The near-collapse of Earth’s magnetic field 591 million years ago may have allowed the development of complex life | CNN

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The Earth’s magnetic field plays a key role in making our planet habitable. The protective bubble above the atmosphere protects the planet from solar radiation, winds, cosmic rays and wild temperature fluctuations.

However, Earth’s magnetic field almost collapsed 591 million years ago, and this change, surprisingly, may have played a key role in the flourishing of complex life, according to new research.

“In general, the field is protective. “If we didn’t have a field early in Earth’s history, water would have been stripped from the planet by the solar wind (a stream of energetic particles flowing from the sun to Earth),” said John Tarduno, professor of geophysics at the University of Rochester. in New York and senior author of the new study.

“But in the Ediacaran, we had an exciting period in the development of the deep Earth, when the processes that created the magnetic field … had become so ineffective after billions of years that the field almost completely collapsed.”

The study, published in the journal Communications Earth & Environment on May 2, found that Earth’s magnetic field, which is created by the movement of molten iron in Earth’s outer core, has been significantly weaker than its current strength for at least 26 million years. The discovery of the continuous weakening of Earth’s magnetic field also helped solve an enduring geological mystery about when Earth’s solid inner core formed.

This time frame aligns with a period known as the Ediacaran, when the first complex animals appeared on the sea floor as the percentage of oxygen in the atmosphere and ocean increased.

These strange animals bore almost no resemblance to life today – pumpkin fans, pipes and donuts, and disks like Dickinsonia, which grew up to 1.4 meters in size, and the sloth Kimberella.

Before this time, life was largely single-celled and microscopic. The researchers believe that a weak magnetic field may have led to an increase in oxygen in the atmosphere, allowing early complex life to evolve.

Shuhai Xiao/Virginia Tech

A photo shows a cast of a 560-million-year-old Dickinsonia costata fossil found in South Australia. At more than a meter long, the creature is the largest known animal of that period.

Earth’s magnetic field strength is known to fluctuate over time, and crystals preserved in rock contain tiny magnetic particles that lock in a record of Earth’s magnetic field strength.

The first evidence that the Earth’s magnetic field weakened significantly during this time came in 2019 from a study of 565-million-year-old rocks in Quebec, which showed that the field was 10 times weaker than it is today at that point .

The latest study gathered more geological evidence to suggest that the magnetic field weakened dramatically, with information contained in a 591-million-year-old rock from a site in southern Brazil suggesting the field was 30 times weaker than today.

The weak magnetic field wasn’t always this way: The team examined similar rocks from South Africa dating back more than 2 billion years and found that, at that time, Earth’s magnetic field was as strong as it is today.

Unlike now, Tarduno explained, back then the innermost part of the Earth was liquid, not solid, affecting the way the magnetic field was created.

“Over billions of years this process becomes less and less efficient,” he said.

“And by the time we get to the Ediacaran, the field is on its last legs. It’s almost falling apart. But then, luckily for us, it cooled enough that the inner core started building up (strengthening the magnetic field).

The appearance of the earliest complex life that would have sprung up along the seafloor at this time is associated with rising oxygen levels. Some animals can survive in low oxygen levels, such as sponges and tiny animals, but larger animals with more complex bodies that move around need more oxygen, Tarduno said.

Traditionally, the increase in oxygen during this period has been attributed to photosynthetic organisms such as cyanobacteria, which produced oxygen, allowing it to accumulate in the water steadily over time, explained study co-author Shuhai Xiao, professor of geobiology at Virginia Tech.

However, the new research suggested an alternative or complementary hypothesis involving increased loss of hydrogen to space when the geomagnetic field was weak.

“The magnetosphere protects the Earth from the solar wind, thus keeping the atmosphere on Earth. So a weaker magnetosphere means that lighter gases like hydrogen will be lost from Earth’s atmosphere,” Xiao added via email.

Tarduno said several processes could be taking place at the same time.

“We do not dispute that one or more of these processes were occurring simultaneously. But the weak field may have allowed oxygenation to cross a threshold, helping animal radiation (evolution),” Tarduno said.

Peter Driscoll, a scientist at the Earth and Planets Laboratory at the Carnegie Institute for Science in Washington, said he agreed with the study’s findings about the weakness of Earth’s magnetic field, but the claim that the weak magnetic field could have affected the atmospheric oxygen and biological evolution was difficult to assess. He didn’t bother to study.

“It is difficult for me to assess the accuracy of this claim because the effect that planetary magnetic fields can have on climate is not very well understood,” he said via email.

Tarduno said their case was “robust,” but proving a causal link could take decades of painstaking work, given how little is known about the animals that lived at the time.

Shuhai Xiao/Virginia Tech

A fossil of a 565-million-year-old Ediacaran animal called Fractofusus misrai was found in the Fault Point Formation in Canada’s Newfoundland.

The geological analysis also revealed telling details about the innermost part of the Earth’s center.

Estimates of when the planet’s inner core may have solidified — when iron first crystallized in the planet’s center — once ranged from 500 million to 2.5 billion years ago.

Research into the strength of Earth’s magnetic field suggests that the age of Earth’s inner core is at the younger end of this time scale, solidifying after 565 million years ago and allowing Earth’s magnetic shield to bounce back.

“The observations seem to support the contention that the inner core first nucleated shortly after this interval, pushing the geoforce (the mechanism that creates the magnetic field) from a weak, unstable state to a strong, stable dipole field,” Driscoll said.

Tarduno said that the recovery of the field strength after the Ediacaran, with the development of the inner core, was probably important in preventing the drying of the water-rich Earth.

As for the strange Ediacaran animals, they had all but disappeared by the following Cambrian period, when the diversity of life exploded and the branches of the tree of life we ​​know today were formed in a relatively short period of time.

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