Scientists may not need to explore outer space to find 'alien' biology, cosmologist says.

When ET phones home, he may not have to make a long-distance call.

Forms of life different from the organisms humans are familiar with may exist on this planet already, says cosmologist Paul Davies of Arizona State University in Tempe. At a news conference on February 14 at the annual meeting of American Association for the Advancement of Science, Davies and other scientists interested in identifying alien life-forms called for a "mission to Earth" to discover "life as we don't know it."

Many scientists used to believe that life was statistically improbable. In recent decades that view has shifted, and many now think that life may exist all over the universe. If it is possible to find life on other Earth-like planets, then "weird" or "shadow" life might already exist on Earth, Davies says.

But Davies insists that he's not calling for a big, expensive project to look for aliens on Earth.

"This isn't anything that requires a massive undertaking. It's not like the human genome project," he says. "I'm trying to change the way people think." He is calling on scientists surveying microbial diversity to extend searches to include weird life.

For instance, a project to catalog viruses in the ocean could include a search for viruses that incorporate arsenic instead of phosphorus in DNA, he says. Such arsenic viruses could indicate that there is arsenic-based life on the planet.