Number 244 (Story #3), October 11, 1995 by Phillip F. Schewe and Ben Stein FLIPPING EARTH'S MAGNETIC FIELD has been accomplished, at least inside a computer. Gary Glatzmaier of Los Alamos and Paul Roberts of UCLA used 2000 CPU hours on a Cray C- 90 to simulate 40,000 years in the life of our planet's interior. The job included solving numerically the nonlinear equations describing the movements of Earth's fluid outer core repeatedly for 2 million time intervals. Some geologists believe the motion of the electrically conducting core constitutes the dynamo that generates terrestrial magnetism. Signs of gigantic shifts in the geodynamo, including complete reversals, are present in the geologic record, and so it was reassuring to see such a reversal during the computer simulation. The researchers expect to run longer simulations and hope to see several reversals. (Nature, 21 September 1995.)