In this paper we present a time-stratigraphic scheme and geologic time scale for the protoplanet Vesta, based on global geologic mapping and other analyses of NASA Dawn spacecraft data, complemented by insights gained from laboratory studies of howardite–eucrite–diogenite (HED) meteorites and geophysical modeling. On the basis of prominent impact structures and their associated deposits, we pro...

After more than 30 years of international research and development, there is a broad technical consensus that geologic disposal of highly-radioactive waste will provide for the safety of humankind and the environment, now, and far into the future. Safety analyses have demonstrated that the risk, as measured by exposure to radiation, will be of little consequence. Still, there is not yet an oper...

Geologic process, including tectonics and global climate change, profoundly impact the evolution of life because they have the propensity to facilitate episodes of biogeographic differentiation and influence patterns of speciation. We investigate causal links between a dramatic faunal turnover and two dominant geologic processes operating within Laurentia during the Late Ordovician: the Taconia...

Amazonian The youngest of the geologic epochs on Mars identified through geoiogic mapping of superposition relations, and the area! density of impact craters. caldera An irregular collapse feature formed over the evacuated magma chamber within a volcano. central volcano Emplacement of volcanic materials from a centralized source vent rather than along a distributed line of vents, composite volc...

As part of a 3.year program of geologic mapping from the Yukon border south through the Midway, Cassiar and Erickson mining camps (Nelson and Bradford, 1987a; 1987b; 1989, this volume; Nelson et al. 1988a; 1988b), I:25 000.scale mapping was conducted in the northeast quarter of the Needlepoint Mountain (104P/4) map area during the 1988 field season (Figure l-35-1). Since Gabrielse’s ( 1963) ori...

PRD1, an icosahedra-shaped, 62 nm (diameter), double-stranded DNA bacteriophage with an internal membrane, has emerged as an important model virus for studying the manner in which microorganisms are transported through a variety of groundwater environments. The popularity of this phage for use in transport studies involving geologic media is due, in part, to its relative stability over a range ...

National geologic map databases are presently being constructed in the U.S. and Canada, as well as in several other countries. Here, we describe an object-based model for geologic map information, specifically designed to represent digital geologic maps and related geoscientific information. Although oriented to geoscience, several fundamental issues in representing geospatial information are e...