The team, led by the University of Sheffield, found small organisms that could have come from space after sending a specially designed balloon to 27 km into the stratosphere during the recent Perseid meteor shower.
"Most people will assume that these biological particles must have just drifted up to the stratosphere from Earth, but it is generally accepted that a particle of the size found cannot be lifted from Earth to heights of, for example, 27 km," said Professor Milton Wainwright from the University's Department of Molecular Biology and Biotechnology.
"The only known exception is by a violent volcanic eruption, none of which occurred within three years of the sampling trip.
"In the absence of a mechanism by which large particles like these can be transported to the stratosphere we can only conclude that the biological entities originated from space.
"Our conclusion then is that life is continually arriving to Earth from space, life is not restricted to this planet and it almost certainly did not originate here," he said.
"If life does continue to arrive from space then we have to completely change our view of biology and evolution. New textbooks will have to be written!" Wainwright said.
The balloon, designed by Chris Rose and Alex Baker from the University of Sheffield's Leonardo Centre for Tribology, was launched near Chester and carried microscope studs which were only exposed to the atmosphere when the balloon reached heights of between 22 and 27 km.
The balloon landed safely and intact near Wakefield. The scientists then discovered that they had captured a diatom fragment and some unusual biological entities from the stratosphere, all of which are too large to have come from Earth.
Wainwright said stringent precautions had been taken against the possibility of contamination during sampling and processing, and said the group was confident that the biological organisms could only have come from the stratosphere.
The findings have been published in the Journal of Cosmology.
Wainwright's team is hoping to extend and confirm their results by carrying out the test again in October to coincide with the upcoming Haley's Comet-associated meteorite shower when there will be large amounts of cosmic dust.