Approximately 4.5-billion-years ago, Earth’s liquid iron core cooled enough to create a solid ball in the center. Now, our planet’s core comprises a solid iron inner core enclosed by a molten iron outer core.
Telling exactly when this change happened has proven quite challenging. Evaluations range from 4.5 billion years ago to 565 million years ago. But, thanks to a new study, the age of Earth’s inner core has been finally narrowed down. Here is what you need to know.
The Age of Earth’s Inner Core Revealed: Features and Significant Details
According to data obtained in lab experiments that model conditions similar to those in the planetary core, Earth’s inner core is between 1 billion and 1.3 billion years. Such a result helps scientists determine the age of geodynamo, which feeds the magnetic field around our planet. The geodynamo is produced by the flow of conducting iron in the outer core, influenced by convection that’s fueled by two mechanisms.
For the new study, scientists looked into the thermal conductivity of iron under pressures and temperatures approaching those in the core. And to do such a thing, they took an iron sample, heated it with lasers, and squished it in a diamond anvil. After many attempts, they succeeded in measuring the thermal and electrical conductivity of the sample under 170 gigapascals of pressure and 3,000 Kelvin temperatures.
When the scientists measured the conductivity in the sample, they discovered it to be 30 to 50 % lower than what would be needed for the 565-million year age estimate for Earth’s inner core. Hence, they could set a top limit on the thermal conductivity of liquid iron under core conditions.
Jung-Fu Lin, a geoscientist at the University of Texas in Austin, explained that: “Once you actually know how much of that heat flux from the outer core to the lower mantle,” things become easier to understand. Also, the scientists succeeded in finding out when the Earth cooled sufficiently to the point that the inner started to crystallize.
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