Science has published a paper by Smith et al, (Large gem diamonds from metallic liquid in Earth’s deep mantle) in which, inter alia, they note one inclusion containing methane,
They found that a few of the offcuts contained grains of majorite – a type of garnet found in Earth’s upper mantle, that only forms under very high pressures.
That wasn’t so surprising, we already know that diamonds require insane amounts of pressure to form, but then they found that other inclusions were made from a mixture of iron, nickel, carbon, and sulphur – a combination that’s never been seen in a ‘common’ diamond before.
They also found traces of methane and hydrogen that had formed around these inclusions like a shroud – something that had also never been observed in a diamond before.
“That’s unusual. This is the first time I’ve seen methane around an inclusion,” Smith told Rae Ellen Bichell NPR. (LH – My bolding)
Methane at depths of 750 kilometres below the Earth’s surface?
Abiotic oil anyone?
(Incidentally the gem quality stones described in the paper are restricted to kimberlites found on the stable cratons of the Earth’s crust).
Update: Depth estimates of melts are derived from modelling of Pressure (P) and Temperature (T) under the assumption of the process of self-gravitation. However an alternative mechanism could include P,T and E, the electric field strength, which could result in diamond and other high pressure mineral phases being stable at shallower depths than if only P&T were used.
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