For more than a billion years after first emerging, life on Earth was stuck at the microscopic scale. Then, around 570 million years ago, small, simple bodies gave way to complex life: Scientists have discovered bizarre blob-like fossils, wriggling worm impressions, and strings of what were likely the poops of soft-bodied creatures from that period.
The trigger for this evolutionary leap has puzzled scientists for ages.
Now, new research published in Communications Earth and Environment points to a clue in Earth’s magnetic pulse. Scientists uncovered that the planet’s magnetic field was at a record low—around 30 times lower than today—for 26 million years starting around 565 million years ago. Such a drastic dip in magnetic field intensity could have had massive implications, according to the study’s authors.
“We think it may have played a role in possibly crossing a threshold of oxygenation and kick-starting the takeoff for [complex] animal life,” said study coauthor John Tarduno, a geophysicist at the University of Rochester in New York.
The strength of Earth’s magnetic field has fluctuated throughout its history. But realizing that this particular dip came perilously close to a collapse was “actually quite surprising,” he said.
Written in Minerals
Magmas encode the orientation and strength of their surrounding magnetic field as they cool and solidify. When the researchers first discovered a 565-million-year-old rock in Quebec, Canada, with a very weak magnetic signal, they were intrigued. They knew that the rock, made up of an amalgamation of minerals, had cooled slowly over nearly 75,000 years, however, so the measurement was therefore an average reading of the magnetic field strength over that time. The team needed better samples from more places to pin down a magnetic low.
The magnetic low lasted for at least 26 million years.
Collecting other rocks from that time in Brazil and South Africa, they looked for minerals such as feldspar and pyroxene, which encase very small needlelike magnetic minerals that form when magma cools. The team used scanning electron microscopes to precisely measure the ancient magnetic field direction and intensity recorded in those grains.
The magnetic low lasted for at least 26 million years. This partly coincided with a 10-million-year period of widespread oxygenation between about 575 million and 565 million years ago. The researchers suspected that Earth’s reduced magnetic field may have led to the rise in the oxygen level.
Earth’s Magnetic Pulse and Solar Wind
Earth’s magnetic field cocoons the planet, shielding it from the constant stream of charged particles emanating from the Sun that would otherwise erode the atmosphere. A rush of this “solar wind” struck the planet in May, causing widespread auroras and disrupting some communications systems.
“Imagine what would happen if such storms continued every day for at least 26 million years,” Tarduno posited. Such extreme solar forcing could have stripped light gas such as hydrogen from the atmosphere, according to the researchers. With Earth’s atmosphere rich in hydrogen- and oxygen-rich water molecules, this may have freed a lot of oxygen and led to a rise in oxygen levels.
“It wouldn’t be just a sudden jump.”
“It is an interesting idea—certainly something that needs to be out there and tested—but I don’t think it’s on firm ground yet,” said Joseph Meert, a paleogeographer at the University of Florida in Gainesville who was not involved in the study. His main concern was the accumulation of oxygen. He said that the process described would likely lead to a slow and gradual rise in atmospheric oxygen levels. “It wouldn’t be just a sudden jump.”
The hypothesis raises “some open questions,” said Manasvi Lingam, an astrobiologist at the Florida Institute of Technology in Melbourne who was not involved in the study. But “more modeling work is needed to rely on it.”
Simulations of interacting fluids could shed light, Lingam said. Researchers have used such tools to study atmospheric conditions on Mars and other planets. In this case, they might reveal how solar winds would interact with planetary atmospheres under an ultralow magnetic field.
—Saugat Bolakhe (@saugat_optimist), Science Writer