Inside the Earth

Mt. St. Helens is erupting. Last week there was an earthquake in California. The Earth below our feet is seething. Where is this heat coming from? Well, the same force that tethers us to the Earth has caused not only this heat but also the fires in the sun itself, and in all stars. The force of gravity.

Four and a half billion years ago a cloud of gas and dust drifted through space. It was cool, hundreds of degrees below zero. Nudged by a star exploding nearby, it began to contract. As it contracted, it heated up. The core of that cloud became so hot that a nuclear fire began there and our sun was born.

The gravity that contracted the cloud was the true source of the fire in the sun!

At the outer reaches of the cloud, giant spheres of molten rock began to condense out of the cloud. Third from the sun, one of these spheres is destined to become the Earth.

Exposed to the coldness of space, a thin crust forms on the outside of the Earth, like the skin forming on the top of a warm pudding. But inside the Earth is still seething, a reminder of the awesome temperatures of the cloud that gave us birth.

The crust on which we live -- the ground beneath our feet -- is thin. Compared with the vast bulk of the Earth, it is thinner than the skin of a balloon.

This crust is cracked. One piece is the continent we live on. Others are the floor of the Pacific and the floor of the Atlantic. These pieces crash into each other. Sometimes they fold under the enormous pressure and produce mountains. When they cannot fold to relieve the pressure, the Earth quakes.

But what's most terrifying is what's happening under Mt. St. Helens right now. The crust there is so thin that it cannot hold back the titanic force of the molten rock within. From time to time the molten rock breaks through. The volcano erupts.

(10/08/04)