We know that the Earth's magnetic field is constantly changing its direction and strength. How quickly these changes occur is of great interest, given that this feature of the planet protects all of us from strong cosmic radiation.
A new analysis of ancient lava flows in eastern Scotland, filling some important gaps in the history of our magnetic field, has confirmed previous studies suggesting a 200-million-year cycle in which the field weakens and then intensifies again.
The team also used the magnetic history they found in the geologic record to double-check other measurements made over the past few decades and to map out the history of the Earth's magnetic field, which goes back about 500 million years.
"Our results, when considered along with existing data, confirm the existence of an approximately 200 million cycle in the strength of the Earth's magnetic field associated with deep earth processes," says paleomagnetologist Louise Hawkins of the University of Liverpool in the UK.
"Since almost all of our evidence of processes in the interior of the Earth is constantly being destroyed by plate tectonics, the preservation of this signal of deep earth processes is of immense value as one of the few evidence we have."
Methods of thermal and microwave paleomagnetic analysis were used to study rock samples from ancient lava flows, and the alignment of mineral crystals within them made it possible to determine the state of the Earth's magnetic field at the time of their initial formation.
The team found that between 332 and 416 million years ago, there was a sharp decline in power in the magnetic field, which coincides with another decline that occurred 120 million years ago. During an earlier period, now called the Middle Paleozoic Dipole Minimum (MPDL), the field surrounding the Earth was about a quarter stronger than it is today.
These dates coincide with the 200 millionth cycle and provide experts with important new insights into how the magnetic field behaved more than 300 million years ago, on the eve of a noticeable superchron - this is the name of the long period of time when the field remains stable.
"This comprehensive magnetic analysis of Strathmore and Kinghorn lava flows was key to filling the pre-Kiman superchron, a period when the geomagnetic poles are stable and unchanged for about 50 million years," Hawkins says.
If this cycle is correct, and reversals or reversals of the magnetic poles occur every 200,000-300,000 years, then another one awaits us - much to the concern of scientists who are not sure how this will affect all the technologies and gadgets that we clearly have was not last time
"The more we know about the history of the Earth's magnetic field as a whole, the better we can predict what it will do next. If our force field against cosmic radiation starts to experience problems, we need to know about it as soon as possible."
In the course of the study, another important conclusion was made: it was previously believed that changes in the orientation of the magnetic field occur when the field is weaker, and this is another hypothesis, which is supported by new data.
"Our results also provide additional confirmation that a weak magnetic field is associated with pole flips, while during a superchron, the field is usually strong, which is very important, since it turned out to be almost impossible to reconstruct the history of flips up to 300 million years ago," says Hawkins.
The study was published in the journal PNAS.