The planet's magnetic field played a key role in the emergence of life
More than 500 million years ago, strange, complex creatures appeared on Earth. Scientists now think they know why this happened.
The Earth's magnetic field plays a key role in making our planet habitable. A protective layer of the atmosphere protects the planet from solar radiation, winds, cosmic rays and sudden changes in temperature, CNN reports.
However, a new study found that 591 million years ago, the Earth's magnetic field almost completely collapsed, and this change is how this, paradoxically, could have played a key role in the blossoming of a complex life.
“Overall, the field is protective. If we didn't have a field early in Earth's history, water would have been blown away from the planet by the solar wind (a stream of charged particles moving from the Sun to Earth), says John Tarduno, professor of geophysics at the University of Rochester in New York and senior author. new research. “But in the Ediacaran period we had a fascinating stage in the development of the deep Earth, when processes occurred that created a magnetic field… Over billions of years, it became so ineffective 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 the Earth's outer core, has been significantly weaker than its current strength for at least 26 million years. The discovery of the persistent weakening of the Earth's magnetic field also helped solve a long-standing geological mystery about when the Earth's solid inner core formed.
This time frame coincides with the period known as the Ediacaran, when the very first complex animals appeared on the seafloor. as the percentage of oxygen in the atmosphere and ocean has increased, CNN explains.
These strange animals hardly resembled life today – soft fans, tubes and donuts, as well as discs such as Dickinsonia, which grew up to 1.4 meters in size, and the slug-like Kimberella.
Until this time life was mostly single-celled and microscopic. Researchers believe that a weak magnetic field may have increased oxygen levels in the atmosphere, allowing early complex life to evolve.
The strength of the Earth's magnetic field is known to fluctuate over time, and crystals preserved in rocks contain tiny magnetic particles that record the strength of the Earth's magnetic field.
The first evidence that the Earth's magnetic field has weakened significantly over time this period was derived in 2019 from a study of 565-million-year-old rocks in Quebec, which showed that the magnetic field at that time was 10 times weaker than today.
The latest study has collected additional geological data indicating a sharp weakening of the magnetic field, and information contained in a 591-million-year-old rock found in southern Brazil suggests the magnetic field was 30 times weaker than today.
The weak magnetic field wasn't always this way: the team examined similar rocks from South Africa that were more than 2 billion years old and found that the Earth's magnetic field was just as strong then as it is today.
Tarduno explained that, unlike today, the interior of the Earth was liquid rather than solid, which influenced the formation of the magnetic field.
“Over billions of years, this process becomes less and less efficient,” he says. “And by the time we get to Ediacara, the field is on its last legs.” It's almost collapsing. But then, fortunately for us, it became cold enough that the inner core began to generate (increasing the magnetic field).”
The emergence of the earliest complex life form that could appear on the seafloor at this time is associated with rising oxygen levels. Some animals can survive with low oxygen levels, 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 accumulate steadily in the water over time, explains study co-author Shuhai Xiao, a professor of geobiology at Virginia Tech.
However, a new study has put forward an alternative or additional hypothesis suggesting increased loss of hydrogen into space when the geomagnetic field is weak.
“The magnetosphere protects the Earth from the solar wind, thereby holding the atmosphere on the Earth. So a weaker magnetosphere means lighter gases such as hydrogen will be lost from Earth's atmosphere,” Xiao added via email.
Tarduno said multiple processes could be happening simultaneously.
Tarduno said there could be multiple processes going on at the same time.
Tarduno said there could be multiple processes going on at the same time.
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“We do not dispute that one or more of these processes occurred simultaneously. But the weak field may have caused oxygen saturation to cross a threshold, promoting animal radiation (evolution),” explains Tarduno.
Peter Driscoll, a staff scientist at the Earth and Planetary Laboratory at the Carnegie Institution for Science in Washington, D.C., says he agrees with the study's findings that Earth's magnetic field is weak, but the claim that a weak magnetic field could affect atmospheric oxygen and biological evolution is difficult to assess. He did not participate in the study.
“It’s difficult for me to assess the validity of this statement because the influence that the planet’s magnetic fields can have on climate is not very well understood,” the scientist said.
Tarduno said their hypothesis is “convincing,” but for proving a cause-and-effect relationship may require decades of complex work, given how little is known about the animals living at that time.
Geological analysis has also revealed interesting 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 at the planet's center—once ranged from 500 million to 2.5 billion years ago.
Studies of Earth's magnetic field strength suggest that age Earth's inner core is at the younger end of this time scale, having solidified after 565 million years ago and allowing Earth's magnetic shield to recover.
“The observations appear to support the claim that the inner core first formed shortly thereafter, transforming the geodynamo (the mechanism that creates the magnetic field) from a weak, unstable state into a strong, stable dipole field,” Driscoll said.
Tarduno said that the recovery of field strength after the Ediacaran earthquake with the increase in internal core likely played an important role in preventing the water-rich Earth from drying out.
As for the bizarre animals of the Ediacarans, they all disappeared by the following Cambrian period, when the diversity of life increased dramatically and the branches of the tree of life familiar today took shape in a relatively short time.
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