COLIN STUART is the author of The Big Questions In
Science: The Quest To Solve The Great Unknownsdown by 30-40 per cent for the last 800,000
years,” says Gubbins. While its strength is
dropping dramatically now, we are coming off
the back of a particularly big high. So it might
be nothing to worry about.
This complex nature of the Earth’s magnetic
field means no-one knows for sure if we
are heading for an imminent reversal, an
excursion, or whether the current weakening is
a symptom of some other magnetic affliction.
“The closer we look at what’s going on, the
more complicated it becomes,” says Glatzmaier.
What is certain is that our magnetic field
has flipped hundreds of times throughout
our planet’s history, and one day it will flip
again. When it does, our magnetic defences
will be weakened, exposing us to greater
bombardment from dangerous space radiation.
However, unlike Mars, our magnetic field
is likely to bounce back, as it has countless
times before – Earth’s dynamo isn’t going to
switch off any time soon. At least we should be
thankful for that.happen twice as often as that. Yet the poles
haven’t reversed in the last 780,000 years. It is
possible they are finally beginning to do so.
Another possibility is that we are being
sold a dummy. “In between reversals you get
excursions. This is where the magnetic field
seems like it is beginning to flip, but it goes
back,” says Gubbins. An excursion occurs
when the orientation of the planet’s magnetic
field alters by up to 45 ̊. According to Gubbins
you typically get 10 excursions for every
reversal, and the last one happened around
23,000 years ago. The angle of the magnetic
field can change rapidly too. Studies of lava
layers on Steens Mountain in Oregon, USA,
have shown that it once varied by 6 ̊ per day.
What these studies of our planet’s ancient
magnetic field have shown is that it is
inherently variable. “It has been going up andIt is perhaps a sign that a magnetic anomaly
in the Earth’s core is increasing in stature. That
could be the reason why the overall strength
of the magnetic field is dropping, and it may
signal an oncoming reversal.
Time to flip?
A reversal is certainly long overdue
Geoscientists study the timings of past reversals
by analysing layers of volcanic lava built up
over millions of years. As lava cools, it takes
on some of the magnetic properties of the
ambient magnetic field. So locked up in this
ancient lava is information about which way
the magnetic field was pointing at the time.
According to these lava records, the average
gap between reversals is around 200,000 years.
Computer simulations of the core show it can
down by 30 -40 per cent for the last 800, 000
years,” s ays Gubbins. While its strength is
dropping dramatically now, we are coming off
the back of a particularly big high. So it might
be nothing to worry about.Gary Glatzmaier, Professor of Earth
and Planetary Sciences, University of
California, Santa Cruz“The closer we
look at what’s
going on, the more
complicated it
becomes”
Lava
fields on
Steens Mountain
have revealed that
the magnetic field
once shifted by
6 ̊ a day