Earth’s Magnetic Field Remained Weak for 40 Million Years
The prolonged period of geomagnetic instability followed the Cambrian explosion, reshaping our timeline of core evolution.
Updated on Oct. 16, 2026 in Geology
Geological evidence confirms that Earth’s magnetic field intensity entered a period of instability 750 million years ago, remaining weak for 40 million years after the Cambrian explosion. This historical research highlights that the planet's protective shield struggled during a critical era of early animal diversification.
Why it matters
Understanding the timeline of Earth's geodynamo stability is crucial for mapping the environmental conditions under which complex life emerged and evolved. The discovery suggests that early life flourished despite a significantly reduced magnetic shield, challenging previous assumptions about planetary habitability.
Researchers analyzed magnetic signatures from the Itabaiana Dike Swarm, formed 525 million years ago, alongside volcanic rock data from Nova Scotia. This record indicates that convection of liquid iron within the outer core resulted in frequent polarity reversals throughout this period.
The players
University of São Paulo
A Brazilian research institution focused on astronomy, geophysics, and atmospheric sciences that led the geological study.
University of Liverpool
An English university with an extensive Earth science department that provided collaborative support for the paleomagnetic analysis.
The details
The Earth's magnetic field is powered by the convection of liquid iron in the outer core, a process known as the geodynamo. By examining the Itabaiana Dike Swarm—a series of vertical volcanic rock formations in Brazil—scientists measured historical magnetic field intensity preserved in rock minerals. These samples, correlated with data from Nova Scotia, provide a proxy for the state of the planet’s magnetic shield during the early stages of animal life.
Timeline
750 million years ago: Earth's magnetic field began a sharp decline in intensity.
550 million years ago: The period when Earth's magnetic protection was hypothesized to be restored.
525 million years ago: The formation of the Itabaiana Dike Swarm in Paraíba, Brazil.
The Tech Race
This research provides a new benchmark for testing the hypothesis that inner core formation occurred around 550 million years ago. It establishes a clear geodynamic timeline that challenges existing models of how Earth's core cooling fueled the planet's magnetic recovery.
This finding does not affect current consumer technology or modern infrastructure. It serves exclusively as a fundamental update to the scientific understanding of Earth's early history.
The takeaway
The discovery clarifies that complex life thrived during a long-term period of geomagnetic instability. Researchers will continue to refine these models by sampling volcanic rocks from other formations to determine if these magnetic shifts were global or regional events.
Further reading
For more on the physical evolution of the planet, explore Geology.
Source note: This article includes information reported by Jornal da USP.
