The Oldest Earth and Moon Rocks

Introduction: We describe a project that could greatly alter our understanding of the environment on Earth at the time in which life originated. The approach is to systematically search for terrestrial rock and mineral samples that should be present on the lunar surface due to impacts, and in selected terrestrial localities. Project activities include studies of terrestrial materials, development of methods to systematically sample impact ejecta on the Moon, and ultimately , deployment of search methods on the Moon with both unmanned landing craft and as part of a lunar outpost. Activities could proceed in parallel to the anticipated development of robotic lander and manned missions to the Moon. Motivation: The Hadean Eon (4.5-4.0 Ga) is the dark age of Earth history; there is no known rock record from this period. Detrital zircons as old as nearly 4.4 Ga permit some insights into this phase of Earth history. However, many important questions cannot be addressed outside of the rock context (e.g., redox conditions , geothermal gradient, evidence of biologic activity). Extensive investigation of the quartzites host-ing ancient detrital zircons have not revealed a single lithic fragment, let alone a Hadean crystalline rock. Yet this is the period when life likely first developed on Earth, and, unless it was extinguished by impacts, this life was ancestral to Earth life today. We propose to take advantage of the lunar exploration initiative to discover ancient terrestrial rocks preserved on the Moon. Studies of the geochemical evolution of the Moon itself also offers promise as means for reconstructing the earliest epoch of solar system evolution including testing models of lunar formation. The nature of the late heavy bombardment has profound implications for the role that chaotic orbital dynamics may have on the development of life (frustration) and, more broadly, the role of giant planet migration in contributing to an inhospitable environment. We see four opportunities: 1) Identification and return of terrestrial rocks from the lunar regolith via ISRU activities; 2) The lunar initiative may allow either robotic landings or human sorties to gather key samples; 3) With the certainty of a return to the Moon, constraints on the use of the current lunar samples can be relaxed in order to better prepare for the new activity; 4) Specific isotopic studies of old terrestrial and lunar zircons. Background: The Moon is the only accessible body in the solar system that preserves rocks formed