"It's a natural question to ask where did this carbon that we are all made of come from and how much carbon was originally supplied when the Earth formed," Mookherjee said. "Where is the bulk of the carbon residing now? How has it been residing and how has it transferred between different reservoirs? Understanding the total inventory of carbon is what this study gives us insight to."
The carbon abundance of Earth has been an issue in the solar nebula and accretion disk modeling. Example, Follow the Carbon, Sky & Telescope 140(6):34-40, 2020 An interesting report on carbon in Earth and how the accretion disk model for the solar system has some real problems here. Earth's ratio of carbon to silicate is 0.001 where it should be 4, a factor off by 4000.
Carbon-grain sublimation: a new top-down component to protostellar chemistry, https://ui.adsabs.harvard.edu/abs/2020EPSC...14..960V/abstract
, "One of the main goals in the fields of exoplanets and planet formation is to determine the composition of terrestrial, potentially habitable, planets and to link this to the composition of protoplanetary disks. A longstanding puzzle in this regard is the Earth's severe carbon deficit; Earth is 2-4 orders of magnitude depleted in carbon compared to interstellar grains and comets. The solution to this conundrum is that carbon must have been returned to the gas phase in the inner protosolar nebula, such that it could not get accreted onto the forming bodies..."
My observation. Explaining the origin of carbon on Earth and its abundance and balance using the solar nebula and accretion disk model is not easy. Earth could have too much carbon and end up looking like Venus.