BBC NEWS Americas Africa Europe Middle East South Asia Asia Pacific
BBCi NEWS   SPORT   WEATHER   WORLD SERVICE   A-Z INDEX     

BBC News World Edition
 You are in: Science/Nature  
News Front Page
Africa
Americas
Asia-Pacific
Europe
Middle East
South Asia
UK
Business
Entertainment
Science/Nature
Technology
Health
-------------
Talking Point
-------------
Country Profiles
In Depth
-------------
Programmes
-------------
BBC Sport
BBC Weather
SERVICES
-------------
EDITIONS
Wednesday, 2 October, 2002, 12:17 GMT 13:17 UK
Quakes reveal 'core within a core'
Core, BBC,PNAS
Scientists probing the secrets of the Earth's inner core say there is evidence of another, smaller, core hidden within it.

If they are correct, it could reveal more about how the Earth itself formed.

The inner core was first discovered in the 1930s, and scientists have been looking ever since for ways to measure it.

It is solid, about 2,440 km across, and composed mainly of iron and nickel.

A new way of measuring the composition of the core was found when the shock-waves from earthquakes on one side of the world were measured by sensors on the opposite surface.


Trying to understand how the Earth evolved is one of the fundamental problems we have in science

Professor Guy Masters, Scripps Institute
To get there, they would have had to pass through the centre, and it proved possible to measure subtle changes to the speed of the waves depending on what kind of rocks and minerals they encountered on their route.

Bizarrely, a wave travelling from north to south moved faster than one going east to west.

It is believed that this effect happens because the core has been formed in a crystalline manner - with its components lining up in the same direction, changing the speed at which the waves pass through depending on their initial direction.

This phenomenon is called anisotropy.

Tough centre

The latest research, published in the Proceedings of the National Academy of Sciences (PNAS), found that a wave precisely targeted through the inner core behaved differently depending on which part of the core it travelled through.

There appeared to be a separate "inner inner" core - perhaps 600 km in diameter.

Not only was the anisotropy effect much stronger - suggesting an even more crystalline composition - but the angle of most resistance, a guide to the alignment of these crystals, was different to that of the rest of the inner core.

Researchers from Harvard University, US, used data from more than 300,000 seismic events between 1964 and 1994.

They believe that this difference may be the result of changes in the environment of the core during its formation.

As such, further studies may be able to shed some extra light on how, and at which point, the core was formed.

The researchers said that, with more seismometers in place around the world, it might be possible to complete a more detailed survey of the core.

Attention grabber

Professor Guy Masters, from the Scripps Institute of Oceanography in San Diego, US, told BBC News Online that, if the findings were correct, the "core within a core" could be left over from an early stage of the planet's formation.

He said: "This would change the way we think about the formation of the inner core.

"If it's right, we have to explain it somehow.

"Trying to understand how the Earth evolved is one of the fundamental problems we have in science.

"The core is just so strange that it seems to catch people's attention."

See also:

21 Feb 01 | Science/Nature
02 Mar 01 | Science/Nature
15 Jan 02 | Science/Nature
27 May 02 | Science/Nature
23 Jan 02 | Africa
Internet links:


The BBC is not responsible for the content of external internet sites

Links to more Science/Nature stories are at the foot of the page.


E-mail this story to a friend

Links to more Science/Nature stories

© BBC ^^ Back to top

News Front Page | Africa | Americas | Asia-Pacific | Europe | Middle East |
South Asia | UK | Business | Entertainment | Science/Nature |
Technology | Health | Talking Point | Country Profiles | In Depth |
Programmes