"We were able to conclude there were viable microorganisms present at different heights in the air," Chandra Wickramasinghe, of Cardiff University's Center for Astrobiology, told United Press International.
Wickramasinghe's team reported last year they had discovered microorganisms high above the Earth, but they had been unable to grow them in the lab. So they turned to microbiologist Milton Wainwright of the University of Sheffield, England.
He was able to isolate and grow a fungus and two species of bacteria that were collected 25 miles above the planet's surface. The new findings are reported in the December issue of the Federation of European Microbiological Societies Microbiology Letters.
"The findings support the idea of panspermia, the theory that comets not only brought the first living microorganisms to Earth 4 billion years ago but that they must also be doing that at the present time," said Wickramasinghe, a co-author of the theory.
The microbes are not new species and "they're extremely closely related to known Earth bacteria but that's what the theory of panspermia predicts," because it holds that bacteria on Earth originated from space, he said.
The microorganisms are unlikely to be due to contamination because there are no conditions on the planet under which bacteria can be lifted so high above the surface, he said. In addition, the researchers were very meticulous when collecting the samples to ensure there was "no chance of anything of contaminants being included in the collection," he said.
Wickramasinghe's group is conducting studies of the ratio of carbon isotopes in the bacteria. "If they came from outer space, they should have a different ratio (of carbon isotopes) than that on the Earth," he said. Those results should be available in the next several months.
Other scientists in this field were skeptical of the claims that the microbes came from outer space.
Hojatolla Vali, a professor at McGill University who was involved in the discovery of evidence of bacteria in a meteorite from Mars, told UPI: "I tend to say the microbes are coming from Earth and going up."
Panspermia is a controversial issue, he said, "because we don't really have any evidence yet that there is any life found on meteorites or other planets."
He added that he had authored a study that "concluded that meteorites are capable of transferring life between planets" but no one has ever found any evidence this occurred.
Even in the Mars meteorite, he said, scientists only found indications -- not direct evidence -- bacteria might have been present. Also, there is no evidence the bacteria were alive when the meteorite arrived on Earth, he said.
Vali added that bacteria "can survive in very, very harsh conditions," including 3 miles below Earth's surface and in the permafrost layers where the temperature is below zero.
So "it is reasonable to conclude that bacteria can survive the harsh conditions at (25 miles)," he said.
(Reported by Steve Mitchell, UPI Medical Correspondent, in Washington.)