Earth’s Magnetic Field Nearly Collapsed 600 Million Years Ago. Then, Weird and Complex Life Evolved

Earth’s magnetic field sustains life on our planet, protecting us from solar winds, radiation and extreme changes in temperature. But around 591 million years ago, it almost collapsed. According to a new study, this near-disaster may have actually been the key to a burst of evolution, which paved the way for larger and more varied life forms to develop.

Published in the journal Communications Earth & Environment this month, the study found that a drastic weakening of Earth’s magnetic field that lasted for 26 million years corresponded with a period of the planet’s history called the Ediacaran. During this time, a large amount of oxygen in Earth’s atmosphere and oceans allowed for the first multicellular, oxygen-using organisms to arise from the sea.

The creatures that evolved during the Edicaran hardly resembled anything seen today, however, taking on disc-like forms and shapeless masses—some of which exceeded three feet in size. These fronds and fans include Earth’s earliest known animals, such as the blob-like Dickinsonia.

Scientists theorize that without the protection of the magnetic field roughly 600 million years ago, solar radiation pounded the Earth’s atmosphere, stripping away hydrogen and other light gases from the atmosphere. This left behind an abundance of free-floating oxygen atoms for organisms to use.

“If we’re right, this is a pretty profound event in evolution,” lead author John Tarduno, a geophysicist at the University of Rochester, tells Stephanie Pappas of Live Science.

Building on previous research that pointed to historical fluctuations in the magnetic field, the team of researchers examined rocks containing crystals that cooled over tens or hundreds of thousands of years. Now, these structures act as time capsules, evidencing the strength of the magnetic field at various points in Earth’s development.

An analysis of feldspar from southern Brazil revealed that 591 million years ago, the magnetic field was 30 times weaker than it is now. But two-billion-year-old rock from South Africa suggested that at that time, the magnetic field held the same strength it does today.

Then, Earth’s core was liquid, not solid. The liquid inner core churned as it released heat into the cooler mantle, moving molten iron around the core and enabling Earth’s magnetic field to exist. By the Ediacaran, this difference in temperature had decreased, reducing the movement of the core and, consequently, the presence of the magnetic field.

“By the time we get to the Ediacaran, the field is on its last legs,” Tarduno explains to CNN’s Katie Hunt. “It’s almost collapsing. But then, fortunately for us, it got cool enough that the inner core started to generate [strengthening the magnetic field].”

The new findings also shed light on a long-standing question: At what point did the Earth’s core solidify? Previous estimates ranged from 2.5 billion to 500 million years ago, but the team’s analysis places the event on the more recent end of that spectrum, closer to 565 million years ago. The solidification of the inner core was also a crucial event for the evolution of life—it allowed Earth’s magnetic field to regain its strength and protect the planet’s water from being entirely eroded by solar radiation.

“We need the Earth’s magnetic field to preserve water on the planet,” Tarduno tells Live Science. “But it is sort of an interesting twist that during the Ediacaran, the really weak magnetic field may have helped accelerate evolution.”

Previously, the scientific consensus held that photosynthesizing organisms like cyanobacteria created the surplus of oxygen during the Ediacaran, and it accumulated in the oceans over time, study co-author Shuhai Xiao, a geobiologist at Virginia Tech, writes to CNN.

The new findings don’t necessarily disprove this idea—instead, they might show the Earth gained oxygen in multiple ways.

“We do not challenge that one or more of these processes was happening concurrently. But the weak field may have allowed oxygenation to cross a threshold, aiding animal radiation [evolution],” Tarduno says to CNN.

David Dunlop, a physicist at the University of Toronto who was not involved in the research, tells Dino Grandoni of the Washington Post that while the recent work needs further study, the analyses were “impeccably done.”

“The hypothesis, although obviously speculative as any ideas about the earliest origins of life must be, seems worth a close look,” Dunlop tells the publication. “Causality is always hard to prove, but I am all for new ideas being put out for public scrutiny. It provokes further study and that is all to the good.”

Tara Wu | | READ MORE

Tara Wu is a freelance writer based in the northeastern U.S. and a former editorial intern with Smithsonian magazine. She covers science, society, culture and their intersection.