SCIENCE'S COMPASS I find that graduate students in the sci- ences, at one time myself included, tend not to realize just how well they are being preparedfor any conceivable career choice. It seems that the trauma of the graduate school-postdoctoral daze must first be giv- en time to subside before most can appreci- ate the universality of their training. Some self-inspection is necessary, as Gale im- plies, to realize that academic appoint- ments are just one among the many re- warding ways to translate these increasing- ly valuable skills into a livelihood. T.J. Murphy Department of Pharmacology,Emory University School of Medicine, Atlanta, GA 30322, USA. E- mail: tmurphy@pharm.emory.edu Environmental Health: Nickel-and-Diming It Researchers in environmental toxicology should endorse the argument advanced by B. M. Lester, L. L. LaGasse, and R. Seifer (Policy Forum, Science's Compass, 23 Oct., p. 633) on how to interpret the out- come of cocaine abuse during pregnancy. A predicted epidemic of "crack babies" never materialized. Instead, they note, the offspring exhibit subtle deficiencies such as IQ reductions of about 3%. Although small magnitude, it is a gap with vital pub- lic health and policy implications that even many scientists fail to appreciate. I urged such a perspective for neurotoxi- city risk assessment some time ago (1) and for grasping the consequences of maternal drug abuse (2). The definition of excessive lead exposure in children is now based largely on shifts in the population distribu- tion of IQ scores (3), as are many of the eco- nomic benefits flowing from the removal of lead from gasoline (4). The debate about the health risks of methyl mercury in fish is es- sentially a debate about similar shifts in measures of neurobehavioral development (ScienceScope, 18 Sept., p. 1779). The health risks of polychlorinated biphenyls (PCBs) and endocrine disruptors can be viewed from the same vantage point (5). En- vironmental health protection, so to speak, is a nickel-and-dime business. Bernard Weiss Departmentof Environmental Medicine, U niversi- ty of RochesterSchool of Medicineand Dentistry Rochester, NY 14642, USA. E-mail: weiss@en- vmed.rochester.edu References 1. B. Weiss, Trends Pharmacol. Sci. 9, 59 (1988). 2. - in Cocaine Mothers and Cocaine Babies: The Role of Toxins in Development, M. Lewisand M. Ben- dersky, Eds. (Ertbaum, Hillsdale, NJ, 1995), pp.41-55. 3. Centers for Disease Control, Preventing Lead Poisoning in Young Children (U.S. Department of Health and Hu- man Services,Washington, DC, 1991). 4. The Benefits and Costs of the Clean Air Act, 7970 to 1990 (U.S. Environmental Protection Agency, Washing- ton, DC, 1996). 5. B.Weiss, Neurotoxicology 18, 581, (1997);J. L.Jacobson and S. W. Jacobson, N. Engl. J. Med. 335,783 (1996). An Early Snowball Earth? In their article "A Neoproterozoic snowball Earth" (Reports, 28 Aug., p. 1342), Paul F. Hoffman et al. report that global ice-house conditions existed during the Proterozoic, as inferred from negative carbon isotopes in carbonate rocks from Namibia. These conditions are said to have led to the near termination of life on Earth. In summary, the hypothesis suggests that global glaciation existed until volcanic outgassing increased carbon dioxide (CO2) concentrations to 120,000 parts per mil- lion of volume, at which time the global ice-house conditions collapsed. Several is- sues of geology and climate, however, re- main unresolved. First, how did global glacial conditions come about? Reduced solar forcing could not have been the cause, because the solar constant was lower before the breakup of the Rodinia supercontinent.A positive ice- albedo feedback triggered by reduced CO2 A I ~~~~~~~~ CircleNo. 18 on Readers' Service Card 1644 27 NOVEMBER 1998 VOL 282 SCIENCE www.sciencemag.org