Science: The Electric Earth

Washington’s Carnegie Institution, which does “significant research toward philosophical goals,” has been looking at the earth philosophically for several years. Last week its annual yearbook reported progress on some significant problems.

Earth Charge. Since 1917 scientists have known that the earth’s surface is charged with negative electricity, but no one knew for sure what keeps it charged. In areas of fair weather, an electric current flows between the earth and the air in a direction which would tend to dissipate the charge. It is not much of a current: only about 1,500 amperes, not much more for the entire earth than flows in a few power lines. But the electricity taken from the earth must be restored somehow or the earth’s electric charge would soon drain away.

An obvious guess is that thunderstorms somehow restore the lost charge, but no one had proved it. Three years ago the institution borrowed airplanes from the Air Force and began to measure electrical stirring in the still air above active thunderheads. Sure enough, the instruments showed a current moving in the opposite direction to the current in fair-weather areas. The scientists figured that all the thunderstorms going on at one time generate a net current of about 1,500 amperes, just enough to balance the drain and keep the earth’s charge constant.

Fossil Magnetism. The earth has a powerful magnetic field, but no one knows what creates it. In hope of finding out, the Carnegie scientists studied the magnetism in ancient sedimentary rocks.

When silt sinks slowly to the bottom of an ocean or lake, the magnetic particles in it line up with the earth’s magnetic field like tiny compass needles. When the silt hardens into rock, the magnetic particles are “frozen” so that they cannot move. The Carnegie scientists found that even when the rock layer is folded by geological forces, the magnetic particles keep their alignment, pointing accurately around the curves of the folds. Even in layers known to be 200 million years old, the rock keeps its magnetism.

Reassured by this stability, Dr. John Graham and a team of Carnegie geologists went to work. A series of rock samples 10 million to 100 million years old which they took from flat-lying strata in the western U.S. proved to have a magnetism pointing in about the same direction as present-day compass needles. The conclusion was that when the rocks were laid down as silt, the earth’s magnetic field was about as it is today.

But when the geologists examined rocks from Maryland more than 350 million years old, they found that their magnetism pointed in an entirely different direction. The south-seeking ends of the magnetic particles were pointing downward as the needles of “dip circle” compasses do in the southern hemisphere. The ancient Maryland rocks acted magnetically as if they had been formed nearer to the southern magnetic pole (in Antarctica) than to the northern one (in Canada).

The Carnegie scientists were cautious about jumping to conclusions. But at least two conclusions are possible: 1) that the earth’s magnetic field has shifted radically since 200 million years ago, or 2) that the North American continent, including Maryland, was once near the south pole and has since drifted slowly to its present position.