Since these characteristics make life on Earth possible, scientists have long assumed they are required for life elsewhere in the universe.
But advances in biology and biochemistry in the last decade show that the basic requirements for life may not be so concrete, according to Baross.
Seth Shostak is a senior astronomer at the SETI Institute in Mountain View, California, which is dedicated to the search for alien life. He was not part of the report but said the premise is "very justified."
For example, he said, the Viking lander missions to Mars in the 1970s were controversial, because although they did not find life, they only looked for Earthlike life.
(Read related story: "Viking Mission May Have Missed Mars Life, Study Finds" [October 23, 2006].)
"Let's be a little more broad-minded. Let's not just look for life as we know it," Shostak said.
"The only problem," he added, "is it's very difficult to look for life as you don't know it, because you don't know how to look for it. I think that's what motivates this study."
According to the report, the search for life elsewhere in the solar system and beyond should include efforts to detect "weird" forms of life.
For example, laboratory experiments have recently demonstrated that scientists can change the DNA of Earth organisms, which then continue to encode the new genetic information.
The findings suggest that "a different life-form doesn't necessarily have to have exactly the same chemistry that Earth life has," Baross said.
Even weirder life, he said, may tap into different sources of energy than the sun, which most Earth organisms depend upon.
Perhaps most intriguing, Baross continued, is the possibility that extraterrestrial life could thrive on a solvent other than water, such as the liquid methane and ethane on Titan.
(Read related story: "Saturn Moon Has Lakes, "Water" Cycle Like Earth's, Scientists Say" [January 5, 2007].)
"Could a carbon-based life-form survive and live in that?" Baross said.
"That's pretty much an unknown to Earth life."
Finding Weird Life
The hunt for weird life on other planets and moons begins with studying life on Earth, Baross explained. For example, one of the biggest unanswered questions about Earth life is how it originated.
"What comes out of this report is that there's so much about Earth life that we don't understand," Baross said.
This is especially true about life forms that exist in extreme environments like arid deserts, high-altitude lakes, and snuggled up against boiling deep-sea vents.
"The possibility exists that there are still organisms that can tell us something about early life and even possibly the origin of life that we haven't really tapped into," Baross said.
The lessons learned from Earth's weird life can then guide the search for even weirder life elsewhere in the universe, the researchers noted.
Free Email News Updates
Sign up for our Inside National Geographic newsletter. Every two weeks we'll send you our top stories and pictures (see sample).
SOURCES AND RELATED WEB SITES