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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 swings.
However, the Earth’s magnetic field collapsed nearly 591 million years ago, and this change may, paradoxically, have played a central role in the flowering of complex life, according to new research.
“In general, the area is protected. If we didn’t have a field early in Earth’s history water would have been removed from the planet by the solar wind (a stream of energetic particles flowing from the sun towards the Earth),” said John Tarduno, professor of Geophysics at the National University of Ireland. Galway. Rochester in New York and senior author of the new study.
“But in the Ediacaran, we had a very interesting period in the development of the deep earth when 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 the Earth’s magnetic field, which is created by the motion of molten iron in the Earth’s outer core, was much weaker than its current strength for a period At least 26 million. years. The discovery of the ongoing weakening of the Earth’s magnetic field also helped solve an enduring geological mystery about when the Earth’s solid inner core formed.
This time frame coincides 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 were hardly like modern life – squash fans, tubes and doughnuts, and discs like Dickinsonia, which grew up to 4.6 feet (1.4 meters) in size, and the slug like Kimberella .
Before this, life was mostly unicellular and microscopic. The researchers believe that a weak magnetic field could have led to an increase in oxygen in the atmosphere, making early complex life possible.
Close exposure to the collapse of the magnetic field
The strength of the Earth’s magnetic field is known to change over time, and the crystals held in rock contain tiny magnetic particles that lock a record of the strength of the Earth’s magnetic field.
The first evidence that the Earth’s magnetic field weakened significantly during this period came in 2019 from a study of 565 million year old rocks in Quebec which suggested that the field was 10 times weaker than today at the that point.
The latest study corroborated more geological evidence showing that the magnetic field had weakened significantly, with information in the 591-million-year-old rock from a site in southern Brazil suggesting that the field was 30 times weaker than as it is today.
The magnetic field wasn’t always so weak: the team examined similar rocks from South Africa dating back more than 2 billion years and found that, at that time, the 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 generated.
“Over billions of years that process is becoming less and less effective,” he said.
“And by the time we get to the Ediacaran, the field is on its last legs. It is almost collapsing. But luckily for us it got cool enough that the inner core started generating (strengthening the magnetic field).”
The emergence of the earliest complex life that would have roamed the seabed at this time is associated with a rise in oxygen levels. Some animals can survive at low levels of oxygen, such as sponges and microscopic animals, but larger animals with more complex bodies that move need more oxygen, Tarduno said.
Traditionally, the increase in oxygen during this time has been attributed to photosynthetic organisms such as cyanobacteria, which produced oxygen, allowing it to build up in the water steadily over time, explained study coauthor Shuhai Xiao , professor of geobiology at Virginia Tech.
However, the new research suggested an alternative, or complementary, hypothesis involving an increased loss of hydrogen in space when the geomagnetic field was weak.
“The magnetosphere protects the Earth from the solar wind, so the atmosphere keeps with the Earth. Therefore, a weaker magnetosphere means that lighter gases such as hydrogen would be lost from the Earth’s atmosphere,” Xiao said via email.
Tarduno said multiple processes could be going on at the same time.
“We do not challenge that one or more of these processes were occurring simultaneously. But the weak field may have allowed oxygen to cross a threshold, helping the radiation of animals (evolution),” said Tarduno.
Peter Driscoll, a staff scientist at the Earth and Planetary Laboratory at the Carnegie Institution for Science in Washington, DC, said he agreed with the findings of the study regarding the weakness of the Earth’s magnetic field, but the claim that the weak magnetic field could affect have on the oxygen of the atmosphere. and biological evolution was difficult to assess. He was not involved in the study.
“It is difficult for me to assess the truth of this claim because the potential influence of planetary magnetic fields on climate is not well understood,” he said via email.
Tarduno said her hypothesis was “solid,” but it could take years of challenging work to establish a causal link because of how little is known about the animals that lived at this time.
Inner heart mystery
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 been solid – when iron first crystallized in the center of the planet – range from 500 million to 2.5 billion years ago.
The research into the strength of the Earth’s magnetic field suggests that the age of the Earth’s inner core is on the younger side of that time scale, solidifying after 565 million years ago and allowing the Earth’s magnetic shield to bounce back.
“The observations seem to support the claim that the nuclear inner core first formed soon after this time, pushing the geodynamo (the mechanism that creates the magnetic field) from a weak unstable state to a strong dipole field,” said Driscoll.
Tarduno said that the recovery of the strength of the field after the Ediacaran, with the growth of the inner core, was probably important to prevent the drying of the water-rich Earth.
As for the strange animals of the Ediacarans, they all disappeared in the following Cambrian Period, when the diversity of life exploded and the branches of the tree of life that we know today were formed in a relatively short time.
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