Washington, November 21 Scientists have determined that colorful cave deposits found on the walls of lava tubes, long thought to be ordinary minerals, are actually mats of waste excreted by previously unknown types of microbes, a discovery that offer clues in the search for life on Mars and beyond.

According to a report in National Geographic News, the microbes were found on the walls of lava tubes in Hawaii, New Mexico, and the Portuguese Azores islands, a volcanic archipelago in the Atlantic Ocean.

The finds include "a lovely blue-green ooze dripping out of the (cave) ceiling in Hawaii; a vein of what looks like a gold, crunchy mineral in New Mexico; and, in the Azores, amazing pink hexagons," said Diana Northup, a geomicrobiologist at the University of New Mexico.

"That's the waste-the bug poop, if you will," she added.

Lava tubes form when molten lava seeps out beneath a solidifying flow from an active volcano, leaving long caves in its wake.

Since 1994, Northup and colleagues have been seeking out unusual deposits in caves, including lava tubes, and putting them under a microscope or testing them for DNA.

"Her team's discoveries add to a growing body of evidence that lava tubes on other planets might be the best places to look for signs of extraterrestrial life," said Saugata Datta, a geochemist from Kansas State University. n 2007, pictures from a Mars orbiter showed dark holes that appear to be places where lava-tube roofs have collapsed.

"Caves are a unique environment where we think that minerals precipitating out of liquids and microbial growth are enhanced by stable physical and chemical conditions," Datta said.

On Mars, water could have percolated into subterranean caves long ago, possibly bringing with it a banquet of minerals that could have fed ancient microbes.

Also, the insides of such caves would have remained sheltered from harsh surface conditions, giving any possible Martian fossils a better shot at long-term survival.

Now that scientists know what cave-dwelling microbes leave behind, it's possible future Mars missions might search for similar traces of life in the red planet's caves.

"Diana is essentially providing a field guide as to what you might find in these things," said New Mexico Institute of Mining and Technology's Boston.

"It's very clear from our work in all different kinds of caves on this planet that the interior of a cave can be radically different from the external environment," she added.

"That might be the case on Mars, as well," she said. (ANI)