The Paleogene is a time of major change in global climate that holds critical information for understanding Earth system processes. The entire Paleogene was a period of extreme warmth when compared to modern climate conditions; the study of the Paleogene is thus pertinent to understand the processes that maintain warm Earth conditions.

ODP Leg 199 is the first drilling leg to study the Paleogene equatorial Pacific using modern scientific drilling technology. Study of the continuously recovered sections has been important for fundamental advances in Cenozoic chronostratigraphy and to understand Cenozoic motion of the Pacific plate. The first continuous sedimentary sections of Oligocene and middle–late Eocene age from the equatorial Pacific have been extremely important to understand major paleoceanographic events regionally as well as globally. Postcruise science from Leg 199 has developed precise timing of some of the first major Cenozoic glaciations and identification of transient, probably glacial, events within the Eocene.

Fundamental new information about global climate, the carbon cycle, and Cenozoic paleoproductivity has resulted from the study of Leg 199 sediments, but many new questions have appeared. What really is the relationship global warmth, weathering, and the carbon cycle? To what extent does global warmth regulate carbon burial? How can deep circulation reorganize itself in response to climate? Further work on Leg 199 sediments will help to answer these questions, especially when combined with further drilling that targets the Paleogene.