We still don’t know how old Earth’s magnetic field is

Hyperaxion April 8, 2020 7:55 pm

MIT scientists analyzed a study on the subject based on zircon crystals published in early 2020. According to them, the method is not reliable.

In January this year, a team of scientists from the University of Rochester, in the United States, published a study arguing that the Earth’s magnetic field would have formed 4.2 billion years ago, 750 million years earlier than imagined. However, a new analysis by experts at the Massachusetts Institute of Technology (MIT) contradicts this theory.

We still don't know how old Earth's magnetic field is
MIT disputes the claim that the Earth’s magnetic field is 4.2 billion years old. The aurora borealis is a phenomenon that only exists because of the magnetic field. (Credit: NASA).

Both analyzes were based on zircon crystals found in Australia. This material is one of the oldest minerals we know and is scientifically important because it “stores” information about the magnetism of the region where it was formed. So, as scientists believe that Australian zircon was formed around the same time as Earth’s magnetic field, studying the material would be crucial to deduce how long the magnetic field has been around.

When MIT researchers, who have been investigating this scientific field since 2001, became aware of the article, they decided to take a closer look at the properties of Australian zircon. As they explain in their study, published on Wednesday (8) on Science Advances, the findings of other scientists are not enough to date the Earth’s magnetic field with such precision.

Methodology

To reach this conclusion, the scientists investigated about 250 zircon crystals formed over 3.5 billion years ago. The team isolated and photographed these samples, looking for signs of cracking or secondary materials, such as minerals that may have been deposited on or inside the crystal after it formed, or evidence of heating – the heat interferes with the magnetic properties of minerals of the type.

Of these 250, they identified only two zircons that were relatively free of impurities and contained a magnetic mineral called magnetite, used for measurements of the type. Analyzing these samples with the aid of microscopes, the researchers found that they had been damaged by contact with other substances.

Tiny zircon crystals found in Australia on a US dime.
Tiny zircon crystals found in Australia on a US dime. (Credit: University of Rochester / John Tarduno).

Taking all of this into account, MIT scientists concluded that zircons cannot be used as reliable records of the Earth’s magnetic field. “We showed that, before 3.5 billion years ago, we still have no idea when the Earth’s magnetic field started,” said Cauê Borlina, one of the researchers, in a statement to the press.

The team also made a point of stressing the importance of the work of their colleagues at the University of Rochester. “As a result of all the work from both groups, we now understand much better how to study the magnetism of ancient geological materials,” said Benjamin Weiss, co-author of the research. “We now can begin to apply this knowledge to other mineral grains and to grains from other planetary bodies.”

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