Gate 2011 1.4

1.4 Variation of the geomagnetic field observed over the last 500 years indicates that the dipole moment of earth's the magnetic field has been

(A) decreasing

(B) increasing

(C) constant

(D) fluctuating randomly

Measurements taken from 1835 to 1965 reveal that the earth lost a whopping 8% in its magnetic field strength over those 130 years.) More recent measurements confirm this exponential rate of decrease, at a rate of about 1.5% every 30 years.) That means if you are 60 years old, in your own lifetime, the earth’s magnetic field decreased in strength by about 3%. 

When we look at the other planets of the Solar System, we find the same thing occurring. Our moon and Mars, for instance, used to have strong fields, but their fields have already died out, just like the earth’s is on the path to doing. 

When our probes visited Mercury (in 1975), not only did we discover it does have a field, on subsequent visits from our probes (up to 2011), we found its field is also exponentially decaying as well. So from 1975 to 2011, Mercury’s field decreased 7.8% in strength! 

One of the most awesome discoveries in all of this is that not only is the earth’s field decaying, but it is doing so at a precise exponential linear rate of decay. Not only that, but we have found a ‘little wobble’ (a precise sinusoid oscillation) in this rate of decay that further strongly implies “the cause of the decay is energy dissipation,” which is a death-knell to the old-earth dynamo model, which in turn means the earth is young: