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Earth’s Inner Core Is Older Than Expected by 500 Million Years

This finding promises to change our understanding of the Earth’s interior and its history. (Image: Pixabay/CC0 Public Domain)
This finding promises to change our understanding of the Earth’s interior and its history. (Image: Pixabay/CC0 Public Domain)

A new study of ancient rocks as they cool from magma has indicated that the Earth’s solid inner core may have started forming more than half a billion years earlier than previously thought.

Using new data, scientists from the University of Liverpool believe the Earth’s inner core was formed around 1-1.5 billion years ago as it “froze” from the surrounding molten iron outer core. As the core started to freeze, it began to generate a larger magnetic field, which it continues to do today.

Earth’s inner core is the innermost part of the planet, and scientists believed it is primarily a solid ball with a radius of about 760 miles (1220 km) — about 70 per cent of the Moon’s radius. It is primarily made up of an iron-nickel alloy with a temperature similar to our Sun of around 10,000°F (5,500°C).

Dr. Andy Biggin, lead author of the paper, said:

This finding could change our understanding of the Earth’s interior and its history.

The liquid iron freezes into a solid because it is under extremely high pressure. As the Earth cools, the inner core grows about 1 mm per year because of the freezing process. If scientists can work out when the iron first started to freeze, it would give them a reference point for the entire thermal history of the planet.

Biggin said: “The timing of the first appearance of solid iron, or ‘nucleation’ of the inner core, is highly controversial, but is crucial for determining the properties and history of the Earth’s interior, and has strong implications for how the Earth’s magnetic field — which acts as a shield against harmful radiation from the Sun, as well as a useful navigational aid — is generated.”

According to PHYS ORG, while 1 to 1.5 billion years is still relatively late in the Earth’s 4.5 billion year history, the Earth’s deep interior may not have been as hot in the deep past as some have argued.

Diagram of the Earth. (Image: Kelvinsong via wikimedia CC BY-SA 3.0)

A diagram of the Earth. (Image: Kelvinsong via wikimedia CC BY-SA 3.0)

“The theoretical model, which best fits our data, indicates that the core is losing heat more slowly than at any point in the last 4.5 billion years, and that this flow of energy should keep the Earth’s magnetic field going for another billion years or more,” Biggin wrote.

“This contrasts sharply with Mars, which had a strong magnetic field early in its history — which then appears to have died after half a billion years.”

That means the core is transferring heat to the surface more slowly than previously thought, and is less likely to play a big role in shaping the Earth’s surface through tectonic movements and volcanoes, PHYS ORG wrote.

Earth’s magnetic field is generated by the outer core; it does this by the turbulent action of the electrically conducting molten iron. The magnetic field is what protects Earth from the solar storms that the sun continuously throws toward the Earth.

The mystery of the Earth’s core is explained in the following video:

At the poles, these storms produce Aurora — northern or southern lights. But they can also work destructively to strip away ozone in the upper atmosphere, an important shield against the Sun’s harmful ultraviolet radiation, Nature World Report wrote.

Dr. Richard Harrison, from the University of Cambridge, who was not directly involved in the study, told The Standard Daily: “Studying the magnetism of ancient rocks is a huge scientific challenge, because old rocks can lose their magnetic memory, or the magnetic signals they carry can become overwritten and corrupted (just like the files on your hard drive).”

“However, it is one of the best ways to look for concrete evidence of when the core started to solidify. Although data are scarce, this study applied strict quality controls to decide which data were the most reliable — and then used statistics to demonstrate that a boost to the Earth’s magnetic field occurred 1,300 million years ago. If this turns out to be the elusive signature of inner core growth, then we may have to revise our ideas about the core yet again!” Dr. Harrison added.

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