A goal of the Geosciences Network (GEON) is to develop cyber-infrastructure that will allow earth scientists to discover access, integrate and disseminate knowledge in distributed environments such as the Web, changing the way in which research is conducted. The earth sciences community has begun the complex task of creating ontologies to support this effort. A challenge is to coalesce the needs of the earth scientists, who wish to capture knowledge in a particular discipline through the ontology, with the need to leverage the knowledge to support technology that will facilitate computation, for example, by helping the composition of services. This paper describes an approach for defining workflow-driven ontologies that capture classes and relationships from domain experts and use that knowledge to support composition of services. To demonstrate the capability afforded by this type of ontology, the paper presents examples of workflow specifications generated from a workflow-driven ontology that has been defined for representing knowledge about gravity data.