EARTH
In the literature: contested
When did Earth's solid inner core begin to grow?
In plain words
Estimates of the inner core's age range from about half a billion to several billion years. The answer depends on how fast the core loses heat.
Precise statement
Determine the inner-core nucleation age $t_{ic}$. Thermal models give $t_{ic}$ of roughly 0.5 to 1.5 Gyr for high core conductivity and much older values for low conductivity; paleomagnetic candidates include the Ediacaran ultra-weak field near 565 Ma and a Mesoproterozoic intensity rise near 1.3 to 1.5 Ga. An answer is $t_{ic}$ with uncertainty below about 0.2 Gyr consistent with core energetics and the paleointensity record.
What would settle it
A resolved core conductivity and heat budget combined with a dense, reliable Precambrian paleointensity record showing a unique nucleation signature.
See also
- Related Which light elements make Earth's core less dense than iron?
- Related How did the inner core nucleate without implausible supercooling?
- Related Origin of strong magnetic fields in white dwarfs
- Related What powered the geodynamo before the inner core existed?
- Related Thermal conductivity of liquid iron alloy at core-mantle boundary conditions