Scientists reduce the age of the Earth’s inner core


At some point in Earth’s 4.5-billion-year history, its completely liquid iron core cooled enough to form a solid ball in the center. Today, our planet’s core consists of a solid iron inner core, surrounded by an outer core of molten iron, but when this change has occurred it proves to be absolutely difficult.

Estimates range from 4.5 billion years ago – the age of the Earth – to 565 million years ago; Now, a new study has finally narrowed it down. According to data obtained in laboratory experiments that create positions reaching them in the planetary core, the age of the inner core must be somewhere between 1 billion and 1.3 billion years.

In turn, this helps us to reduce the age of geodynamo, which powers the magnetic field around the Earth. This magnetic field contributes to life in hospitable conditions as we know it protects the planet’s atmosphere from being blown up by solar wind.

Therefore, it would be no surprise that scientists have a keen interest in how it came into existence, and how it is maintained.

“People are really curious and excited about learning about the strength of the magnetic field, because they all contribute to the planet’s habit,” said Jung-Fu Lin, a geologist at the University of Texas at Austin.

Geodynamo is formed by the circulation of iron conduction in the outer core, driven by convection that is driven by two mechanisms.

First, there is thermal convection resulting from temperature fluctuations; It can occur entirely in the liquid core. Secondly, there is convection structure, in which liquid elements rise in the inner core boundary through the liquid outer core, creating momentum.

In both cases, this conductor creates liquid electric currents that basically charge, essentially transforming it into a giant electromagnet. At voila! A magnetic field. Currently, both types of convection exist in the Earth’s core, contributing equally to geodynamo.

But before the solid core crystallized, only thermal convection was possible in the Earth’s core. It is capable of generating geodynamo, but to maintain it for billions of years, as is required for small estimates of the age of the inner core, iron needs to be overheated – improperly.

In order to operate and maintain such temperatures, the thermal conductivity of iron – as such, the ability to conduct heat efficiently – needs to be high. Therefore, the team decided to look at the thermal conductivity of iron under pressure and at temperatures approaching the core.

To do this, they took an iron sample, blasted it with lasers to heat it and squeezed it into a diamond anvil. It took longer than it takes to describe: several attempts over two years. In the end, however, the team managed to measure the electrical and thermal conductivity of the sample under a pressure of 170 gigaspascals (which is 170 million times the atmospheric pressure at sea level), and temperatures of 3,000 Kelvin.

The pressure in the outer core ranges from the outer limit to the inner limit range from 135 to 330 gigapascals, while temperatures range from 4,000 to 5,000 Kelvin. The inner core is believed to reach above 6,000 Kelvin (but iron freezes under intense pressure).

When the team measured the conductivity in the sample, they found it to be 30 to 50 percent lower than required for the 565-million-year age estimate for the inner core. Therefore, researchers can place an upper limit on the thermal conductivity of liquid iron under the main conditions – which, in turn, puts a higher limit on how much heat can be handled and maintained.

With all of this, they can finally estimate the age of the Earth’s inner core.

“Once you really know how much heat flows from the outer core to the lower ventilator, you can actually think about how the Earth cooled down enough to the point that the inner core starts to crystallize , “Lynn said.

The team’s timing, interestingly, falls neatly with changes in the Earth’s magnetic field. The arrangement of magnetic materials in rocks from 1 to 1.5 billion years ago suggests that the magnetic field strength increased during this time – as would be expected for the time when the inner core crystallized.

However, a similar increase was also seen 565 million years ago. If the inner core first crystallized, it means that everything Earth did 565 million years ago is still a mystery.

Researchers wrote, “Resolving this discrepancy requires further inquiry between mineral physics, geology and paleontology.”

The research has been published in Physical review letter.

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