Today, Earth’s magnetic field acts as a safety blanket, shielding the planet from dangerous solar wind. Without the protection of our magnetosphere, you, me and almost every other living thing on Earth would not fare very well being pummeled by streams of harmful particles from the sun.
A reduction in Earth’s magnetic strength during a period that spanned at least 591 million and 565 million years ago coincided with a spike in oxygen levels and a boom in biodiversity, according to a study published Thursday in the journal Communications Earth & Environment.
The reason, the researchers say, is that a torrent of solar radiation that pelted Earth’s atmosphere when the magnetic field weakened knocked away hydrogen and other lightweight atoms, leaving an overabundance of oxygen in its wake. That oxygen, in turn, fueled the growth of bigger, oxygen-breathing multicellular organisms.
The wave of evolution just as the magnetic field weakened is “so striking that we felt this could not just be a coincidence,” said John Tarduno, a geophysicist at the University of Rochester who helped conduct the research. “It’s a surprising result.”
The idea will need further testing to gain wide acceptance. “The hypothesis, although obviously speculative as any ideas about the earliest origins of life must be, seems worth a close look,” said David Dunlop, a professor emeritus at the University of Toronto who was not involved in the research.
Many of the organisms at this time — called the Ediacaran Period — would look alien to us today. Some were shaped like ribbed disks, others like clumps of plantlike fronds. Well before the age of dinosaurs, these things ruled Earth. Though scientists still debate where exactly to place them on the tree of life, the organisms of this era may be some of the first multicellular animals on Earth.
After digging up initial evidence that something strange was going on with Earth’s magnetic field hundreds of millions of years ago, Tarduno’s team wanted more rocks in which Earth’s magnetism left an impression. “We were searching around the globe for the right rock types,” he said.
They found their answer in feldspar in the rolling hills of Brazil, which formed from slowly cooled magma deep in Earth’s crust. Their analysis revealed that the intensity of Earth’s magnetic field was 30 times weaker than today’s, at a time when the rock and fossil record tells us oxygen levels were rising and life forms were proliferating.
“Causality is always hard to prove, but I am all for new ideas being put out for public scrutiny,” Dunlop said. “It provokes further study and that is all to the good.” He added that the magnetic analysis of the rock was “impeccably done.”
Manasvi Lingam, an assistant professor at the Florida Institute of Technology who was not involved in the study, said the research “offers support for the hypothesis” that a weak magnetic field and the diversification of life are linked — an idea, he said, that has bounced around since the 1950s. But he added that more research is needed, including work simulating just how much hydrogen would actually escape.
Earth’s magnetic field eventually recovered in strength after the planet’s inner core froze solid, Tarduno said, following several million years of the magnetic field being in a weakened state. We’re lucky that happened. Had Earth’s atmosphere been left naked to solar wind for much longer, the planet could have dried out and looked much different than it does now.
“The shields couldn’t be down for too long,” Tarduno said. If they were weak for much longer, “we would have lost a lot more water on Earth, and we would have probably had a very different evolutionary path.”
