16 | NewScientist | 15 May 2010

ANCIENT pieces of continental crust that are falling to the bottom of the Earth’s mantle could explain mysterious dents in our planet’s gravitational field.

The Earth’s field is not uniform because of density variations inside the planet. Weaknesses in the field are believed to be created by “slab graveyards” – ancient pieces of crust and sediment that were pushed down into the Earth

when plates collided and are now falling through the mantle. The slabs are denser than the mantle and so have a stronger gravitational pull. As they fall, however, their effect on the field at the Earth’s surface decreases.

But surrounding these areas are even weaker, unexplained dents in the field. Now Sonja Spasojevic from the California Institute of Technology in Pasadena and

Eye-squint-cheek-bulge means ‘ouch’

THE facial expressions of mice can be used to assess the amount of pain they are in. Such discoveries could help animal workers such as vets detect physical discomfort in animals more reliably.

To identify the facial tics that indicate pain, Jeffrey Mogil of McGill University in Montreal, Canada and colleagues filmed mice for 30 pain-free minutes and then for 30 more after inducing mild pain.

They used this footage to draw up a “mouse grimace scale” based on changes in the face such as squinting eyes and bulging cheeks.

Mogil speculates that facial expressions may play a role in mouse communication, perhaps helping to warn others of danger. However, brief pain did not typically provoke a grimace. Mogil suggests that mice may be better off hiding momentary weakness from rivals (Nature Methods, DOI: 10.1038/nmeth.1455).

Earliest fossil bird held onto more than just its bones

IT BOASTS more than just beautiful impressions of long-gone feathers. One of the world’s most famous fossils – of the earliest known bird, Archaeopteryx – also contains remnants of the feathers’ soft tissue.

“It’s amazing that that chemistry is preserved after 150 million years,” says Roy Wogelius, a geochemist at the University of Manchester, UK. Wogelius and colleagues scanned the “Thermopolis specimen” using a powerful X-ray beam from a synchrotron at the Stanford Synchrotron Radiation Lightsource in California. The synchrotron excites atoms in target materials to emit

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Plumes of rock behind the Earth’s dents colleagues say this could be because the movement of the slabs forces plumes of less dense material towards the surface. The distribution of the unexplained weak spots simply reflects the pattern of these plumes (Nature Geoscience, DOI: 10.1038/ngeo855).

However, the density changes could occur in other ways, says Norm Sleep, a geophysicist at Stanford University in California. These include chemical reactions between the mantle and slabs.

X-rays at characteristic wavelengths. The scan reveals the distribution of elements throughout the fossil. The green glow of the bones in this false-colour image shows that Archaeopteryx, like modern birds, concentrated zinc in its bones. The red of the rocks comes from calcium in the limestone that has encased the fossil since the animal died (Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.1001569107).

Copper and zinc are key nutrients for living birds, and their presence in the fossil bones shows the evolutionary link with dinosaurs. The study also revealed phosphorous along the main shafts of the feathers in the fossil: palaeontologists had long thought that only impressions remained. “There is soft-tissue chemistry preserved in places where people didn’t expect it,” says Wogelius.

A NASAL spray made of the hormone vasopressin improves men’s ability to recognise the emotions of both happy and angry – but not neutral – faces.

Related “cuddle chemical” oxytocin improves bonding. So does vasopressin, but it also drives less cosy aspects of social behaviour, such as aggression.

So Adam Guastella at the University of Sydney in Australia compared the ability of 24 men given the spray to recognise neutral, angry and happy faces with peers given a placebo spray (Biological Psychiatry, DOI: 10.1016/j.biopsych.2010.03.014).

“There may be an application in people with inadequate recognition of social cues,” Guastella says.

Hormone boosts emotion detection

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