(Press-News.org) The iron in the Earth's inner core weakens dramatically before it melts, explaining the unusual properties that exist in the moon-sized solid centre of our planet that have, up until now, been difficult to understand.
Scientists use seismic waves - pulses of energy generated during earthquakes - to measure what is happening in the Earth's inner core, which at 6000 km beneath our feet is completely inaccessible.
Problematically for researchers, the results of seismic measurements consistently show that these waves move through the Earth's solid inner core at much slower speeds than predicted by experiments and simulations.
Specifically, a type of seismic wave called a 'shear wave' moves particularly slowly through the Earth's core relative to the speed expected for the material – mainly iron – from which the core is made. Shear waves move through the body of the object in a transverse motion - like waves in a rope, as opposed to waves moving through a slinky spring.
Now, in a paper published in Science, scientists from UCL have proposed a possible explanation. They suggest that the iron in the Earth's core may weaken dramatically just before melting, becoming much less stiff. The team used quantum mechanical calculations to evaluate the wave velocities of solid iron at inner-core pressure up to melting.
They calculated that at temperatures up to 95% of what is needed to melt iron in the Earth's inner core, the speed of the seismic waves moving through the inner core decreases linearly but, after 95%, it drops dramatically.
At about 99% of the melting temperature of iron, the team's calculated velocities agree with seismic data for the Earth's inner core. Since independent geophysical results suggest that the inner core is likely to be at 99-100% of its melting temperature, the results presented in this paper give a compelling explanation as to why the seismic wave velocities are lower than those predicted previously.
Professor Lidunka Vočadlo, from the UCL department of Earth Sciences and an author of the paper said: "The Earth's deep interior still holds many mysteries that scientists are trying to unravel.
"The proposed mineral models for the inner core have always shown a faster wave speed than that observed in seismic data. This mismatch has given rise to several complex theories about the state and evolution of the Earth's core."
The authors stress that this is not the end of the story as other factors need to be taken into account before a definitive core model can be made. As well as iron, the core contains nickel and light elements, such as silicon and sulphur.
Professor Vočadlo said: "The strong pre-melting effects in iron shown in our paper are an exciting new development in understanding the Earth's inner core. We are currently working on how this result is affected by the presence of other elements, and we may soon be in a position to produce a simple model for the inner core that is consistent with seismic and other geophysical measurements. "
###
Notes to Editors
1. For more information or to speak to Professor Lidunka Vočadlo, please contact Clare Ryan in the UCL Media Relations Office on tel: +44 (0)20 3108 3846, mobile: +44 (0)7747 565 056, out of hours +44 (0)7917 271 364, e-mail: clare.ryan@ucl.ac.uk.
2. 'Strong pre-melting effect in the elastic properties of hcp-Fe under inner-core conditions' will be published in Science at 2:00 PM US Eastern Time on 10 October 2013.
3. The work was funded by a Natural Environment Research Council (NERC) grant.
About UCL (University College London)
Founded in 1826, UCL was the first English university established after Oxford and Cambridge, the first to admit students regardless of race, class, religion or gender and the first to provide systematic teaching of law, architecture and medicine.
We are among the world's top universities, as reflected by our performance in a range of international rankings and tables. According to the Thomson Scientific Citation Index, UCL is the second most highly cited European university and the 15th most highly cited in the world.
UCL has nearly 27,000 students from 150 countries and more than 9,000 employees, of whom one third are from outside the UK. The university is based in Bloomsbury in the heart of London, but also has two international campuses – UCL Australia and UCL Qatar. Our annual income is more than £800 million.
http://www.ucl.ac.uk | Follow us on Twitter @uclnews | Watch our YouTube channel YouTube.com/UCLTV
Iron in the Earth's core weakens before melting
2013-10-11
ELSE PRESS RELEASES FROM THIS DATE:
Kissing helps us find the right partner -- and keep them
2013-10-11
What's in a kiss? A study by Oxford University researchers suggests kissing helps us size up potential partners and, once in a relationship, may be a way of getting a partner to stick around.
'Kissing in human sexual relationships is incredibly prevalent in various forms across just about every society and culture,' says Rafael Wlodarski, the DPhil student who carried out the research in the Department of Experimental Psychology at Oxford University. 'Kissing is seen in our closest primate relatives, chimps and bonobos, but it is much less intense and less commonly used. ...
Newly discovered gene regulator could precisely target sickle cell disease
2013-10-11
Boston, Mass., October 10, 2013 – A research team from Dana-Farber/Boston Children's Cancer and Blood Disorders Center and other institutions has discovered a new genetic target for potential therapy of sickle cell disease (SCD). The target, called an enhancer, controls a molecular switch in red blood cells called BCL11A that, in turn, regulates hemoglobin production.
The researchers—led by Daniel Bauer, MD, PhD, and Stuart Orkin, MD, of Dana-Farber/Boston Children's—reported their findings today in Science.
Prior work by Orkin and others has shown that when flipped ...
European hunter-gatherers and immigrant farmers lived side-by-side for more than 2,000 years
2013-10-11
Hunter-gatherers and immigrant farmers lived side-by-side for more than 2,000 years in Central Europe, before the hunter-gatherer communities died out or were absorbed into the farming population.
In a paper published today in Science, researchers describe their analysis of DNA and isotopes from human bones found in the 'Blätterhöhle' cave near Hagen in Germany, where both hunter-gatherers and farmers were buried.
The team, led by anthropologist Professor Joachim Burger of the Johannes Gutenberg University, Germany, used stable isotopes to determine their diet, DNA ...
Study finds no increased risk of suicide in patients using smoking cessation drugs
2013-10-11
A study to assess whether patients prescribed smoking cessation drugs are at an increased risk of suicide, self-harm and treated depression compared with users of nicotine replacement therapy (NRT) has found no evidence of an increased risk. The findings, led by researchers from the University of Bristol, are published online in the British Medical Journal [BMJ] today [11 October].
Varenicline (brand name Champix in the UK, Chantix in the US) is widely used by patients seeking to stop smoking with recent figures showing there were one million prescriptions for the drug ...
New antiviral response discovered in mammals
2013-10-11
Many viral infections are nipped in the bud by the innate immune response. This involves specific proteins within the infected cell that recognize the virus and trigger a signalling cascade – the so-called interferon response. This activates a protective mechanism in neighbouring cells and often results in the death of the primarily infected cell.
In plants and invertebrates another mechanism is known to function in antiviral immune response: the so-called RNA interference (RNAi) pathway. RNAi uses an intermediate of the viral proliferation process to build a weapon against ...
Hunter-gatherers and immigrant farmers lived together for 2,000 years in Central Europe
2013-10-11
Indigenous hunter-gatherers and immigrant farmers lived side-by-side for more than 2,000 years in Central Europe, before the hunter-gatherer communities died out or adopted the agricultural lifestyle. The results come from a study undertaken by the Institute of Anthropology at Johannes Gutenberg University Mainz (JGU) that has just been published in the eminent journal Science. A team led by Mainz anthropologist Professor Joachim Burger studied bones from the 'Blätterhöhle' cave near Hagen in Germany, where both hunter-gatherers and farmers were buried. "It is commonly ...
U of M researchers suggest complex relationship between phosphorus levels and nitrogen removal in lakes
2013-10-11
In the land of 10,000 lakes, one lake has been the starting place for research with implications for big lakes around the world. According to a study published online this week in Science, University of Minnesota researchers, building from studies of nitrogen levels in Lake Superior, uncovered a good news/bad news scenario for lake health that has long-term, global implications for pollution control efforts.
While many water-quality cleanup efforts focusing on the reduction of phosphorus have been highly effective, that success can also result in a decrease in microbial ...
Sticks and stones: Brain releases natural painkillers during social rejection, U-M study finds
2013-10-11
ANN ARBOR, Mich. — "Sticks and stones may break my bones, but words will never hurt me," goes the playground rhyme that's supposed to help children endure taunts from classmates. But a new study suggests that there's more going on inside our brains when someone snubs us – and that the brain may have its own way of easing social pain.
The findings, recently published in Molecular Psychiatry by a University of Michigan Medical School team, show that the brain's natural painkiller system responds to social rejection – not just physical injury.
What's more, people who ...
Scientists shed light on the brain mechanisms behind a debilitating sleep disorder
2013-10-11
Normally muscles contract in order to support the body, but in a rare condition known as cataplexy the body's muscles "fall asleep" and become involuntarily paralyzed. Cataplexy is incapacitating because it leaves the affected individual awake, but either fully or partially paralyzed. It is one of the bizarre symptoms of the sleep disorder called narcolepsy.
"Cataplexy is characterized by muscle paralysis during cognitive awareness, but we didn't understand how this happened until now, said John Peever of the University of Toronto's Department of Cell & Systems Biology. ...
Ancient DNA reveals multiple stages of settlement in Europe
2013-10-11
WASHINGTON—Research conducted by the National Geographic Genographic Project, a multiyear global initiative that uses DNA to map the history of human migration, is helping unravel the timing and source of human settlement in Central Europe.
New ancient-DNA research led by the National Geographic Society's Genographic Project, the Australian Centre for Ancient DNA (ACAD) and researchers from the University of Mainz in Germany and the State Heritage Museum in Halle (Germany) showed a pattern of genetic replacement taking place across several millennia in a region of central ...