Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Elizabeth P. Crowe on 12/02/2011 00:30:03
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Elizabeth P. Crowe asked the Naked Scientists:
Dr. Chris:
I have some questions about the magnetic field of the Earth. I understand that it is responsible for deflecting some of the Sun's dangerous rays from the surface of the planet. I understand that occasionally, the geological record tells us, the poles will reverse. What I don't understand:
1. Why do the poles reverse? What is the physical cause?
2. Is this something that happens slowly, rather quickly, or suddenly? (Geologically speaking of course)
3. When they reverse, how does that affect the deflection of damaging rays from the Earth's surface? Is there a period where such rays are not deflected?
And just as an aside, should we ever colonize Mars, won't we have to live beneath the surface, because Mars has no magnetic field?
Thanks! Love the show! (http://www.thenakedscientists.com/HTML/podcasts/)
Elizabeth P. Crowe
What do you think?
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Scientists believe that the heat of the Earth's solid inner core heats a liquid outer core made primary of iron and nickel. The heating acts as a convection, generating electric currents and a magnetic field. Also the Earth turns which should destabilize the liquid 'dragging' it, along the angular motion induced. That makes for a chaotic system, also called a non-linear system. Such systems are known for their so called 'tipping's' which means that the system suddenly 'tips' from one, more or less, stable state to another. We're long overdue as we seem to have a tipping every 200,000 years as a average and as the last magnetic field tipping was 780,000 years ago, according to what we think us to know, studying the geologic records from lava etc that show us the magnetic field lines at some specific time period.
"Peter Olson, a geophysicist at Johns Hopkins University in Baltimore, Maryland, said scientists can now pinpoint the core-mantle boundary where these instabilities in the magnetic field are happening. One such disturbance Olson has been observing recently formed over the east-central Atlantic Ocean. Like a little hurricane, the anomaly swept toward the Caribbean and is moving up in the direction of North America.
"It's a new one, a little thing," Olson said. "Time will tell whether it develops into something significant. But it is here in the North Atlantic, moving towards the Pentagon. We can track it over the next couple of decades." Instabilities such as this, Olson added, are causing Earth's magnetic field to weaken. Today the field is about 10 percent weaker than it was when German mathematician Carl Friedrich Gauss first began measuring it in 1845. Some scientists speculate the field is headed for a reversal.
Rapid changes in the churning movement of Earth's liquid outer core are weakening the magnetic field in some regions of the planet's surface, a new study says. "What is so surprising is that rapid, almost sudden, changes take place in the Earth's magnetic field," said study co-author Nils Olsen, a geophysicist at the Danish National Space Center in Copenhagen.
The findings suggest similarly quick changes are simultaneously occurring in the liquid metal, 1,900 miles (3,000 kilometers) below the surface, he said. The swirling flow of molten iron and nickel around Earth's solid center triggers an electrical current, which generates the planet's magnetic field. The study, published recently in Nature Geoscience, modeled Earth's magnetic field using nine years of highly accurate satellite data.
Flip-Flop
Fluctuations in the magnetic field have occurred in several far-flung regions of Earth, the researchers found. In 2003 scientists found pronounced changes in the magnetic field in the Australasian region. In 2004, however, the changes were focused on Southern Africa.
The changes "may suggest the possibility of an upcoming reversal of the geomagnetic field," said study co-author Mioara Mandea, a scientist at the German Research Centre for Geosciences in Potsdam. Earth's magnetic field has reversed hundreds of times over the past billion years, and the process could take thousands of years to complete.
Upper Atmosphere Radiation
The decline in the magnetic field also is opening Earth's upper atmosphere to intense charged particle radiation, scientists say. Satellite data show the geomagnetic field decreasing in the South Atlantic region, Mandea said, adding that an oval-shaped area east of Brazil is significantly weaker than similar latitudes in other parts of the world.
"It is in this region that the shielding effect of the magnetic field is severely reduced, thus allowing high energy particles of the hard radiation belt to penetrate deep into the upper atmosphere to altitudes below a hundred kilometers (62 miles)," Mandea said. This radiation does not influence temperatures on Earth. The particles, however, do affect technical and radio equipment and can damage electronic equipment on satellites and airplanes, Olsen of the Danish space center said. The study documents just how rapidly the flow in Earth's core is changing, said Peter Olson, a geophysics professor at Johns Hopkins University in Baltimore, Maryland, who was not involved with the research.
By using satellite imagery, researchers have a nearly continuous measurement of changes, he said. "They provide a good rationale to continue this monitoring longer," Olson said. "
And no, it seems as if most of the time the changes are rather small, more seldom becoming a total reversal of the magnetic poles. But it's hard to study it on place as it's 6,400 kilometers or 4000 miles down under our feet, inside the Earth.
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Thank you! I understand a lot more now!
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Hi Elizabeth,
my name is Tyron Crowe. I live in Johannesburg, South Africa.
seeing another Crowe anywhere is pretty rare. I'm just curious if we're
possibly related. and if not, i suppose i"m really curious as to where
the Crowes come from originally. Here in SA, i think record-keeping has been very shoddy.
so, where do you live?
Mod edit :email removed .
Tyron, I have removed your email address to save you from receiving loads of spam. You can contact other members by using the personal message system.
Thanks
Neil