The problem with your metaphor is that the beads are inanimate and there is no "filter" in reality. There is no sorting hat that makes people pick careers. As Hollywood inadvertently made clear to the general public, even in the 60s, with Jim Crow still a thing, black women could get exemplary mathematics educations and jobs in the field. There might have been colossal barriers in their way, but some people could surmount them.

But there are also cultural issues that influence people's choices and mean that different groups are going to think of different things.

Here's a possibility. CRT and other such woke instructional efforts spur black students toward success-coded fields to prove they can or get a win for the team, or else toward racial awareness sorts of things like black studies and sociology and history and other fields that might pertain toward racial consciousness. When "being black" is a major thing that academia is constantly making black people take an interest in, that skims off a lot of people from the sorts of knowledge-for-knowledge sake course of study that lead people into geology.

How many people dream of being geologists, after all? I'd guess most people sort of stumble into it, because they get involved with something akin and like it, follow up and then pursue it for a career.

You're working from a faulty premise - that society is a demographic fractal, which is utterly unproven. That the demographics of any given aspect should identically reflect the population. And there is no proof that this is or should be the cause absent racism or other forms of discrimination. A study was done, and NO national military force represents the demographics of its state. And there are no patterns. Sometimes minority groups are overrepresented and sometimes they are underrepresented (contrary to Hollywood's depictions, Hispanics are actually underrepresented in the US armed forces in general, but Hispanic women are overrepresented). Sometimes the minorities are privileged or discriminated against, and there is no consistent correlation with their representation in the military. Even in countries where there is conscription we can't predict the demographics by extrapolating from the population.

To the extent that systemic discrimination is racist, it's no more of a problem than the distribution of sunburn or sickle-cell anemia or diabetes. If you're white, you're going to have an uphill battle breaking into the NBA, if you're Hispanic or Oriental, same problem with the NFL. If you're black, you're going to have a few more barriers to getting into geology, even if those are nothing more than a lack of any acquaintances or mentors (for instance, if blacks are constantly told white people see them differently and won't give them a break or will judge them by a different scale, they are going to be more inclined to seek black mentors, thus closing off whole fields of study or work in which blacks are already underrepresented) who might introduce you to the field.