A recent study conducted by the University of Oxford and MIT has successfully recovered a 3.7-billion-year-old record of Earth’s magnetic field, which appears to be remarkably similar to the field surrounding Earth today. Published in the Journal of Geophysical Research, the findings shed light on the importance of Earth’s magnetic field in shielding the planet from harmful cosmic radiation and charged particles emitted by the Sun. This protection is essential for the survival of life on Earth, making the study particularly significant.
By examining ancient iron-containing rocks from Isua, Greenland, the researchers were able to analyze the magnetic field strength and direction from 3.7 billion years ago. Iron particles within these rocks act as tiny magnets that record the magnetic field when they become locked in place during the crystallization process. The results revealed that the magnetic field strength at that time was at least 15 microtesla, comparable to the modern strength of 30 microtesla. This provides the oldest estimate of Earth’s magnetic field strength derived from whole rock samples, offering a more accurate assessment compared to previous studies using individual crystals.
Lead researcher Professor Claire Nichols expressed excitement about the challenge of extracting reliable records from rocks of such ancient age. She emphasized the importance of understanding the role of the ancient magnetic field during the emergence of life on Earth, highlighting the significance of these findings. While the magnetic field strength has remained relatively constant over time, the study suggests that the protection from the solar wind has increased, potentially facilitating the movement of life onto continents from the oceans.
The study also contributes to understanding the formation of Earth’s inner, solid core and the processes involved in heat escaping from the planet’s deep interior. The researchers faced challenges in reconstructing Earth’s magnetic field due to potential alterations in preserved signals caused by geological events heating the rocks. However, the unique geology of the Isua Supracrustal Belt allowed for the preservation of magnetic field information from 3.7 billion years ago. This opens up new avenues for further research into the role of Earth’s magnetic field in shaping the development of the planet’s atmosphere.
Insights from this study may also provide clues to explain the loss of unreactive gases such as xenon from Earth’s atmosphere over 2.5 billion years ago. Researchers are beginning to explore the possibility that the magnetic field played a role in the removal of charged xenon particles from the atmosphere. Future research aims to expand our knowledge of Earth’s magnetic field prior to the rise of oxygen in the atmosphere around 2.5 billion years ago. By examining ancient rock sequences in various locations around the world, scientists hope to gain a better understanding of the ancient strength and variability of Earth’s magnetic field, shedding light on its importance for hosting life on a planetary surface.
