Earth’s inner core plays a vital role in generating the magnetic field which protects our planet from harmful solar wind—streams of radiation coming from the sun—and makes the Earth habitable. However, scientists had numerous speculations and studies about the age of this inner core.
A recent study conducted by researchers in the University of Rochester indicated that the Earth’s inner core is younger than what scientists thought, offering a new insight into the history of the Earth’s magnetic field and planetary habitability.
The study published by Nature Geosciences on Monday said that the inner core started to solidify only about 565m years ago—relatively younger than our 4.5bn-year-old planet.
“Until this data, the age of the inner core was uncertain,” said John Tarduno, a professor of earth and environmental sciences at Rochester. Tarduno informed Daily News Egypt via email, “There is this huge range of 2bn years, which scientists think is the time frame when the inner core was formed. These are the first field-strength data from the younger part of the range of possibilities suggesting that the inner core is really young.”
Earth’s magnetic field is generated in its liquid iron core via geodynamo—a process during which the kinetic energy of conducting moving fluids is converted into magnetic energy. Researchers believe a weak geodynamo—and a magnetic shield—formed early in Earth’s history, shortly after the event which created the Earth’s moon.
For the next several billion years, the energy to drive the dynamo decreased until a critical point 565m years ago, when “the dynamo was on the point of collapse,” Tarduno said. Despite its drastically weakened state, however, the dynamo did not go away. The researchers conjectured it was at this point in the geological time scale—or sometime shortly after—that the inner core began to form, giving strength to the geodynamo.
“This is a critical point in the evolution of the planet. The field did not collapse because the inner core started to grow and provided a new energy source for the formation of the geodynamo,” Tarduno said.
To know about the evolution of the geodynamo, the researchers of the study measured the strength of the ancient magnetic field locked within single crystals of the mineral feldspar. The samples were collected from the Sept-lles Complex in northern Quebec and contain tiny magnetic needles with ideal recording properties.
“The feldspar protects those needles from later alteration on geological time scales, so we get a much higher resolution record of the ancient strains in the magnetic field by measuring these single crystals,” according to Tarduno.
By studying the magnetism locked in ancient crystals—a field known as palaeomagnetism—the researchers found that the intensity of the magnetic field was extremely low 565m years ago, lower than anything we have ever seen before. This indicates that the inner core may have formed around this time in order to restore strength to the dynamo and, in turn, to the magnetic field.
Our magnetic field is part of what makes Earth a special planet, and, so far, the only one that has life. The evolution of the Earth’s interior and the resulting geodynamo generated within play a critical role in the preservation of life, according to the research.
An improved understanding of this evolution of the Earth’s interior may provide researchers key clues, not only for planet formation and habitability on Earth, but in the search for life on exoplanets which resemble Earth.
“The same factors which drive dynamos on Earth might affect the magnetic shielding on exoplanets. It could be the case that some planets do not have long-lived dynamos and those planets would not have the magnetic shielding we have, meaning that their atmosphere and water might be removed,” Tarduno said.
Besides being a critical point in the evolution of Earth, almost 565m years ago was also a critical time for the major diversification of life on Earth. This is a time of Ediacaran fauna, the first large complex organisms we saw in the geologic record. These are a fundamental change from the microbial life preserved in older rocks.
“It is true that if we have lower magnetic shielding, we would have more harmful radiation coming in to the Earth. That radiation might be harmful for DNA, for example, and there has been speculation that this could stimulate mutations,” Tarduno said. Although, there isn’t a strong evidence of this correlation in the geological record, the new data will certainly stimulate more thoughts on this issue.