An extremely important event for our existence on Earth has been recorded in ancient rocks.
According to Sci-News, a team of geologists led by the Massachusetts Institute of Technology (MIT, USA) and the University of Oxford (UK) has discovered the oldest evidence of Earth’s magnetic field formation in ancient rocks from the Isua Supergroup in West Greenland.
The Isua Supergroup in West Greenland has experienced three thermal events throughout its geological history.
Geologists are drilling ancient rocks in West Greenland to search for evidence of Earth’s oldest magnetic field – (Photo: MIT NEWS).
Among these, the first event was the most significant, where rocks were heated to 550 degrees Celsius about 3.7 billion years ago. This is how the ancient Earth generated its magnetic field.
The Earth’s magnetic field is created when molten iron in the outer core mixes with fluid, driven by buoyancy as the inner core solidifies, creating a gigantic “dynamo.”
This process provided the initially barren Earth with an invisible protective shield known as the magnetosphere.
The magnetosphere protects the planet’s surface from solar winds, which have increased over time. Thanks to this protective layer, life was able to move onto continents and step out from the protection of the oceans.
For example, a neighboring planet, Mars, while located in the “habitable zone” of the Solar System, has a magnetosphere that is too thin and weak to shield against harmful cosmic radiation. Therefore, Mars currently does not have Earth-like life.
Ancient data from the rocks in West Greenland also reveals that the magnetic field 3.7 billion years ago had an intensity of at least 15 microteslas. In comparison, the present Earth’s magnetic field has an intensity of 30 microteslas.
These results provide the oldest estimates of Earth’s magnetic field intensity derived from the entire rock sample, offering a more accurate and reliable assessment than previous studies that used individual crystals.
“This is a really significant step as we try to determine the role of the ancient magnetic field when life first emerged on Earth,” said Professor Claire Nichols from the University of Oxford (UK), a member of the research team.
A significant challenge in reconstructing the Earth’s magnetic field to date is that any event that heats the rocks can alter previously preserved signals.
Rocks in the Earth’s crust often have a long and complex geological history, erasing previous magnetic information.
However, the Isua Supergroup has unique geology, sitting on a thick continental crust that protects it from tectonic activity and widespread deformation, thus preserving the integrity of ancient magnetic data.
This data comes from iron grains in the rocks, effectively acting as tiny magnets that can record both the intensity and direction of the magnetic field when crystallization locks them in place.
The results also provide new insights into the role of the magnetic field in shaping the development of Earth’s atmosphere.
The magnetosphere helps regulate the planet’s atmosphere by pushing certain gases into space and preventing the loss of essential elements, thereby maintaining balance in the atmosphere, which is another necessity for life.
