Geoscience Reference
In-Depth Information
true north, then wandered off, reaching 24 degrees west by 1823. Computer models can-
not explain it exactly, but suggest that the dynamo itself is fluctuating chaotically. Most of
the time, coupling with the mantle damps out the effects, but sometimes they get so great
that the field flips. What is not clear is whether the reversals happen virtually overnight or
whether there are thousands of years in which the field wanders wildly or virtually disap-
pears. If the latter is the case, it would be bad news not only for navigation by compass but
for life on Earth generally as it would be exposed to more hazardous radiation and particles
from space.
7. A possible model for the generation of the Earth's magnetic field. Convection cur-
rents in the outer core spiral due to Coriolis forces (ribbon arrows). That, and elec-
trical currents (not shown) produce the magnetic field lines (black arrows).
There have also been attempts to model what goes on in the Earth's core by experiment.
This is not easy since it requires a large volume of electrically conducting fluid circulating
with sufficient velocity to excite a magnetic field. It was achieved in Riga by German and
Latvian scientists who used 2 cubic metres of molten sodium contained in concentric cyl-
inders. By propelling the sodium down the central cylinder at 15 metres per second, they
were able to generate a self-exciting magnetic field.
