We all know that Earth's magnet field is constantly changing in its direction and strength. It is fascinating to see how fast these changes are occurring, as this feature protects us from cosmic radiation.
A new analysis of ancient volcanic flows in eastern Scotland has confirmed previous research that the magnetic field experiences a 200-million year cycle. This is when it weakens, then strengthens.
To double-check measurements from the past few decades and chart a history Earth's magnetic field back 500 million years, the team used magnetic history buried in the geological records.
"Our findings, when compared with the existing datasets support the existence of an approximately 200 million-year-long cycle in Earth's strength of the Earth’s magnetic field related deep Earth processes," said Louise Hawkins, a paleomagnetist from the University of Liverpool.
"As nearly all our evidence of processes in the Earth's interior has been destroyed by plate tectonics," the preservation of this signal is extremely valuable as one of few constraints that we have.
On rock samples taken from ancient lava flows, microwave and thermal paleomagnetic analyses were performed. The alignment of mineral crystals within the rocks revealed the Earth's magnetic field state at the time of their formation.
The team found that the magnetic field had dipped between 332 million and 416 millions years ago. This dip matches up to the one that occurred 120 million years earlier. The earlier period, now known as the Mid-Palaeozoic Dipole Low (MPDL), saw Earth's magnetic field around 25% less than it is today.
These dates are consistent with the 200 million-year cycle and provide experts important new insight into how the magnetic fields behaved more than 300,000,000 years ago. This is the time leading up to the Superchron, a name that refers to an extended period when the field remains stable.
Hawkins says, "The comprehensive magnetic analysis of Kinghorn and Strathmore lava flows was crucial for filling up the period leading to the Kiman Superchron," Hawkins said.
If this cycle continues, and magnetic pole flips or reverses tend to occur every 200,000 to 300,000 years, then we are actually due for another one. Scientists worry about the impact on all the technology and gadgets that we don't have the last time.
We can better predict the future by knowing more about Earth's history and magnetic field. We need to be aware of any problems in our space radiation force field as soon as possible.
Another bonus result of the research was that it had been previously believed that flips in magnetic field orientation occur when the field strength is lower. This is another hypothesis that the new data supports.
Hawkins says that "our findings further support the notion that pole reversals are associated with weak magnetic fields, while superchrons have strong magnetic fields, which is important because it has been nearly impossible to improve our reversal record before around 300 million years."
The research was published in PNAS.
