Earth's core creates life's shield

Impact: A `far-fetched' movie exaggerates chaos from loss of the planet's magnetic field.

Medicine & Science

March 24, 2003|By Frank D. Roylance | Frank D. Roylance,SUN STAFF

The Earth's core has inexplicably stopped spinning, causing a breakdown of the global magnetic field that has sheltered life from deadly solar and cosmic radiation for billions of years.

Flocks of birds fly into buildings. Pacemaker wearers drop dead in the streets. Super-charged lightning batters the planet. The government mounts a desperate mission to tunnel more than 1,800 miles into the Earth to jump-start the stalled core and restore the planet's magnetic shield before all life is extinguished. ...

OK, it's only a movie. It's called The Core, and it opens Friday in area theaters. But how much of the sci-fi thriller is science, and how much is fiction?

"It's far-fetched, but it's clever," said Johns Hopkins University geophysicist Peter Olson, who recently screened the film. No mission -- not even one led by a handsome geophysicist and a beautiful astronaut -- could reach Earth's core, he said, much less affect its motion. The deepest we've drilled is 7 miles.

But the astonishing reality is that the Earth's protective magnetism really is weakening, and it's happening 10 times faster than if the core had stopped spinning, as it does in the movie.

Don't start worrying, though. Here's what we know:

The Earth has a spherical inner core of solid iron, about two-thirds the size of the moon. It's surrounded by an outer core of liquid iron -- at 9,000 degrees Fahrenheit. Between the core and us is 1,800 miles of rock.

Scientists believe a planet's magnetic field is sustained by the circulation of its liquid outer core. The liquid iron flows generally east to west, in a motion complicated by heat-driven convection and many eddies.

The motion creates nature's equivalent of a dynamo -- a sort of generator in which the rotating liquid sustains the magnetic field. If the core stops or solidifies, the field fades away, which has happened on Venus, Mars and our moon.

The magnetic force field that shields all life extends tens of thousands of miles into space. It deflects or captures most of the atomic particles and dangerous radiation streaming from the sun, as well as cosmic rays from interstellar space.

If Earth's core stopped spinning today, it could take 20,000 years for the magnetic field to die away, Olson said. But "what we actually see is a much more rapid decay than that," almost 9 percent since Karl F. Gauss first measured the field in 1835.

At that rate -- about 6 percent per century -- its strength would be halved in about 1,000 years. In The Core, the geomagnetic field unravels in months, causing special-effects havoc.

Increased radiation from space and electrical changes in the atmosphere stop watches and melt suspension cables on the Golden Gate Bridge like an overloaded fuse. Lightning bolts blast the Colosseum to rubble.

It's all based on a particle of truth, Olson said, "but they took the actual phenomena as we currently understand them and exaggerated everything."

In real life, the loss of the Earth's magnetic field would have more gradual effects, from the curious to the catastrophic.

If the field shut down today, solar particles and radiation would stream into the atmosphere, creating worldwide auroras of a kind now seen only near the poles. More would penetrate to the ground.

"You wouldn't see it, but you would be exposed to more radiation," Olson said. Radiation injuries and genetic mutations would mount. Some say the atmosphere itself might erode, and the planet would eventually become uninhabitable.

The Earth's geomagnetic field has weakened substantially many times in the past 3 billion years, Olson said. But it has always maintained at least 10 percent of its current strength, and the hazard has always been brief, a few thousand years.

It occurs with intermittent reversals in the direction of the field, when Earth's magnetic poles swap positions -- north to south, south to north. Geophysicists can read the timing, strength and direction of those ancient magnetic fields in old lava and sedimentary rock.

By one count, 171 pole reversals have occurred in the past 71 million years. Over the past 5 million years, Olson said, it's averaged once every 250,000 years. But intervals have ranged from thousands of years to millions.

Paleontologists have tried to match pole reversals with great extinctions evident in the fossil record. But "no one has been able to establish a convincing correlation," Olson said.

The latest weakening is consistent with the start of a new pole reversal, Olson said. But nobody knows for certain.

"In a sense we are overdue," he said. The most recent reversal occurred about 750,000 years ago -- three times the average interval. On the other hand, "the field could turn and start growing again."

Geophysicists believe the problem is the South Atlantic Anomaly. Mapped by satellites, it's a giant pothole in the magnetic field off the coast of Brazil. Spacewalking astronauts and satellites flying through it get higher doses of radiation.

Olson said the anomaly may mark an "anti-dynamo" -- a reverse eddy in the flow of molten iron far below. If the trend continues into the next century, the field could weaken 20 percent.

"That's a little slow compared to the election cycle," he said. So expect no government mission to get the core flowing smoothly again. Except in the movies.

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