The force that keeps shopping lists stuck to your fridge could help explain why there’s more than one cell in your body, according to new research.

Earth is a giant magnet, and the atmosphere stays in place because of this magnetism. But the atmosphere wasn’t always as thick as it is today, nor was the magnetic field as strong. Scientists think that about 500 million years ago, Earth’s core solidified, turbocharging our magnetic field. This would have allowed the atmosphere to hold more gas, in part shielding early life from powerful solar rays – and allowing multicellular life to evolve.

“The origin of life remains one of most challenging themes in science,” the study's authors note. But they think they have an answer, at least when it comes to the evolution of multicellular life. The team from NASA and Sapenzia University in Rome recently published its research online in Geoscience Frontiers.

For 3 billion years, life on Earth was only home to water-dwelling, single-celled organisms like bacteria. But suddenly, multicellular life ballooned, knocking over the first domino in an evolutionary cascade that would one day allow you — yes, you — to exist and think and even read stuff on the Internet.

Scientists think that until 500 million years ago, life on Earth fell victim to high-energy blasts from the sun, which at the time contained a lot more of the cell-killing gamma, ultraviolet and x-rays than it does today. The atmosphere then was too thin to fully protect our single-celled ancestors, whose DNA would have been damaged by such powerful rays. That kept them from becoming more complex.

But every bacterium must have its day.

As Earth got older, heavier metals like iron and nickel sunk to the center and solidified under the pressure of the rest of the planet. Once the inner core was solid, it started spinning separately from the outer core. That would have made Earth into a more powerful magnet, which could have boosted its magnetic field.

Scientists think the stronger magnetic field would have kept more gasses in the atmosphere, just as a stronger magnet can hold more paper clips. That means more oxygen was around to help cells grow, and a thicker atmosphere could protect those budding organisms from solar blasts. Simultaneously, the aging sun’s radiation started weakening, which means its flares contained fewer dangerous, DNA-altering rays.

That perfect confluence allowed the number of species to skyrocket, the authors say.

Others also emphasize the importance of Earth’s magnetic field as crucial to life on the planet. Recent work even suggests Mars's lack of strong magnetic field was what allowed the sun to strip away its atmosphere, leaving the planet barren.

You “have to have a magnetic field, because that protects the atmosphere from erosion and the complete removal of water,” John Tarduno of the University of Rochester told Wired in 2010. His group estimated Earth’s magnetic field as about 3.5 billion years old.

The authors of the most recent study caution that it’s difficult to peg exactly when life began, or when the inner core of the planet solidified, which makes it difficult to link the two events for certain.

Regardless, they think some major changes must have gone down that allowed life to flourish here. A sudden leap in the power of the magnetic field could have been the jump-start the world needed.

Ryan Mandelbaum is serious about science, pizza, Guy Fieri and not much else. He enjoys writing about the environment, physics and the macabre.

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