The tiny creatures are smaller than most commonly known bacteria and have endured at least 120,000 years in subzero temperatures, crushing pressure, low oxygen levels and almost no nutrients. They were found in ice core samples taken nearly 2 miles (3,000 meters) below a glacier. Researchers said they could be a million years old.

The microscopic critters are all less than 1 micron wide and some are less than 0.2 microns. Most bacteria, which also are too small to see without a microscope, are between 1 and 10 microns.

Scientists are still trying to figure out if newfound microbes -- there are several varieties -- were dormant or living normal, energy consuming lives.

"We are particularly interested in the formation of ultra-small cells as one possible stress-survival mechanism, whether they are starved, minute forms of known normal-sized microbes or intrinsically dwarf novel organisms, and also whether these cells are able to carry on metabolic processes while they are so highly stressed," said Penn State researcher Vanya Miteva.

The discovery was to be presented today at the 2004 General Meeting of the American Society for Microbiology in New Orleans, Louisiana.

The ancient organisms appear to be related to modern, ultra-small microorganisms found in other cold environments, said Jean Brenchley a professor of microbiology and biotechnology at the university.

Brenchley and Miteva examined the organisms' DNA and conducted several other tests. They speculate that other similarly diminutive microbes, less than 0.2 microns in size, might have been missed in previous research.

"It appears that these ultra-small microbes often are missed in research studies because they pass through the finest filters commonly used to collect cells for analysis," Miteva says.

That would make them part of the vast, "uncultured majority" of life, the 99 percent of all microbes on this planet that have yet to be isolated and "cultured," or prepared, for study, the researchers said.

Some of the newfound cells have been cultured and formed colonies of offspring, continuing the propensity to stay small.

"Our study of the abundance, viability, and identity of the ultra-small cells existing in the Greenland ice is relevant to discovering how small life-forms can be; how cells survive being small, cold, and hungry; and what new tricks we need to develop in order to cultivate these small cells," Miteva said in a statement.

The microbes may help define the very limits of life on Earth and elsewhere in the universe, the researchers said.