How much of Earth is carbon-based?
0.07% of the mass of the Earth is estimated to correspond to carbon atoms (computed from data on Abundance of the chemical elements that comes originally from this paper)

The following table is from the above link and show the relative abundances on Earth in parts per million of mass:


The original table in the source paper (which correspond to Chapter 1 in, EARTHQUAKE THERMODYNAMICS AND PHASE TRANSFORMATIONS IN THE EARTH'S INTERIOR) is this one: