Did a magnetic field collapse shape evolution?

The Earth’s magnetic field apparently has a complex significance for life on Earth. Petrovich9/iStock

A temporary weakening of the earth’s magnetic field may once have promoted evolutionary developments, a study shows: The researchers have found evidence of a near collapse of the earth’s umbrella between 591 and 565 million years ago, which may be linked to the flourishing of animal life in this era was. As they explain, the weak magnetic field may have contributed to the increased oxygen availability at the time, which benefited the organisms.

The earth’s magnetic field is considered one of the decisive factors that made life on our planet possible: like a kind of protective shield, it protects organisms from the sun’s aggressive particle radiation. In addition, the magnetic field prevented the solar winds from tearing the Earth’s atmosphere out into space. We owe this protective shield to a kind of dynamo system: flows of liquid iron around the solid inner core of the earth ensure the physical effect. However, it was not always equally strong: it is known that the process has been subject to fluctuations in the earth’s history, which have led to periods with earth’s magnetic fields of different strengths.

There were already indications that the field could have weakened during a special period in Earth’s history. This is the so-called Ediacaran period, which began 635 years ago and ended around 540 million years ago. What’s special: According to fossil finds, the first animal forms in the sea that can be seen with the naked eye developed during this era. Some representatives of this bizarre Ediacaran fauna even reached lengths of over one meter.

On the trail of the magnetic field in the Ediacarium

The characteristics of these creatures suggest that they required a lot of oxygen compared to previous life forms. Geochemical studies have already shown that the “elixir of life” was actually increasingly available in the water in the Ediacaran. However, it has so far remained unclear which factors contributed to the increase in oxygen. The international research team led by Wentao Huang from the University of Rochester now shows a possible connection between the change in the earth’s magnetic field, the increase in oxygen content and the evolutionary development boost in the Ediacaran.

Their study is based on a more precise characterization of the state of the magnetic field over the course of this era. The researchers analyzed material from a rock formation in Brazil that dates back to the Ediacaran period. The crystals of certain apatite minerals were in their sights. They contain magnetic particles in which information about the Earth’s magnetic field was preserved at the time of their creation, the scientists explain. Through investigations using modern analysis methods, she was now able to uncover the magnetization in the ancient rock and compare it with other data.

Magnetic field lull lasting 26 million years

As the team reports, analysis of the crystals revealed that Earth’s magnetic field at the time they were formed was the weakest ever measured. The field strength was therefore around 30 times lower than today. According to the researchers, the results, combined with information from previous studies, suggest that the extremely weak level spanned the period from 591 to 565 million years ago. The researchers point out that this overlaps strikingly with the known high oxygen content in the atmosphere and in the sea, which is evident from 575 to 565 million years ago.

But how could the weak magnetic field have led to more oxygen? The researchers provide a plausible explanation for this in their study: The weak magnetic field made it easier for the sun’s charged particles to drive the light hydrogen atoms from the atmosphere into space. There would have been less reaction material in the atmosphere for the formation of water from oxygen and hydrogen. Over time, oxygen could have accumulated and eventually found its way into the ocean water, the researchers explain.

According to them, this effect could have contributed to the strong development of early animal life in the Ediacaran. These organisms then formed the evolutionary basis for the further development of life in the following Cambrian era. During this time, the newly strengthened magnetic field then resumed its long-term role as a protective shield for life: “If the extremely weak field had persisted after the Ediacaran, the Earth could look completely different today: the loss of water might have caused our planet to gradually dry out.” says co-author John Tarduno from the University of Rochester. “I find the idea that processes in the Earth’s core could ultimately be linked to evolution fascinating,” the researcher concluded.

Source: University of Rochester, specialist article: Communications Earth & Environment, doi: 10.1038/s43247-024-01360-4

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