2014年6月29日 星期日

Five insights challenging science's unshakable 'truths'

Five insights challenging science's unshakable 'truths'

If you thought dying of loneliness was just an old wives' tale, or that genetic inheritance is fixed – think again. Michael Brooks on science's most unexpected findings
Methyl groups, which affect our genes, often come from what we eat.
Methyl groups, which affect our genes, often come from what we eat. Photograph: Science Photo Library

1 | Lifestyle can change genes

We have come to think that if something is "in our genes", it is our inevitable destiny. However, this is a gross oversimplification. We have each inherited a particular set of genes, but the outcome of that inheritance is not fixed. Our environment, diet and circumstance flood our bodies with molecules that switch the genes on or off. The result can make a huge difference to our destiny – and that of our descendants.
One example of these "epigenetic" changes occurs when a bundle of carbon and hydrogen atoms known as a methyl group attaches itself to the DNA and changes the way its instructions are carried out. The degree of the effect depends on the exact shapes into which the DNA in cells is coiled; sometimes certain genes become more or less exposed to external influences. But it can have major effects: the effect of methyl groups on DNA can make the difference between a foetus being healthy or stillborn.
Methyl groups often come from what we eat. Lack of food seems to have an epigenetic effect, too. A study of Dutch women starved by the Nazis during the second world war – the British actress Audrey Hepburn was among them – has found elevated levels of schizophrenia, breast cancer and heart disease. The data suggest that the alterations to which genes are turned on or off survive at least two generations: the one that suffered in the womb during the famine, and their children.
They may go much further. A 2011 study published by researchers at the Salk Institute in La Jolla, California, demonstrated epigenetic mutationsthat lasted for at least 30 generations in plants. So far, we haven't proved such long-term changes in humans but there are hints that epigenetics cascades through the generations.
A 2001 study traced the long-term effects of nutrition – and malnutrition. Controlling for socioeconomic factors, a boy approaching puberty who overate at the beginning of the last century generally reduced his grandson's life expectancy by a whopping 32 years. Other studies show that if boys start smoking before the age of 11 their sons will be significantly more overweight by age nine than their peers with fathers who only took up smoking later. The only way this can happen is if the act of smoking tobacco triggers some epigenetic change in the way DNA is activated in their sperm.
Standard biological thinking says that the body strips away molecules such as a methyl group from sperm and eggs so that they are "reset" to their default state. However, a study published by Cambridge researchers last year showed that approximately 1% of the changes get through the erasure process unscathed. What you eat, what your mother ate, the age when your grandfather started smoking, the amount of pollution in your neighbourhood – these factors have all been linked to epigenetic changes that get passed down through the generations. Armed with this new insight, we can take far more control of our health – and the health of future generations.

2 | The mind can affect the body

positive and negative moodPositive thinking: the state of our mind affects our physical health. Photograph: Alamy
The US National Oceanographic and Atmospheric Administration has a piece of advice for anyone trying to survive immersion in freezing cold water: "Keep a positive attitude. Will to live makes a difference." Does it really? It seems so.
We know that simple mind tricks can suppress the immune system in animals. First, you teach rats to associate saccharine with a stomach upset by spiking sweet drinks with a drug called cyclophosphamide. Then you just give them saccharine. They will be significantly more susceptible to pathogens than animals given saccharine but no conditioning.
Humans are not exempt from mind-immune system connections. Research carried out on 4,000 people over a 12-year period showed that a man whose wife has just died had a 25% higher chance of dying in those 12 years. The bereaved reported heart and circulatory problems twice as often as people in the control group.
In 2010 a study conducted in the US enumerated the dangers of loneliness. If you have "adequate" social connections, you are 50% more likely to live to the end of a specified period than those who are lonely. In other words, the effect of having good friends is roughly similar to giving up smoking or making a significant cut to your intake of alcohol. A 2012 study, which followed 2,000 US citizens aged 50 and above, found that being chronically lonely was associated with being almost twice as likely to die over the period of the study. Another 2012 study found that elderly people who simply want to live longer do indeed have a better life expectancy regardless of their physical health at the time their desire is expressed.
What used to be dismissed by science as superstition or old wives' tales is now coming to the fore. The state of our minds has a palpable effect on our bodies, meaning that we are finally learning how to protect ourselves better from the worst ravages of illness.
Such knowledge is improving our state of mind too. In 2011 Hasse Karlsson, professor of psychiatry at the University of Helsinki, looked at 20 studies of brain changes induced by psychotherapy and concluded that we are moving towards a situation where we know so much about what psychotherapy does – how our subjective experience can be manipulated to change the physical structures of the brain – that specific types of psychotherapy can be used to target particular brain circuits. As Nobel laureate Eric Kandel has put it: "Psychotherapy is a biological treatment, a brain therapy."
Sigmund Freud started this field in 1895. However, his "Project for a Scientific Psychology" was a miserable failure because we knew too little about the brain. Now, though, we have much better tools with which to explore the mind's effect on the body, and Freud's abandoned programme is finally bearing fruit.

3 | Quantum effects exist in biology

Plants use quantum theory to harvest energy from the sun.Plants use quantum theory to harvest energy from the sun. Photograph: Power & Syred/SPL
If you were designing life from scratch, you'd probably want to avoid the vagaries of quantum theory. Quantum particles such as atoms and electrons do strange things. They can be in two different places at once, or be affected by measurements performed on other particles. Surely such things could only be a hindrance to the smooth functioning of life's processes?
That's certainly what the physicist Erwin Schrödinger said in 1944. Life, he decided, had to be built on a scale that would bury all the weird quantum effects. But Schrödinger was wrong. Plants, for instance, use quantum theory to harvest energy from the sun.
Experiments performed on algae (their light-harvesting equipment is a little more accessible to experiments) have shown that they can channel the sun's energy using "superposition", where the energy travels through the organism using many paths at once. This trick effectively searches all possible paths simultaneously, and finds the quickest and thus most energy-efficient route. That means the energy reaches the plant's storage centre before it dissipates.
There are also hints that smell is a quantum sense. Our noses appear to work by sensing the natural vibration frequencies of the bonds between atoms in molecules. Those frequencies determine whether a smell receptor is switched on and sends a signal to the brain. The best explanation for experimental observations involves an electron using a phenomenon known as quantum uncertainty to tunnel through a seemingly impenetrable barrier. Essentially, it borrows energy from the universe in order to leap across an empty space in the smell receptors and trigger the brain's sense of smell. As long as it returns the energy quickly enough, the electron can use as much as it needs. This "quantum tunnelling" phenomenon is also at the heart of modern electronics."
Then there's the navigation trick birds use for migration. Studies of the European robin (and the robin had to wear a cute little eyepatch during this research) suggest that a particular configuration of a molecule in the robin's retina – a configuration that can only be explained by the rules of quantum theory – allows the bird to sense Earth's magnetic field and thus determine the direction in which it should fly.
We don't know what other quantum feats nature performs, but the fact that these things happen in the warm, wet world of biological material suggests that we are missing a trick. At the moment, we can only access the quantum world if we cool atoms and molecules down to near absolute zero and isolate them from all vibrations and other disturbances. If we can work out how nature functions without such precautions, we might be able to harness quantum theory for ourselves, creating highly efficient solar panels, for instance, or super-sensitive navigation tools.

4 | The universe is a computer (and we are the programmers)

A stellar-mass black holeThe study of black holes has led scientists to question the very nature of reality. Photograph: Nasa
At the forefront of knowledge – the place geneticist Jacob Bronowski once referred to as "the edge of uncertainty" – the biggest thinkers are starting to come to terms with an extraordinary idea. The universe, they say, behaves exactly like a computer, processing and generating information. In this scenario, we, by our conscious and unconscious actions, are playing the role of that computer's programmers.
The first person to think of the cosmos as a human-powered computer was science-fiction author Isaac Asimov. In 1956, in The Last Question, he imagined a situation where two people engage in a bet that ends with humanity absorbed into the intelligent processor that we know as the universe. This was the inspiration behind Douglas Adams's depiction of the Earth as a supercomputer in The Hitchhiker's Guide to the Galaxy.
Truth, though, seems to be stranger than fiction. In the past few years, MIT engineer Seth Lloyd has calculated that a single atom can carry 20 binary digits (bits) of information and that two atoms can collide with an outcome that is entirely equivalent to the information processing that goes on within a computer. The concentration of chemicals within a mix can also store bits: cause these chemicals to react together, and they too can process the information like a computer. Viewed from this perspective, the whole universe is busy performing computations.
According to Lloyd's calculations, a kilogram of matter can perform around a million billion billion billion billion billion operations every second. That processing power is applied to about 10 thousand billion billion billion bits of information. Since time began, Lloyd has calculated, the universe has performed around 10 to the power of 122 operations on 10 to the power of 92 binary digits. What are those operations? We see them aschemistry and physics, as the processes of life and the mechanisms of thought.
There are many more implications to this branch of science – it appears, for instance, that what we call reality is actually a projection of information held at the edge of the universe. The conclusion comes from the study of black holes. One of the sacred laws of physics is that information can't be destroyed. That's a problem when you consider the information contained in things that fall into black holes – unless it remains at the event horizon, which is the spherical "point of no return" surrounding a black hole. That means all the information about what's inside the black hole is held at its edge. If that's true for black holes, it's probably true for the universe as a whole. And that means we are effectively the "holographic projection" of the information held on the spherical shell of the universe.
Whatever the truth we eventually settle on, it seems that life does have some meaning. Where scientists used to say we live out a purposeless existence, it turns out that we, by our actions and minds, are programming the universe. Or, as Carl Sagan put it: "We are a way for the universe to know itself."

5 | Human beings are nothing special

Monkey hand taking peanuts from a human hand Humans are not the only animals that use tools or have personality types. Photograph: Tim Gainey/Alamy
We have been taught to think of ourselves as the pinnacle of creation, but that pinnacle is getting rather crowded. In many cases, crows and chimps can use tools – and sometimes abstract reasoning – better than humans. If it's culture that makes you feel superior, visit the Tanzanian Gombe chimps, Canadian killer whale communities or Australian dolphins: they all show distinct cultural practices in the way they relate with one another, hunt or sing. Animals show personality and morality – elephants can be empathetic or insensitive, rats can be lovers of fair play, spiders can be bold or spineless, chipmunks can be extrovert or shy. Cockroaches have feelings, too, it turns out.
Even the hard facts are letting us down: at the moment, researchers know of only a handful of genes unique to humans; it's thought that, when the count is finished and the numbers are totted up, fewer than 20 of our 20,000 genes will be exclusively human.
It's ironic that biology's love of hard facts is what has delayed our discoveries about the things we share with animals. Darwin was quite convinced of animal personality, compassion and feelings. However, the 1882 publication of George Romanes's book Animal Intelligence, a schmaltzy anthology of readers' tales and anecdotes, sent scientists running from the subject, and it became taboo for nearly a century. That is why Jane Goodall suffered endless insults and derision for her assertions that chimps did not all behave the same way, and that they exhibited moods and personalities, went through childhood and adolescence and grieved at the deaths of their relatives.
One thing does set us apart: our linguistic abilities. These, however, are a quirk of evolution. Although nothing in the animal kingdom is using what we think of as language, gestures used by bonobos and orangutans come close. The fact that we have slightly different anatomical arrangements that allow us to speak is hardly a marker of a fundamental difference.
So we are top of the class, perhaps, but not in a class of our own. This understanding should lead us to re-examine the relationship we have with animals. It is already becoming clear that their personalities affect their ability to survive habitat change. A 2004 study of the three-spined stickleback found that the chemical ethinyl estradiol, which is contained in birth-control pills and has been found in significant concentrations in waterways around the world, makes female sticklebacks exhibit more risky behaviour. The result is lower survival times compared with those in unpolluted waters.
Our responsibility goes beyond habitat pollution and destruction. Our discoveries mean we are already changing the way (and extent to which) we experiment on animals. The next step may be more far‑reaching: how comfortable would we be, for instance, eating a lobster that we knew was terrified by its capture?

2014年6月22日 星期日

Without Shannon's information theory there would have been no internet

Without Shannon's information theory there would have been no internet

It showed how to make communications faster and take up less space on a hard disk, making the internet possible
Shannon’s information theory
Shannon’s information theory
This equation was published in the 1949 book The Mathematical Theory of Communication, co-written by Claude Shannon and Warren Weaver. An elegant way to work out how efficient a code could be, it turned "information" from a vague word related to how much someone knew about something into a precise mathematical unit that could be measured, manipulated and transmitted. It was the start of the science of "information theory", a set of ideas that has allowed us to build the internet, digital computers and telecommunications systems. When anyone talks about the information revolution of the last few decades, it is Shannon's idea of information that they are talking about.
Claude Shannon was a mathematician and electronic engineer working at Bell Labs in the US in the middle of the 20th century. His workplace was the celebrated research and development arm of the Bell Telephone Company, the US's main provider of telephone services until the 1980s when it was broken up because of its monopolistic position. During the second world war, Shannon worked on codes and methods of sending messages efficiently and securely over long distances, ideas that became the seeds for his information theory.
Before information theory, remote communication was done using analogue signals. Sending a message involved turning it into varying pulses of voltage along a wire, which could be measured at the other end and interpreted back into words. This is generally fine for short distances but, if you want to send something across an ocean, it becomes unusable. Every metre that an analogue electrical signal travels along a wire, it gets weaker and suffers more from random fluctuations, known as noise, in the materials around it. You could boost the signal at the outset, of course, but this will have the unwanted effect of also boosting the noise.
Information theory helped to get over this problem. In it, Shannon defined the units of information, the smallest possible chunks that cannot be divided any further, into what he called "bits" (short for binary digit), strings of which can be used to encode any message. The most widely used digital code in modern electronics is based around bits that can each have only one of two values: 0 or 1.
This simple idea immediately improves the quality of communications. Convert your message, letter by letter, into a code made from 0s and 1s, then send this long string of digits down a wire – every 0 represented by a brief low-voltage signal and every 1 represented by a brief burst of high voltage. These signals will, of course, suffer from the same problems as an analogue signal, namely weakening and noise. But the digital signal has an advantage: the 0s and 1s are such obviously different states that, even after deterioration, their original state can be reconstructed far down the wire. An additional way to keep the digital message clean is to read it, using electronic devices, at intervals along its route and resend a clean repeat.
Shannon showed the true power of these bits, however, by putting them into a mathematical framework. His equation defines a quantity, H, which is known as Shannon entropy and can be thought of as a measure of the information in a message, measured in bits.
In a message, the probability of a particular symbol (represented by "x") turning up is denoted by p(x). The right hand side of the equation above sums up the probabilities of the full range of symbols that might turn up in a message, weighted by the number of bits needed to represent that value of x, a term given by logp(x). (A logarithm is the reverse process of raising something to a power – we say that the logarithm of 1000 to base 10 – written log10(1000) – is 3, because 103=1000.)
A coin toss, for example, has two possible outcomes (or symbols) – x could be heads or tails. Each outcome has a 50% probability of occurring and, in this instance, p(heads) and p(tails) are each ½. Shannon's theory uses base 2 for its logarithms and log2(½) is -1. That gives us a total information content in flipping a coin, a value for H, of 1 bit. Once a coin toss has been completed, we have gained one bit of information or, rather, reduced our uncertainty by one bit.
A single character taken from an alphabet of 27 has around 4.76 bits of information – in other words log2(1/27) – because each character either is or is not a particular letter of that alphabet. Because there are 27 of these binary possibilities, the probability of each is 1/27. This is a basic description of a basic English alphabet (26 characters and a space), if each character was equally likely to turn up in a message. By this calculation, messages in English need bandwidth for storage or transmission equal to the number of characters multiplied by 4.76.
But we know that, in English, each character does not appear equally. A "u" usually follows a "q" and "e" is more common than "z". Take these statistical details into account and it is possible to reduce the H value for English characters to less than one bit. Which is useful if you want to speed up comms or take up less space on a hard disk.
Information theory was created to find practical ways to make better, more efficient codes and find the limits on how fast computers could process digital signals. Every piece of digital information is the result of codes that have been examined and improved using Shannon's equation. It has provided the mathematical underpinning for increased data storage and compression – Zip files, MP3s and JPGs could not exist without it. And none of those high-definition videos online would have been possible without Shannon's mathematics.

2014年6月19日 星期四

訪問 美國《科學》主編 (董潔林)

2014/06/18 10:13:48


更多忽東忽西的文章 »

從另一方面來說,由於全世界學者發論文需求強勁而國際頂級學術期刊成為極度短缺的奢侈品,因此受到了科研工作者的尖銳批評。基於與一些研究自然科學和社會科學的同事們在這方面的討論,最近我書面訪談了世界頂級學術期刊美國《科學》雜志主編Marcia McNutt博士。McNutt博士很坦誠地回答了學者群體對頂級學術刊物的批評,闡述了她對科研界一些流行的不良行為的看法,並給中國科研者提出了誠懇的建議。下面是對話的完整內容:


McNutt:《科學》認識到優秀論文的數量已經增長了,由於一直受到我們每年預計印刷頁數的局限,我們發表這些傑出研究成果的能力沒有跟上來。因此,最近我們推出了一個嶄新的網上數字版期刊──《科學進步》(Science Advances),這個平台讓我們可以發表更多傑出的研究成果,唯一的要求就是投遞的文章必須是高質量的。另外,《科學進步》 會接受來自更廣泛的學術領域的文章,例如工程、技術以及那些與自然科學有密切聯系和對自然科學有影響的社會科學等。為了服務更多的讀者,這個新期刊採用開放獲取方式發行。

董潔林:在2013年12月,諾貝爾獎獲得者Randy Schekman教授發表了一篇題為“《自然》、《細胞》、《科學》等期刊正在如何損害科學”的文章。該文對這些頂級期刊的主要批評為:其一,“這些期刊精心策劃他們的品牌以達到更多銷售刊物的目的,而不是為了推動最重要的科學研究”;其二,“這些排他性的期刊為自己裝飾了一個名為“影響因子”的噱頭……這些奢侈期刊的編輯深諳此道,因此他們喜歡接受那些內容性感、結論有爭議能夠興風作浪的論文。這種做法影響了科學家的研究選題,推動一些時髦領域形成科研泡沫,而其他一些重要的工作則被耽誤了……” 你們對此如何回應?


《科學》曾多次公開指責“期刊影響因子”作為衡量文章質量這種做法。我們的前任主編Bruce Alberts簽署了“科研評估舊金山宣言”(The San Francisco Declaration on Research Assessment (DORA)),該宣言的目標是停止使用“期刊影響因子”來判斷科學家的工作。另外,Bruce Alberts先生還寫過一篇題為“影響因子的扭曲”的文章),他在文中特別提到了影響因子的誤用,他說:“期刊影響因子的誤用很有破壞性,玩指標遊戲會導致一些期刊不去發表一些重要但少被引用的論文。DORA提出的辦法對於保障科研健康至關重要。”















Marcia McNutt博士給中國科研工作者的建議讓人深思。科學研究和做產品很不一樣,做產品的人可以懷著偏心和圖利的態度去竭力推銷,而做科學則必須用客觀、理性和開放的態度探索科學真理,並將這個過程的細節公之於眾。發現真理本身,而不是其他,是對科研人員最大的獎勵。然而,她的簡單建議對一個浮躁的、系統性地以功利作為激勵手段的社會來說,是個容易的小調整,還是個不可能完成的任務?


2014年6月16日 星期一

英美齒科的革命研究: Regenerating teeth : An enlightened approach

No more fillings as dentists reveal new tooth decay treatment

Scientists in London develop pain-free filling that allows teeth to repair themselves without drilling or injections
The new treatment, Electrically Accelerated and Enhanced Remineralisation (EAER), could be available within three years. Photograph: Hermes Morrison 2/Alamy
Scientists have developed a new pain-free filling that allows cavities to be repaired without drilling or injections.
The tooth-rebuilding technique developed at King's College London does away with fillings and instead encourages teeth to repair themselves.
Tooth decay is normally removed by drilling, after which the cavity is filled with a material such as amalgam or composite resin.
The new treatment, called Electrically Accelerated and Enhanced Remineralisation (EAER), accelerates the natural movement of calcium and phosphate minerals into the damaged tooth.
A two-step process first prepares the damaged area of enamel, then uses a tiny electric current to push minerals into the repair site. It could be available within three years.
Professor Nigel Pitts, from King's College London's Dental Institute, said: "The way we treat teeth today is not ideal. When we repair a tooth by putting in a filling, that tooth enters a cycle of drilling and re-filling as, ultimately, each 'repair' fails.
"Not only is our device kinder to the patient and better for their teeth, but it's expected to be at least as cost-effective as current dental treatments. Along with fighting tooth decay, our device can also be used to whiten teeth."
A spinout company, Reminova, has been set up to commercialise the research. Based in Perth, Scotland, it is in the process of seeking private investment to develop EAER.
The company is the first to emerge from the King's College London Dental Innovation and Translation Centre, which was set up in January to take novel technologies and turn them into new products and practices.
King's College is a participant in MedCity, a project launched by the London mayor, Boris Johnson, to promote entrepreneurship in the London-Oxford-Cambridge life sciences "golden triangle".
The chairman of MedCity, Kit Malthouse, said: "It's brilliant to see the really creative research taking place at King's making its way out of the lab so quickly and being turned into a new device that has the potential to make a real difference to the dental health and patient experience of people with tooth decay."


Regenerating teeth
An enlightened approach
It may be possible to stimulate decayed teeth to repair themselves May 31st 2014 |

Goodbye to all that

REGENERATIVE medicine is a field with big ambitions. It hopes, one day, to repair or replace worn-out hearts, livers, kidneys and other vital organs. Many people, though, would settle for a humbler repair—of their teeth.

Dentistry has too much “drill and fill”, cutting away infected tissue and replacing it with alien, artificial materials. But if work by people such as David Mooney of Harvard University comes to fruition, the days of drill and fill may be numbered. For, as they report in Science Translational Medicine, Dr Mooney and his team have found a surprising way to get dentine, the tissue that underlies a tooth’s enamel coat, to repair itself. They do so by shining a laser beam at it.

Regenerative medicine boils down to the intelligent manipulation of stem cells. A stem cell is one that has the capacity to split asymmetrically so that one daughter remains a stem cell (and can thus go on to perform the same trick) while the other gives birth to a line which proliferates and differentiates into many other sorts of cell. The most famous, and controversial, stem cells are those in early embryos. These can turn into any sort of body cell. Mature tissues such as dentine contain stem cells of more limited capability, which keep up a supply of new specialised cells to replace old ones as they die.

Dr Mooney’s trick is to tickle dentine’s stem cells in a way that encourages them to proliferate and produce more dentine. And that is where the laser comes in. The light it shines creates chemically potent, oxygen-rich molecules such as hydrogen peroxide which go on to activate latent versions of molecules called transforming growth factor–beta 1 (TGF-beta 1). These, in turn, activate dentine’s stem cells and encourage the tissue’s growth.

Dr Mooney and his team have shown that this works in both tissue cultures and actual (rats’) teeth. Moreover, blocking the action of TGF-beta 1 with a drug, or by knocking out the gene that encodes the growth factor’s receptor, stops it happening, which suggests they have understood the mechanism correctly.

This is a preliminary result, and it does not address the question of whether enamel might similarly be repaired. But it is encouraging. Eventually, perhaps, dentists will approach cavities with lasers rather than drills—and the days of fillings will be over. - See more at: http://www.economist.com/news/science-and-technology/21602989-it-may-be-possible-stimulate-decayed-teeth-repair-themselves-enlightened?fsrc=scn%2Ffb%2Fwl%2Fpe%2Fanenlightenedapproach#sthash.vhcWn7xZ.dpuf


Dentistry has too much "drill and fill", cutting away infected tissue and replacing it with alien, artificial materials. But if work by people such as David Mooney of Harvard University comes to fruition, the days of drill and fill may be numbered. Dr Mooney and his team have found a surprising way to get dentine, the tissue that underlies a tooth's enamel coat, to repair itself http://econ.st/1iz5skc

2014年6月14日 星期六

Earth's Rocks Contain a Hidden Ocean's Worth of Water

Earth's Rocks Contain a Hidden Ocean's Worth of Water

WASHINGTON — If you want to find Earth's vast reservoirs of water, you may have to look beyond the obvious places like the oceans and polar ice caps.
Scientists say massive amounts of water appear to exist deep beneath the planet's surface, trapped in a rocky layer of the mantle at depths between 250 and 410 miles (410 to 660 kilometers).
Fragments of a blue-colored mineral called ringwoodite can be synthesized in the laboratory. The mineral can include a significant amount of water in its crystal structure, deep below Earth's surface.
But do not expect to quench your thirst down there. The water is not liquid — or any other familiar form like ice or vapor. It is locked inside the molecular structure of minerals called ringwoodite and wadsleyite in mantle rock that possesses the remarkable ability to absorb water like a sponge.
"It may equal or perhaps be larger than the amount of water in the oceans," Northwestern University geophysicist Steve Jacobsen said Friday in a telephone interview. "It alters our thoughts about the composition of the Earth."
"It's no longer liquid water that we're talking about at these great depths. The weight of hundreds of kilometers of rock and very high temperatures above 1,000 degrees Celsius (1,832 Fahrenheit) break down water into its components. And it's not accessible. It's not a resource in any way," Jacobsen added.
Jacobsen said water is taken down into the mantle with minerals during the process known as plate tectonics — the slow, inexorable movement of the colossal rock slabs that make up the Earth's surface.
When the minerals containing this water reach certain depths, they break down in a process called dehydration and release the water to form magmas. Such "dehydration melting" is common in the shallow mantle and forms the source for magmas in many volcanoes.
In a study published in the journal Science, the researchers present evidence that this is also occurring much deeper in the mantle, in a region called the "transition zone" between Earth's upper and lower mantle.
The study combined lab experiments involving synthetic ringwoodite being exposed to conditions simulating the heat and pressure of the transition zone, and observations of events in this zone, based on seismic data from a network of more than 2,000 seismometers across the United States.
A team led by Jacobsen and University of New Mexico seismologist Brandon Schmandt identified deep pockets of magma, a likely signature of the presence of water at those depths.

— Will Dunham, Reuters


編譯中心 2014年06月13日 18:243577 點擊數
新墨西哥大學和西北大學的研究人員在《科學》(Science)雜誌上的報告說,這一「隱藏的海洋」位於地球內部410公里至660公里深處、上下地幔(mantle)之間的過渡帶(transition zone),其水分並不是一般熟悉的液態、氣態或固態,而是以水分子的形式存在於一種名為「林伍德石」(ringwoodite)的岩石中。
西北大學地球物理學家雅各布森(Steve Jacobsen)說:「我想我們最終找到了整個地球水循環的證據,這或許有助於解釋地球地表大量液態水的存在,幾十年來,科學家一直在尋找這一缺失的深層水。」