A new study suggests that as the magnetic field weakened, more sunlight reached the Earth, leading to an increase in oxygen that caused an explosion of multicellular organisms during the Ediacaran Period. The Ediacaran Period is a 96 million year geologic period that began at the end of the Cryogenian Period.
The Earth’s magnetic field sustains life on our planet, protecting us from solar winds, radiation and extreme temperature changes. But about 591 million years ago, it almost collapsed. As Smithsonian Magazine reports, this near-catastrophic event could actually be the key to an explosion of evolution that led to the development of larger and more diverse life forms.
The study, published in the journal Communications Earth & Environment, found that a severe weakening of Earth’s magnetic field lasting 26 million years corresponds to the Ediacaran period of the planet’s history. During this time, large amounts of oxygen in Earth’s atmosphere and oceans allowed the first multicellular, oxygen-using organisms to emerge from the sea.
The creatures that evolved during the Edicaran were unlike anything seen today; they took on disk-like forms, some of them over a meter in size. These include Earth’s oldest known animals, such as leaves, fans, drop-like Dickinsonia.
Scientists suggest that about 600 million years ago, without the protection of a magnetic field, solar radiation hit the Earth’s atmosphere, driving hydrogen and other light gases out of the atmosphere.
“If we’re right, this is a pretty profound event in evolution,” says lead author John Tarduno, a geophysicist at the University of Rochester.
The team examined rocks containing crystals that cooled over tens or hundreds of thousands of years based on studies of historical fluctuations in the magnetic field. These structures now act like time capsules, proving the strength of the magnetic field at various points in Earth’s development.
Analysis of feldspar from southern Brazil revealed that 591 million years ago the magnetic field was 30 times weaker than it is now. But two billion year old rocks found in South Africa show that the magnetic field then had the same strength as today.
Earth’s core was liquid, not solid. The liquid inner core churned as it released heat into the cooler mantle, moving molten iron around the core and enabling Earth’s magnetic field to exist. By the Ediacaran, this difference in temperature had decreased, reducing the movement of the core and, consequently, the presence of the magnetic field.
“By the Ediacaran period, the field was on its last legs and almost collapsed,” Tarduno said. “Then, as luck would have it, it cooled down enough and began to produce an inner core, strengthening the magnetic field.
The new findings also shed light on the long-standing question of at what point did the Earth’s core solidify? It also sheds light on the question. Previous estimates ranged from 2.5 billion to 500 million years ago, the new results place the event closer to 565 million years ago.
The solidification of the inner core was also a crucial event for the evolution of life. It allowed the Earth’s magnetic field to regain its strength and protected the planet’s water from being completely eroded by solar radiation.
“We need the Earth’s magnetic field to preserve water on the planet. But it’s interesting that the magnetic field, which was really weak during Ediacaran, helped accelerate evolution.” Tarduno said.
Geobiologist Shuhai Xiao, “Previously, the scientific consensus suggested that photosynthesizing organisms such as cyanobacteria created an excess of oxygen in the Ediacaran, which accumulated in the oceans over time. The new findings do not disprove this idea; on the contrary, they may show that the Earth gained oxygen in various ways.” said.
“We do not dispute that one or more of these processes occurred simultaneously. But the weak field may have helped the evolution of animal radiation by allowing oxygenation to cross a threshold,” Tarduno said.
Physicist David Dunlop said that while the latest studies need more work, the analyses are “flawlessly done”. “The hypothesis seems worthy of close scrutiny. It’s always difficult to prove causality, but I’m in favor of new ideas being put out for public scrutiny.”