Prior to 1965 geologists assumed that the two giant rock plates meeting at the San Andreas Fault generate heat through friction as they grind past each other, but in 1965 Henyey found that temperatures in drill holes near the fault were not as elevated as had been expected. Some geologists wondered whether the absence of friction-generated heat could be explained by the kinds of rock composing the fault. Geologists' pre-1965 assumptions concerning heat generated in the fault were based on calculations about common varieties of rocks, such as limestone and granite; but "weaker" materials, such as clays,had already been identified in samples retrieved from the fault zone. Under normal conditions, rocks composed of clay produce far less friction than do other rock types.

    In 1992 Byerlee tested whether these materials would produce friction 10 to 15 kilometers below the Earth's surface. Byerlee found that when clay samples were subjected to the thousands of atmospheres of pressure they would encounter deep inside the Earth, they produced as much friction as was produced by other rock types. The harder rocks push against each other, the hotter they become; in other words, pressure itself, not only the rocks' properties, affects frictional heating. Geologists therefore wondered whether the friction between the plates was being reduced by pockets of pressurized water within the fault that push the plates away from each other.

    Recently biologists have been interested in a tide-associated periodic behavior displayed by the diatom Hantzschia virgata, a microscopic golden-brown alga that inhabits that portion of a shoreline washed by tides (the intertidal zone). Diatoms of this species, sometimes called "commuter" diatoms, remain burrowed in the sand during high tide, and emerge on the sand surface during the daytime low tide. Just before the sand is inundated by the rising tide, the diatoms burrow again. Some scientists hypothesize that commuter diatoms know that it is low tide because they sense an environmental change, such as an alteration in temperature or a change in pressure caused by tidal movement. However, when diatoms are observed under constant conditions in a laboratory, they still display periodic behavior, continuing to burrow on schedule for several weeks. This indicates that commuter diatoms, rather than relying on environmental cues to keep time, possess an internal pacemaker or biological clock that enables them to anticipate periodic changes in the environment. A commuter diatom has an unusually accurate biological clock, a consequence of the unrelenting environmental pressures to which it is subjected; any diatoms that do not burrow before the tide arrives are washed away.

    This is not to suggest that the period of this biological clock is immutably fixed. Biologists have concluded that even though a diatom does not rely on the environment to keep time, environmental factors—including changes in the tide's hydrostatic pressure, salinity, mechanical agitation, and temperature—can alter the period of its biological clock according to changes in the tidal cycle. In short, the relation between an organism's biological clock and its environment is similar to that between a wristwatch and its owner: the owner cannot make the watch run faster or slower, but can reset the hands. However, this relation is complicated in intertidal dwellers such as commuter diatoms by the fact that these organisms are exposed to the solar-day cycle as well as to the tidal cycle, and sometimes display both solar-day and tidal periods in a single behavior. Commuter diatoms, for example, emerge only during those low tides that occur during the day.

    A key decision required of advertising managers is whether a "hard-sell" or "soft-sell" strategy is appropriate for a specific target market. The hard-sell approach involves the use of direct, forceful claims regarding the benefits of the advertised brand over competitors' offerings. In contrast, the soft-sell approach involves the use of advertising claims that imply superiority more subtly

    One positive aspect of the hard-sell approach is its use of very simple and straightforward product claims presented claims presented as explicit conclusions, with little room for confusion regarding the advertiser's message. However, some consumers may resent being told what to believe and some may distrust the message. Resentment and distrust often lead to counterargumentation and to boomerang effects where consumers come to believe conclusions diametrically opposed to conclusions endorsed in adverrising claims, By contrast, the risk of boomerang erects is greatly reduced with soft-sell approaches. One way to implement the soft-sell approach is to provide information that implies the main conclusions the advertiser wants the consumer to draw, but leave the conclusions themselves unstated. Because consumers are invited to make up their own minds, implicit conclusions reduce the risk of resentment ,distrust, and counter argumentation.

    Recent research on consumer memory and judgment suggests another advantage of implicit conclusions. Beliefs or conclusions that are self-generated are more accessible from memory than beliefs from conclusions provided explicitly by other individuals, and thus have a greater impact on judgment and decision making. Moreover, self-generated beliefs are often perceived as more accurate and valid than the beliefs of others, because other individuals may be perceived as less less knowledgeable, or may be perceived as manipulative or deliberately misleading. Despite these advantages, implicit conclusions may mot always be more effective than explicit Conclusions. One risk is that some consumers may fail to draw their own conclusions and thus miss the point of the message. .Inferential activity is likely only when consumers are motivated and able to engage in effortful cognitive processes. Another risk is that some conSummers may draw conclusions Other than the one intended ,Even if inferential activity is likely there is no guarantee that consumers will follow the path provided by the advertiser. Finally, a third risk is that consumers may infer the intended conclusion but question the validity of their inference.