On the Cover
July-August 2004 Volume 92, Number 4
The burning of plant material releases several gases, including the
ozone-destructive compounds methyl bromide and methyl chloride. This may
come as a surprise to some people, even to many scientists, who usually
think of these and other halogenated, carbon-containing molecules as
products of human industry. ...
Although best known as synthetic toxicants, thousands of halogen compounds are, in fact, part of our natural environment
Motor activity in the brain precedes our awareness of the intention to move, so how is it that we perceive control?
Bovine spongiform encephalopathy provides a case study in how to manage risks while still learning the facts
One theory prefers an accordion model; another has the continents travel the globe to reunite
A worldwide network of detectors may soon measure subtle ripples in spacetime itself, ushering in a new era of astrophysical research
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Maps of Time draws on the work of modern cosmologists, geologists, evolutionary biologists and archaeologists to trace history on the most immense scale imaginable
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