Geoscience attracts few African American and Hispanic/Latino students to the major and has historically not retained women at the same rate as men. Many factors have been proposed to explain these disparities but no quantitative study addressed geoscience diversity at the undergraduate level. To examine potential barriers to recruitment and retention, we interviewed geoscience majors from two large public universities in the U.S. and gathered 'critical incidents,' or life experiences that affected choice of a geoscience major. Critical incidents were classified by time period (when they occurred), grouped by outcome, sorted into categories, and compared by race/ethnicity and gender. Three manuscripts -- each involving different analyses of the critical incident dataset -- comprise this dissertation. Among many findings, our study showed that that white, Hispanic/Latino, and African American students reported different types of experiences affecting major choice while growing up. For instance, 81% of white students reported outdoor experiences (e.g., camping, hiking) as children, whereas Hispanics (33%) and African Americans (22%) reported significantly fewer outdoor experiences from the same time period. Men and women geoscience majors also reported differences. In one example, men (92%) reported at least one positive experience involving career and economics factors; far fewer women (50%) reported the same. Our results can inform recruiting and retention practices. Geoscience programs can provide field trips for all prospective majors, target on-campus advertising towards diverse student groups, meet with academic advisors of incoming freshmen to encourage African American and Hispanic students to enroll in introductory geology courses, and provide major and career information to parents of prospective majors. To better recruit and retain women, geoscience programs can emphasize other, non-economic factors when advertising the degree, promoting internships, and developing field and academic experiences.