Biology Reference
In-Depth Information
TIME
Another essential context for properly reading Earth history is the accurate
measurement of geologic time, for which many methods are now available.
It has long been recognized that the center of the Earth is composed pri-
marily of molten iron in a constant state of motion that generates a mag-
netic force or geomagnetic energy. This energy fl ows to the surface near the
geographic South Pole, envelopes the Earth in a magnetic fi eld, and enters
back into the Earth near the North Pole. The process is of fundamental im-
portance to life on the planet because it provides a shield against the huge
amounts of lethal radiation emanating from the sun and transported through
the universe by the solar winds. The interaction between solar radiation
and the shield are manifested in the aurora borealis and aurora australis—
the northern and southern lights. What has not been recognized un-
til recently is that the Earth's magnetic fi eld has weakened by about
15 percent over the past 150 years, and at that pace it would be expected to
collapse in about 1000-1200 years.
The consequences of this weakening, if continued, would initially be a
disruption of radio- and satellite-based systems, a gradual increase in skin
cancers and genetic mutations, eventual extinctions, and ultimately a bar-
ren and lifeless planet. Such a scenario is given credence by preliminary
results of voyages to Mars indicating that millions of years ago it had a mol-
ten core, a geomagnetic fi eld, liquid water, and possibly some forms of life.
It is speculated that the present bleak and arid planet came about through
the weakening and then loss of the magnetic envelope due to cooling of the
molten core. Needless to say, this has generated interest beyond the fi eld of
astrophysics. However, there is encouraging new information that indicates
this worst-case scenario will probably not occur for quite a while. Earth is
larger than Mars, so its rate of cooling is slower, and any devastating effects
are likely to be millions of years in the future. Also, it is now known that
periodic weakening of the magnetic fi eld is part of a normal cycle, and that
these intervals are prelude not to imminent disaster but to another event of
considerable scientifi c importance.
Geomagnetic Reversals
On a highly variable time scale ranging from tens of thousands to tens of
millions of years, the Earth's magnetic fi eld reverses, with geomagnetic en-
ergy fl owing outward from near the North Pole and inward near the South
Pole. In fact, the magnetic North Pole is currently drifting to the south,
