiotic resistance would be the regular introduction of new classes of antibiotics to which pathogens have no resistance, but so far this has not happened. Big pharmaceutical companies, responsible for the design and introduction of most new drugs, have been reluctant to invest in developing new antibiotics because it is difficult and expensive, and antibiotics are not very lucrative compared to other classes of drugs. Patients usually only need antibiotics for about a week, and new ones would only remain effective for as long as it took for resistance to build up, which can take just a few years. Drugs for conditions such as heart disease, for example, are often used for long-term treatments so, once pharmaceutical companies have made the initial investment involved in development and clinical trials, they can expect to sell successful drugs for a much longer period.

In its 2014 report, the WHO identified serious gaps in available information on the types of antibiotic resistance occurring globally, which, together with a lack of coordination between countries, was impeding possible responses to what has become a serious problem. As well as stating that increased information gathering, and sharing is needed, the report recommended greater government investment in research, and the responsible use of antibiotics in medicine and agriculture. Everybody has a part to play, though, from doctors not overprescribing antibiotics to patients using them exactly as prescribed.

Alternative Theories

In January 2015, researchers at Northeastern University in Boston, Massachusetts, reported that they had discovered a new antibiotic named teixobactin, which they had isolated from the soil bacterium Eleftheria terrae through a new culturing method. It was the first new class of antibiotic to be found for almost 30 years, and in tests proved effective against a range of bacteria, including MRSA and Mycobacterium tuberculosis, neither of which appeared to develop resistance to it. Teixobactin works by inhibiting the production of those fats that form a constituent part of cell walls and preventing bacteria from growing, while most other antibiotics target proteins in the cell wall or inside the cell to kill fully grown bacteria. The research team thought that E. terrae might have developed this function in response to naturally occurring resistance.

If they are correct, resistance to teixobactin is less likely to develop in the first place and, even if it does, will take much longer to build up than resistance against existing antibiotics. Clinical trials should take about five years and, if it passes, the research team predicts that teixobactin could remain effective for over 30 years. Even if teixobactin fails these trials, this new method of culturing soil bacteria in the laboratory can be used to investigate the potential of many other species of bacteria to produce antibiotics. This on its own could lead to a whole new era in the fight against antibiotic resistance.

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