Within Earth's interior, the molten material that makes up the outer core flows around the inner core in the opposite direction of the Earth's rotation. This "dynamo" is believed to be responsible for generating Earth's magnetosphere, the intrinsic magnetic field that shields life on the surface from harmful radiation. But since the flow of molten material in Earth's core isn't perfectly stable, the magnetosphere ebbs and flows over time. Scientists also theorize that this field prevents Earth's atmosphere from being slowly stripped away by charged solar particles (solar wind), which is believed to have been the case with Mars.
As a result, Earth's magnetic field is theorized to be integral to Earth's habitability, though its role in maintaining the atmosphere remains an ongoing field of study. According to new research by a team of NASA scientists, changes in Earth's magnetic field over the past 540 million years are correlated to fluctuations of oxygen levels in our atmosphere. Their research suggests that processes in Earth's interior might be directly connected to changes in our atmosphere, which could have significant implications for our understanding of planetary habitability.
The study was led by Weijia Kuang, a geophysicist at the Geodesy and Geophysics Laboratory and Sellers Exoplanet Environments Collaboration (SEEC) at NASA’s Goddard Space Flight Center. She was joined by researchers from NASA Goddard's Planetary Environments Laboratory, the Department of Earth and Space Sciences/Astrobiology Program at the University of Washington, and the School of Earth and Environment at the University of Leeds. The paper describing their findings appeared on June 13th in Science Advances.
Artist's impression of Earth's interior structure. Credit: Science Photo Library
Earth scientists have long known that the history of Earth's magnetic field is recorded by magnetized minerals in rocks. When magma rises to the surface and solidifies, the minerals retain indications of the magnetic field it formed in and how strong it was. As long as the minerals are not heated to the point that they become molten again, this magnetic record can remain intact indefinitely. Similarly, the chemical composition of rocks and minerals is dependent on the amount of oxygen in which they formed, allowing scientists to determine how oxygen levels rose and fell over time. As Kuang said in a NASA press release:
These two datasets are very similar. Earth is the only known planet that supports complex life. The correlations we’ve found could help us to understand how life evolves and how it’s connected to the interior processes of the planet.
Geophysicists and geochemists have compiled extensive records on both magnetism and oxygen levels, as recorded in ancient rocks. But according to the authors, there have been no detailed comparisons between these records before. When Kuang and his colleagues analyzed the two datasets, they found that fluctuations in Earth's magnetic field correlated with rising and falling levels of atmospheric oxygen since the Cambrian Explosion. This event, which occurred about 540 million years ago, is when complex life and practically all major animal phyla started to appear in the fossil record. Coauthor Benjamin Mills, a biogeochemist at the University of Leeds added:
This correlation raises the possibility that both the magnetic field strength and the atmospheric oxygen level are responding to a single underlying process, such as the movement of Earth’s continents.
The research team hopes to examine more datasets to test this correlation. This will include datasets that look back farther than the Cambrian Era, as well as those that catalog changes in other atmospheric components (like nitrogen) that are essential to life. These studies could reveal a vital connection between the interior dynamics of planets and habitability, which could also have implications for the search for life beyond Earth (astrobiology).
