There are others, such as methane, which has a shorter life span but traps heat more effectively.

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The filter material developed by Nikolaidis and his colleagues, with funding from the Critical Technologies Program and industry, has at least a 20-year life span.

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But bacteria and viruses breed fast, so natural selection has time, within the span of a human life, to make a difference.

ECONOMIST: Evolution: Beetle drive | The

Later in the period, the Capitals did, twice with ease in a 46-second span to win, 3-1, and give life to a question that has hounded the Rangers for years: Why is their power play so lousy?

WSJ: The Rangers' Power Is Out

In mammals, this kind of epigenetic modification has been assumed to last only during the life span of a particular animal, because such changes are usually erased in the sperm and egg cells.

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