30 times weaker magnetosphere may have helped life thrive

Complex life on Earth may have emerged more than 541 million years ago due to strange fluctuations in the planet’s unique magnetic field.

Unlike its 3 closest rocky planets, Earth produces a magnetosphere thanks to convective interactions in the planet’s iron core layers. This generates huge electrical currents that extend beyond the crust and form a ‘shield’ to protect against harmful solar radiation from the Sun.

In many ways, this field helps life on the surface thrive, redistributing charged particles thrown towards the Earth from the Sun and deep space.

But a brief collapse of this field may have enabled the development of the most complex lifeforms on the planet during the Ediacaran Period, according to a study led by University of Rochester (US) researchers.

Records show that soft-bodied animals underwent a surge in diversification 575-565 million years ago and likely due to increased oxygen in the atmosphere and ocean.

A dip in the strength of Earth’s magnetic field 591-565 million years ago happened alongside the oxygen spike.

The Rochester team led by earth scientist John Tarduno proposes this change – described as being “the weakest time-averaged value in the magnetosphere,” – about 30 times weaker than the field strength today – contributed to the rise in oxygen levels.

“Previous ideas for the appearance of the spectacular Ediacaran fauna have included genetic or ecologic driving factors, but the close timing with the ultra-low geomagnetic field motivated us to revisit environmental issues, and, in particular, atmospheric and ocean oxygenation,” says Tarduno.

Their proposal stems from an analysis of magnetism of 591-million-year-old feldspar and pyroxene crystals from anorthosite rocks. These minerals ‘lock in’ the strength of the Earth’s magnetic field when they form and makes them effective records of the state of the magnetosphere.

The analysis indicates the massively weakened magnetic field persisted for around 26 million years. Tarduno’s team suggests the rise in the percentage of oxygen may have been caused by the escape of atmospheric hydrogen through the Earth’s weakened shield.

Luckily the return to strength during the Cambrian Period – which saw the mass emergence of fossil record animals – enabled life to thrive, as opposed to a Mars-like situation where prolonged magnetic field weakening could have seen water slowly disappear from the planet.

“If the extraordinarily weak field had remained after the Ediacaran, Earth might look very different from the water-rich planet it is today: water loss might have gradually dried Earth,” says Tarduno.

The study is published in the journal Communications Earth & Environment.

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