Developments in Brief : Ancient Comet May Have Upset Things

A giant comet that slammed into Earth may have triggered a complex chain of events that caused the Earth’s magnetic field to temporarily reverse itself 700,000 years ago.

The effect would have caused compasses--had they existed--to point south instead of north, two University of California physicists at the Lawrence Berkeley Laboratory have written in a paper published in Geophysical Research Letters.

The report by researchers Richard A. Muller and Donald E. Morris contends that a comet, asteroid or giant meteor may have slammed into Earth, ultimately upsetting the motion of metals within the planetary core thousands of miles below the planet’s surface.

Consequently, the upsetting of the core could have led to the collapse or total reversal of the magnetic field, possibly for thousands of years.

Geologists detect past magnetic reversals by studying old rocks. When a rock forms, its metallic particles align themselves with the existing magnetic field, creating a “fingerprint” for the magnetic field of their era.

The alignments indicate the latest magnetic reversals occurred 700,000, 1.9 million and 2 million years ago.