Figure 13.

Mn-Cr isochron diagram for dolomite grains. By assuming a homogeneous distribution of the (⁵³Mn/⁵⁵Mn)₀ in the early solar system, the ⁵³Mn-⁵³Cr age of dolomites, was calculated by the (⁵³Mn/⁵⁵Mn)₀ = 4.14 × 10⁻⁶ relative to the D’Orbigny angrite with (⁵³Mn/⁵⁵Mn)₀^D’Orbigny = (3.24 ± 0.04) × 10^{−6 36)} and the decay constant of ⁵³Mn.³⁷⁾ The absolute age of dolomite grains was estimated to be ${4564.7}_{-1.0}^{+0.8}$ Ma by referring to the Pb-Pb age of the D’Orbigny angrite with t^D’Orbigny = 4563.37 ± 0.25 Ma.^38,39)