Temporary weakening of magnetic shielding, new research suggests can create favorable conditions for the development of early life by increasing oxygen levels. “When the macroscopic animals of the Ediacaran fauna diversified and evolved, the Earth’s magnetic field was in a highly unusual state,” Wentao Huang of the University of Rochester and colleagues write in their new paper.

explosion of life

Scientists who examined magnetic signatures in rocks in Canada in 2019 reported that the samples showed: Earth’s magnetic field has weakened to lowest known level approximately 565 million years ago, during the Ediacaran period, when multicellular life was taking shape.

For a long time, it was thought that the small vanishing magnetic field would be harmful to emerging life because it shielded the solar wind. But not everyone agreed with this view of disaster. In 1965, planetary scientist Carl Sagan claimed: Earth’s atmosphere and oceans could have served as a protective shield for early life formsEven if the planet’s magnetic field is weak. This was confirmed by modeling in 2019.

But any connection between the coincidence of the weakening of the magnetic field, the explosion of Ediacaran life, and rising oxygen levels remains “tempting but unclear,” as Huang and colleagues put it.

So scientists began to investigate. They excavated igneous rocks in South Africa that formed billions of years ago and examined the crystals within them, as well as other 591-million-year-old rocks previously sampled from Brazil. These crystals contain tiny magnetic minerals that preserve the trace of the Earth’s magnetic field as it was when these crystals formed.

Combining their findings with those of a 2019 Canadian study, Wentao Huang and colleagues concluded that this weak magnetic field (called ultra-low time-averaged field intensity, or UL-TAFI) persists. at least 26 million years ago, 591 to 565 million years ago.

Coincidentally, this interval coincides with the increase in oxygen levels in the atmosphere and ocean during the Late Ediacaran period, approximately 575-565 million years ago, when a biodiversity explosion also occurred.

What is the connection?

But the question remained: How could an ultra-weak magnetic field lead to increased oxygen levels?. By modeling the evolution of the solar wind, Huang and colleagues suggest that the weakened magnetic field may allow more hydrogen ions to “escape” from Earth’s atmosphere into space, leading to higher oxygen levels in the seas and skies. It contributed to the explosion of life in the Ediacaran.

When we talk about such explosions, we usually think of the Cambrian explosion of life, which is considered the largest evolutionary explosion that gave rise to the complex life that evolved into the animals and insects we see today. But the Ediacaran period can also be a surprise. It is known for its slimy creatures that resemble primitive sponges, slugs and sea anemones. This was a period of great evolutionary experiments that led to many dead ends, and a sharp decline in biodiversity before life revived in the Cambrian.

Recent research suggests that the first complex ecosystems may have formed in the Ediacaran, and a 2022 study identifies increasingly complex community structures in Late Ediacaran fossils. Life needs oxygen to grow and become complex. Microscopic marine animals and sponges can survive in low-oxygen oceans, but larger, mobile animals with complex body structures require more oxygen to maintain their metabolism.

A complex animal ecosystem with long food chains and predators requires even more oxygen, as evidenced by the exclusion of such complex ecosystems from the modern oxygen minimum zone.
– explains Huang.

Although many of these creatures were doomed to reach an evolutionary dead end, Ediacaran life appears to have taken advantage of the moment when the Earth’s magnetic field weakened.