It comes as no surprise to Southern Californians that solid Earth moves. But until recently, geologists believed that these periodic rumblings were mostly skin-deep.

Outbreaks such as earthquakes, volcanoes and violent weather were confined to the surface, like a bad complexion. Hidden beneath the layers of crust and mantle, they felt, the planet had an inner serenity.

New insights into the world down under, however, have unearthed an unexpected hotbed of activity:

* Thousands of miles down, continent-sized formations build up and break apart, much as they do on the surface.

* Currents of rock rise, fall and churn like weather patterns--albeit at a slower pace.

* Iron crystals rain toward the core, piling into drifts like snow.

* Magnetic field lines twisted into cyclones somehow produce the neat North and South magnetic poles used by navigators around the world to set their compasses. Every hundred thousand years or so, the poles flip--and South becomes North.

All these discoveries are rearranging geologists' ideas about how the Earth works, and how it came to be. Evidence is now overwhelming that the planet did not come gently into being, but rather was part of a primordial storm throughout the solar system that blew the crust off Mercury, slammed into Venus hard enough to reverse its spin, and ripped the moon out of the Earth like Adam's rib.

Today, the leftover heat of that violent era--still buried deep in the Earth's core--drives mountain building, volcanoes and earthquakes.

"It's a major paradigm shift," said UC Berkeley geophysicist Raymond Jeanloz, who notes that as recently as the 1970s, geologists did not accept the idea that continents drift around on the mantle's Plasticine sea.

Jeanloz, a MacArthur "genius" Fellow, specializes in what he argues is the most geologically active region on Earth. It can be found, he said, "about three days' drive straight down, if you could do it."

Jeanloz's research leads him to believe that the thin layer between the Earth's core and the overlying mantle is the most dramatic structure on the planet.

Although the core lies a mere 1,740 miles from the surface, it is a world as remote and inaccessible as the planet Pluto. Digging a hole to the center isn't an option because the pressure gets so intense even a few miles down that the Earth instantly heals itself, filling in any hole before it gets very deep.