(Undated) -- Earth may be heading toward mass extinction. That's the startling conclusion of a series of articles appearing today in the journal "Science." A special section on "Vanishing Fauna" notes the steady decline of the world's forests and animal species because of human activity. Researchers say such global loss of plants and animals continues to drive the trend toward extinction. Scientists conclude that reversing that trend is becoming increasingly difficult because of the major damage being done to the Earth's ecosystem.