Earth's Magnetic Field Weakening
Around 600 million years ago, Earth's magnetic field experienced a dramatic collapse, triggering a global oxygenation event that accelerated the pace of evolution.
Recent research on ancient rocks from South Africa and Brazil indicates that Earth's magnetic field weakened significantly approximately 591 million years ago. This period, known as the Ediacaran Period (635 million to 541 million years ago), witnessed a significant increase in atmospheric and oceanic oxygen levels, enabling the emergence of larger, more mobile organisms than seen in previous life forms.
Oxygen Activation and Evolutionary Milestone
The findings suggest that the magnetic field's weakening allowed oxygen to become more active, leading to a surge in evolutionary advancements.
"If this is true, then this is a profoundly deep event in evolution," said lead researcher and planetary scientist John Tarduno of the University of Rochester in New York.
These discoveries provide insights into how life may have flourished on other planets and underscore the profound impact of Earth's geology on our planet's atmosphere and surface processes.
Earth's Magnetic Field Formation and Decline
Earth's magnetic field is generated by the motion of its iron-rich core. Today, this field is driven by the convection of a liquid outer core surrounding a solid inner core. This convection is fueled by heat released from the crystallizing solid core, growing at a rate of about 1 millimeter per year.
However, before the solid inner core became as large and rigid as it is today, Earth's magnetic field was powered by convection in a molten core that extended through the mantle. Over time, the core cooled and solidified, and the temperature gradient between the core and mantle decreased, leading to reduced heat flow, convection, and a weakened magnetic field.
Erasing the Magnetic Field
The new study posits that the magnetic field nearly vanished 591 million years ago, becoming 30 times weaker than today. Scientists determined this by examining the magnetic field preserved in ancient rock crystals formed beneath the Earth's surface.
Rocks that are 2 billion years old exhibit a magnetic field as strong as the present-day field. This suggests that the heat flow from Earth's molten core began declining near the start of the Ediacaran Period, with the field reaching a low point during the Ediacaran.
At some point, the field may have disappeared entirely, but the processes driving the magnetic field then restarted as Earth's core solidified, gradually re-establishing the field.
Oxygenation and Field Collapse
The 26-million-year period of magnetic field weakness coincides with the Ediacaran oxygenation event, and the connection may not be coincidental.
The magnetic field surrounds Earth like a protective blanket, but at the north and south poles, the field lines extend into space. When the magnetic field is weak, these polar openings become larger. This gap allows hydrogen molecules to escape into space. Fewer hydrogen molecules mean fewer molecules for oxygen to bond with, leading to more free oxygen in the atmosphere and oceans.
This sudden abundance of oxygen presented an opportunity for organisms to grow larger and become more mobile.
Earth may have been fortunate that the magnetic field weakening did not persist for too long. If the field had remained weak, the increased exposure to space would have stripped Earth of its water.
"We need the Earth's magnetic field to retain water on our planet," said Tarduno. "The curious thing is that during the Ediacaran, the fact that the magnetic field was weak actually helped evolution."
Summary
Approximately 600 million years ago, a collapse in Earth's magnetic field allowed oxygen to become more active, leading to a surge in evolutionary advancements. The magnetic field's weakening may have been temporary, but its impact on the planet's oxygen levels and subsequent evolution was profound, shaping the trajectory of life on Earth.