The Core: Hollywood Fiction or Science?

Chad Cohen
National Geographic Today
March 27, 2003
Deadly asteroid impacts, reincarnated killer dinosaurs, alien invasions. Just when you thought Hollywood had thrown it all at us, a fresh, new, end-of-the-world scenario opens in theaters tomorrow—this time the action is 4,000 miles (6,400 kilometers) below our feet in The Core.

It seems the core of the Earth has stopped spinning and is no longer generating the planet's protective magnetic field. This triggers a cascade of diabolical events for man and beast. Birds can't navigate and fly erratically into buildings. People with pacemakers unexpectedly drop dead. Massive electrical storms destroy all electronic communication, and unfettered blasts of solar radiation fry the planet.

And unless an intrepid team of "terranauts" journey to the center and start it spinning again, everyone on the planet will be dead within a year.

It has all the makings of a blockbuster…and it may not necessarily all be fantasy.

"I think of this movie as science faction more than science fiction," said Jon Amiel, director of The Core. "I think the audience will come out knowing a little more about the planet they're standing on."

The lead character in the film, himself a geophysicist, uses the anatomy of a peach to explain the different layers of the earth—the skin represents an average 18 miles (30 kilometers) of the rock-hard crust, the flesh 1,700 miles (2,800 kilometers) of semi-molten mantle. The pit serves as the core—4,350 miles (7,000 kilometers) across, about the size of Mars.

The core is subdivided into two layers—inner and outer. The inner core is thought to be a solid ball of iron and nickel about two-thirds the size of the moon while the outer layer is a giant ocean of liquid iron and nickel.

Magnetic Field Shutdown

Eddies and currents in this metallic outer ocean produce Earth's magnetic field. "At least we believe that, though we don't understand exactly what the mechanism is," said Richard Terrile, a planetary astronomer at the Jet Propulsion Laboratory in Pasadena, California, and a science consultant for the film.

So can the magnetic field really shutdown?

"In fact it has happened many times in the Earth's history," says Terrile. "The Earth's magnetic field is not a stable solid thing like a bar magnet—it actually changes, it moves directions, it goes up and down, and it actually reverses."

Don't throw away your compasses just yet. These shifts only occur every few hundred thousand years or so. But that's still enough to make the idea of a magnetic field shutdown at least plausible.

What would happen next is debatable even in scientific circles. In The Core, radioactive particles and microwave radiation literally cooks the planet. In one scene they even slice the Golden Gate Bridge in half.

"I don't want to diminish enthusiasm for the movie, but I don't think anybody would notice if the magnetic field disappeared," said Jack Connerney, a planetary scientist at Goddard Space Flight Center, in Greenbelt, Maryland.

"The ionosphere and atmosphere would keep out much of the solar wind and radiation," said Connerney, so although the radiation would increase slightly, life on Earth would not fry.

Connerney also doubts that huge electrical storms would be instantly generated. Both Venus and Mars lack global magnetic fields, he said. "We don't see strange electrical phenomena happening there."

Earth's Core A Natural Nuclear Reactor?

"Its hard to know what the effects on life will be. They've got to be devastating," said Marvin Herndon, a geophysicist based at the Transdyne Corporation in San Diego, California, another consultant for the movie. "It will short-circuit satellites, we'll have no ability to communicate with radio communications, and currents will be induced not only in electrical transmission lines…but railroad trains, bridges, gas pipelines."

As for what the "terranauts" encounter inside the earth, the moviemakers get little guidance from science.

"If you were to ask yourself which is the quickest way to the unknown, very clearly its straight down," said Terrile. "We know a lot more about almost everything else in the universe than we do about what's just a few miles below our feet."

To date, scientists have only been able to peer deep into the Earth indirectly, primarily by detecting the way sound bounces around during earthquakes—analogous to taking a giant CT scan of the planet.

The first really good image came from a massive earthquake in Chile in 1960.

"It was one of the biggest earthquakes on record and it really rang the core like a bell. A lot of understanding came from that earthquake," said Terrile.

But there is nothing to say that our understanding won't change. Earlier this month, Herndon published a radical new theory in Proceedings of the National Academy of Sciences that finds the Earth's inner core isn't just a giant iron-nickel ball as is commonly thought, but contains a ball of uranium only five miles (eight kilometers) in diameter—a natural nuclear reactor.

Herndon believes that this reactor will burn out sometime, be it in the next century or 1 billion years from now, killing the magnetic field.

"I think it could be worse than the movie portrays," Herndon said.

So as you munch your popcorn thinking that there is no way that this can happen, consider this: there is no guarantee that it won't.

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