Polarity Reversal: Schematic illustration of Earth’s magnetic field.
Photo Credit: Peter Reid, The University of Edinburgh
The earth’s magnetic poles are moving; this is a regular occurrence and it has happened a number of times since the earth’s formation as a planet. Continuous measurements have been made of the earth’s magnetic field since about 1840, with some stand-alone measurements dating to the 1500s—one being at Greenwich in London. The earth has revered its magnetic field about 170 times over the last 100 million years; the last time was about 780,00 years ago:
NASA writes about this phenomena:
Reversals are the rule, not the exception. Earth has settled in the last 20 million years into a pattern of a pole reversal about every 200,000 to 300,000 years, although it has been more than twice that long since the last reversal. A reversal happens over hundreds or thousands of years, and it is not exactly a clean back flip. Magnetic fields morph and push and pull at one another, with multiple poles emerging at odd latitudes throughout the process. Scientists estimate reversals have happened at least hundreds of times over the past three billion years. And while reversals have happened more frequently in "recent" years, when dinosaurs walked Earth a reversal was more likely to happen only about every one million years.This is noteworthy; the earth’s magnetic field is weakening, which suggests to some scientists that we might eventually see a reversal, where soon is less than 2,000 years, a short period in cosmological time. The British Geological Survey says the earth might be in the early stages of such a reversal, which would take at least a few hundred years to take full effect;
If we look at the trend in the strength of the magnetic field over this time (for example the so-called 'dipole moment' shown in the graph below) we can see a downward trend. Indeed projecting this forward in time would suggest zero dipole moment in about 1500-1600 years time. This is one reason why some people believe the field may be in the early stages of a reversal. We also know from studies of the magnetisation of minerals in ancient clay pots that the Earth's magnetic field was approximately twice as strong in Roman times as it is now.So, what are the implications of a weakening magnetic field and a possible reversal of its polarity? Nothing dramatic, really; no doomsday scenario to offer you, NASA says:
Many doomsday theorists have tried to take this natural geological occurrence and suggest it could lead to Earth's destruction. But would there be any dramatic effects? The answer, from the geologic and fossil records we have from hundreds of past magnetic polarity reversals, seems to be 'no.'This is important to point out for the reason that ancient man viewed such phenomena, a change of some magnitude, as a “work of the gods.” Now that we know more about the natural order of things—through the use of scientific observations and record-keeping—and how nature operates, we can view such changes as a pattern of events that take place in some predictable fashion. This kind of knowledge makes us less fearful as human beings. And, perhaps, less superstitious.