A new study led by researchers from the University of Oxford and MIT has provided the oldest estimate of the strength of Earth’s magnetic field, dating back to 3.7 billion years ago. The researchers examined ancient rocks from Isua, Greenland, which contain iron particles that act as tiny magnets, recording the strength and direction of the magnetic field when the rocks crystallized. They found that the magnetic field strength at that time was at least 15 microteslas, comparable to the current field strength of 30 microteslas.
This study is a significant step forward in understanding the early history of Earth’s magnetic field and its role in shaping the development of Earth’s atmosphere. The Earth’s magnetic field is generated by the mixing of molten iron in the fluid outer core, driven by changes in density as the inner core slowly solidifies. The results suggest that the mechanism driving Earth’s early dynamo was efficient, similar to the process that generates the current magnetic field.
The findings may also provide insights into the role of Earth’s magnetic field in atmospheric evolution, particularly regarding the escape of gases into outer space. A strong magnetic field can shield a planet’s atmosphere from solar wind, preventing the stripping away of gases, but it can also accelerate particles or atoms into space. Understanding the ancient strength and variability of Earth’s magnetic field can help determine its importance in hosting life on a planetary surface.
Researchers plan to further expand their knowledge of Earth’s magnetic field before the rise of oxygen in the atmosphere around 2.5 billion years ago by examining other ancient rock sequences in Canada, Australia, and South Africa. This research will help determine the role of planetary magnetic fields in the evolution of atmospheres and their possible importance for the existence of life on a planet’s surface.
While the magnetic field strength has remained relatively constant, it is known that the solar wind was stronger in the past when the young Sun was more active. This suggests that Earth’s surface was better protected from the solar wind over time, potentially allowing life to move onto continents and away from the protection of the oceans. The full research paper detailing the findings was published in the Journal of Geophysical Research: Solid Earth.
