Deeply flawed diamonds

A report in September's Geotimes suggests that...

"Diamonds with garnet inclusions containing a mineral called majorite can form at depths up to 500 kilometers below the surface, and scientists now say that the diamonds may have an organic source from the surface of Earth."
It goes on to say that...

"some rare diamonds have been found with garnet inclusions containing a silica-rich mineral called majorite that only forms below 250 kilometers. Majoritic garnets, acting as depth gauges, revealed that some diamonds can form at depths up to 500 kilometers. But how the carbon got to such depths remained unknown."

Well, it seems to me that the a priori assumption is that the carbon came from the surface through the typical means of today's geology. However, for all those who have read the debate concerning the abiotic theory of hydrocarbons there is an alternative that suggests there is plenty of carbon down there already. That doesn't mean that the carbon didn't come from the surface, as life may extend that deep for all anyone really knows. The oil we pump to the surface may be a result of the action of bacteria and nanobacteria living in the crust.On the other hand, orthodox theory may be right, and if it is, life on Earth may have suffered much more greatly from catastrophic events than previously thought.