Inner core

Earth’s field almost died. A young inner core is one reading.

Living Earth

Earth’s field almost died. A young inner core is one reading.

Crystals from the Sept-Îles intrusion in Quebec record a magnetic field about ten times weaker than today’s, dated near 565 million years. That is the lowest time-averaged dipole yet pulled from extant rock. Directions from the same interval look messy: high scatter, frequent reversals. A field that weak, that unstable, is what some dynamo models predict just before a solid inner core begins to freeze.

Thirty-odd million years later the field is back. Early Cambrian anorthosites from Oklahoma, about 532 million years old, record a dipole several times stronger than that Ediacaran floor. One reading puts inner-core nucleation in the gap — near 550 million years. That number sits at the open of living Earth on this site.

This site reads Io through Mars as consecutive stages of one kind of planet, with living Earth as the present chapter. The quiet interval is the measurement. A young inner core is one reading of the gap. The record does not prove the handoff.

Figure 1. Time-averaged dipole moment, in 10²² A m². Today is about 8. Sept-Îles, ~565 Ma, is about 0.7 (Bono et al. 2019). The Oklahoma recovery, ~532 Ma, is about five times that Ediacaran floor (Zhou et al. 2022).

The ordinary view

A growing inner core changes how the dynamo is powered. Latent heat and light elements rejected into the outer core add a compositional kick that a purely cooling, still-liquid core does not have. If conductivity in liquid iron is high, that kick arrives late — a few hundred million years ago, not two billion. If conductivity is modest, the inner core can be older, and a field-strength step near 1 to 1.5 billion years is read that way instead.

The young age is therefore a package: ultralow Ediacaran intensity, a rapid Cambrian recovery, and high core conductivity. Take any one piece away and the date moves. Supercooling — liquid iron that must drop below its melting point before it can freeze — can move it again. This is not a closed case.

Which clock is which

Table 1. Two published nucleation camps, one measured quiet interval, and this site’s window.
Clock	What it is	What it is not
Quiet field ~565 Ma	Sept-Îles dipole ~10× weaker than today	Proof the inner core froze that year
Recovery ~532 Ma	Oklahoma rocks record a stronger dipole	A closed nucleation date
Young-core camp ~550 Ma	One reading of the gap, plus high conductivity	The only published age
Older-core camp ~1–1.5 Ga	A field-strength step read with modest conductivity	A second quiet interval at 565 Ma
Living Earth open ~567 Ma	A modeling window on this site	A crystallization law

What would move a clock

Table 2. The quiet interval can survive without a young inner core. The pairing with living Earth cannot survive if nucleation is locked a billion years earlier.
Row	What would move it	What would not
Quiet interval	Sept-Îles intensity shown to be ordinary, not ultralow	A few million years of new dating inside 565–532
Young nucleation	High conductivity withdrawn; older camp required	Supercooling moving the freeze by tens of Myr
Living-Earth pairing	Nucleation locked before 1.0 Ga with no Ediacaran floor	The same quiet interval kept as a measurement

On this reading

This site reads living Earth as the present chapter of a cycle whose equal windows are about 567 million years. The Ediacaran–Cambrian pair sits at the open of that chapter. A young inner core in the same bin of time would be a new power source arriving as the lid is already continental and the fossil record is already turning over. That is compatibility. It is not a crystallization law.

What would weaken this

A demonstration that the Sept-Îles field was ordinary would take the quiet interval off the table. A nucleation age locked before one billion years, with no Ediacaran floor, would take the living-Earth pairing off the table. Neither result would prove a handoff.

What this page holds

Earth’s field almost died near 565 million years. It recovered by about 532. A young inner core is one reading of that gap. This site reads the gap against the open of living Earth. The record does not prove the handoff.

Sources

Bono, R. K., and colleagues (2019). Sept-Îles ultralow dipole near 565 Ma.

Zhou, Y., and colleagues (2022). Early Cambrian recovery recorded in Oklahoma anorthosites, ~532 Ma.

Young inner-core camp tied to high thermal conductivity of liquid iron; older camp to a 1–1.5 Ga intensity step.

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