The intensity of the earth’s magnetic field is constantly changing. It has dropped by 10-15% in the past century, which suggests that a geomagnetic reversal may occur. However, humans have not observed any of such events. Even though one was recorded in igneous rocks discovered a century ago, the transition time and detailed process are still elusive. Therefore, geomagnetic reversal was listed as one of the 125 unresolved science problems in 2005.
The limitations of observation time scale and inherent geological materials hinder humans from understanding the causes of reversal and the physical mechanism involved. Stalagmites used in the study can record simple geomagnetic information due to their continuous growth, which has been proven to reconstruct paleomagnetic field. The latest developments in sophisticated radioisotope dating and highly sensitive superconducting magnetometers enhance the use of stalagmites in such research.
The most challenging part of the research is to find stalagmites that contain sufficient magnetic minerals for paleomagnetic analysis. After ten years of searching, Prof. Shen’s team found an ideal stalagmite sample in southern China even though it only contains a small fraction of magnetic minerals and its magnetic strength is 1,000 times smaller than that of most igneous rocks. The team combined high-precision uranium-thorium radioisotope dating and high-sensitivity paleomagnetic analysis. 80 paleomagnetic data and 70 age control points were obtained to establish a reliable geomagnetic record of 16,000 years, which is from 107,000 to 91,000 years ago. The resolution of the record is dozens of years. The team discovered a reversal event occurred 98,000 years ago that spanned a hundred years. Compared with the fastest reversal speed in the past, the event is more than 10 times faster. If compared with the widely recognized transition time, it is shortened by more than 30 times.
In understanding the process of geomagnetic reversal, the team provides unprecedented timing accuracy and reveals the reversal speed that has not been discovered in the past. The study is merely a start. Other stalagmite records will further disclose the variability of the earth’s magnetic field and the reversal and shift of polarity.
Humans and their ancestors have lived on the earth for millions of years. In this period, there have been multiple polarity reversal. This, it does not mean that mankind survival will be challenged by such events. Yet, polarity transition can lead to serious chaos in ionosphere, atmosphere, and biosphere. Animals navigation, radio communication, satellites, and electronic power systems may suffer severe damage. Communication and transportation may be affected as well, which may include the Internet and stock markets.
To read the article: Multidecadally resolved polarity oscillations during a geomagnetic excursion