The NASA announcement created an enormous Internet buzz: The space agency was going to reveal Thursday "an astrobiology finding that will impact the search for evidence of extraterrestrial life."

Was the government about to say it had found liquid water on a moon of Jupiter? Microbes on Mars? Something even stranger -- say, ET?

Sci-fi bloggers speculated the announcement ``could prove the existence of aliens'' or ``the theory of shadow creatures that exist in tandem with our own.''

But then the announcement came and it was about . . . bacteria right here on Earth.

At a 2 p.m. news conference streamed live over the Web, scientists at the National Aeronautics and Space Administration said they found microbes in the mud beneath a California lake that can use arsenic -- usually considered toxic -- rather than phosphorus as one of the building blocks of its DNA. Phosphorus is one of the elements that sustains all other life forms on earth.

After their great anticipation, sci-fi fans were told the discovery might help cut pollution of waterways like Lake Okeechobee by replacing the phosphorus in fertilizers that run off into the lake, creating fish-choking algae blooms.

One of the NASA researchers acknowledged the frustration after the build-up: ``I can see you're disappointed, that some of you were expecting walking, talking aliens,'' said Felisa Wolfe-Simon, a NASA astrobiology researcher and co-author of the study.

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