What are epidemiological studies, and what is their value? Are there any disadvantages to epidemiological studies?
What will be an ideal response?
They involve large-scale comparisons among groups of people, usually contrasting a group known to have been exposed to a toxicant with a group that has not. They allow for the risk of exposure to a toxicant to be determined. They are realistic, but a long time is required for the results of the studies to be determined. Furthermore, they do not address future effects of new products. Results of epidemiological studies must be interpreted cautiously because many factors affect health, and results do not determine cause and effect; they only measure statistical association.
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Ocean sediments and volcanoes are sources of:
a. Nitrogen b. Oxygen c. Sulfur d. Phosphorus e. both sulfur and nitrogen
Which type of radiation is being emitted in the following incomplete nuclear equation:
Pb ? 
Bi + ??
A. gamma B. beta C. alpha D. A and B E. none of the above
Which one of the following best illustrates a nonpoint source of pollution?
A) Oil leaking into the ocean from an oil rig B) Wastewater from a coal-fired power plant C) Storm-water drainage from the parking lot around a football stadium D) Raw sewage released into a river when storm-water overflows a city's sewage treatment facility
Modern geochronology studies recognize that most radiometric dates record a time when a mineral cools below a temperature where the mineral closes to gain or loss of parent and daughter isotopes
This "closure temperature" varies between different minerals and different isotopic systems. This has allowed the absolute dating of sedimentary rocks through dating of single crystals. For example, if a rock is heated above the closure temperature of the rocks constituent minerals, the date of that mineral provides a minimum age. In contrast, if the rock contains a mineral with a closure temperature higher than the maximum temperature reached by the rock, that mineral will retain the age from its source. The mineral zircon dated by U-Pb methods is an example. So, you look at a rock that has Cretaceous fossils in it, but your paleontologist friend looks at them and cannot determine if they are Early or Late Cretaceous in age. The rock contains the mineral apatite, which accumulates He through the decay or U and Th, but closes to He loss at temperature of around 75°C. You know from the stratigraphic section that the rocks were originally buried at least 3km. The local geothermal gradient is about 35°C/km. You obtain an apatite He date of 105 +/- 2 million years. You also date 100 grains of zircon from the rock. The zircons yield dates that range in age from 2.1 billion years to 125 million years. Three different zircon grains yield ages between 125 and 127 million years. You google "cretaceous time scale" and learn that the Cretaceous begins at about 144 million years and ends at about 65 million years ago. The Early Cretaceous ends about 100 million years ago. How old are these sedimentary rocks?