地球化学是对地球及其组成部分（包括大气层，水圈，地壳，地幔和核心）以及地外物质（如陨石和彗星，其他行星，太阳，和遥远的星星。它涉及地球及其大气中元素的分布和迁移。随着时间的流逝，地球化学已经从描述性科学演变为越来越关注其观测结果背后的机理的地球化学。如今，地球化学已细分为许多子领域，包括水成地球化学，宇宙化学，无机地球化学，同位素地球化学，有机地球化学和微量元素地球化学。由于大多数地质过程都涉及化学反应，因此地球化学和地球化学数据也被用来解释地球科学其他领域中的许多过程.1952年以来，在加州理工学院的G
In addition to general Institute and basic division requirements, candidates for the Ph.D. degree in geochemistry are required to take one term of Ge 109 in the geochemistry option and are required to demonstrate an understanding of the field through a total of 90 units of course work at the 100 level or higher spread over four of the subdisciplines offered in the option: petrology/mineralogy, isotope geochemistry, cosmochemistry, water chemistry/oceans, atmospheres, biogeochemistry, or advanced chemistry. A student with substantial prior experience in some of the subdisciplines may use prior course work to substitute up to 45 of these units with the approval of the geochemistry option representative. In the oral candidacy exam, the student will be subject to examination in all four of the chosen subdisciplines. All students must have a basic knowledge of chemistry at the level of Ch 21 and mathematics at the level of Ge 108.