Earth’s inner core is 1 billion years old

Hyperaxion September 1, 2020 12:43 am

Scientists were able to calculate the age of the Earth’s inner core with greater accuracy than previous studies.

By creating conditions similar to those at the center of the Earth inside a laboratory chamber, Chinese and American researchers refined the estimate of the age of our planet’s solid inner core.

Earth’s inner core is 1 billion years old
(Credit: Kelvinsong – Own work, CC BY-SA 3.0).

The study, published in early August in the journal Physical Review Letters, suggests that the planet’s core was formed between 1 billion and 1.3 billion years ago, contrary to theories that claim that this occurred between 1.3 billion and 4.5 billion years or, as a more recent hypothesis suggests, 565 million years ago.

Knowing the age of Earth’s core is important to understand how the matter at the center of the planet conducts heat and how the mechanisms that support the Earth’s magnetic field work.

“People are really curious and excited about knowing about the origin of the geodynamo, the strength of the magnetic field, because they all contribute to a planet’s habitability,” explained Jung-Fu Lin, one of the scientists responsible for the study.

The Earth’s core is mainly made of iron, with a solid inner part and a liquid outer part. According to experts, the effectiveness of iron in transferring heat through conduction is the key to determining several properties of the core, including when its inner part was formed.

Over the years, age and conductivity estimates have varied widely, from very old and relatively low, to very young and high. This created a paradox.

As the scientists explain, these theories suggest that the planet’s core would have to reach extremely high temperatures, maintaining the geodynamo for billions of years before the formation of its solid part.

Computer simulation of the Earth's magnetic field, which is generated by heat transfer in the core.
Computer simulation of the Earth’s magnetic field, which is generated by heat transfer in the core. (Credit: NASA / Gary A. Glatzmaier).

The new research solves this paradox by finding a solution that keeps the core temperature within more realistic parameters.

In the new article, the team suggests that the recently measured conductivity is 30% to 50% less than previously estimated, suggesting that the geodynamo was maintained by two different energy mechanisms: thermal convection and compositional convection.

To reach this conclusion, the team measured iron conductivity in conditions similar to those of the planet’s core, where the pressure is greater than 1 million atmospheres (atm) and temperatures are as high as on the Sun’s surface.

Emulating these conditions was no easy task, but after two years researchers achieved them by compressing laser-heated iron samples between two diamond anvils.

The hard work paid off, as scientists learned more about iron conductivity and heat transfer over time, and were able to make a more accurate estimate of the age of Earth’s inner core.

“Once you actually know how much of that heat flux from the outer core to the lower mantle, you can actually think about when did the Earth cool sufficiently to the point that the inner core starts to crystalize,” Lin said.

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