Geological rhythms and cometary impacts

Time-series analysis reveals two dominant, stable long-term periodicities approximately equal to 33 +/- 3 and 260 +/- 25 million years in the known series of geological and biological upheavals during the Phanerozoic Eon. Because the cycles of these episodes agree in period and phase with the cycles of impact cratering on Earth, these results suggest that periodic comet impacts strongly influence global tectonism and biological evolution. These two periodicities could arise from interactions of the solar system with interstellar clouds as the solar system moves cyclically through the Galaxy.     

Leaf herbivores decrease fitness of a tropical plant

Damage by insect herbivores to neighboring individuals of the shrub Piper arieianum in a neotropical wet forest varies greatly. This differential damage has a genetic basis and results in a 2-year decrease in growth, seed production, and seed viability, with larger plants recovering before smaller plants. The results provide evidence that leaf herbivores represent a potentially strong selective force for the evolution of plant defenses.     

Polychlorinated Dibenzo-p-dioxins and Dibenzofurans in Sediments from Siskiwit Lake, Isle Royale

Polychlorinated dibenzo-p-dioxins and dibenzofurans were found in sediment from Siskiwit Lake on Isle Royale, Lake Superior, a location which can receive only atmospheric inputs. The source of these compounds is the atmospheric transport of dioxins and furans formed by combustion of domestic and chemical waste.     

Early eocene vertebrates from baja california: evidence for intracontinental age correlations

Newly discovered fossils support a Wasatchian (early Eocene) age for the Punta Prieta vertebrate fauna of Baja California and reveal the utility of land mammal ages on a continental scale. Dispersal scenarios for late Paleocene and early Eocene vertebrates usually invoke heterochrony for similar, but geographically separated, faunas or taxa. Such heterochrony is not supported by independent geochronologies or adequate geographic samples.     

Scientific communication and national security in 1984

The federal government's concern about maintaining the lead of the United States over the Soviet Union and its allies in militarily critical technology has led it to attempt to control unwanted technology transfer. Its attempts have extended to control of open scientific communication as well as the transfer of physical devices and blueprints. In 1982, the Corson Panel (an independent ad hoc committee) reviewed the evidence on the costs and benefits of controls and suggested guiding principles for government policy. This article examines the major policy developments since the Corson Panel completed its work. The stringency and the reach of government restrictions, either proposed or in force, go considerably beyond the panel's recommendations.