The Cavendish experiment first determined the mass of the Earth and (arguably) the gravitational constant. However, given the ubiquitous nature of dark matter, it seems reasonable that at least some of Earth's total mass comes from dark matter accumulated at the center of the Earth.
If this is the case, Earth's calculated mass would include the masses of both 'light' matter and dark matter. The Cavendish experiment would be offset less by this, because most of the dark matter in the Earth would be near to its gravitational center (which is far from the site of the experiment). So G would be more well-estimated than the light mass of the Earth.
This would all be academic, if it weren't for the fact that models of the interior of the Earth assume that all matter is light matter (I presume).
We know the mass of individual electrons and protons to high precision from particle physics, as well as the larger mass of atoms from the interactions of the strong force; this knowledge can used to estimate what materials Earth contains given its density (from mass and size). But the true light density of the Earth could be significantly less than Earth's combined masses would suggest. It seems to me that we could be greatly overestimating the amount of light matter inside the earth, leading to an overly-dense geologic model of the Earth's core.
Is this possible? Is it likely? If not, why not?