Scientists believe they have found the first evidence of life arriving to Earth from space, which could "completely change our view of biology and evolution".
The team, from the University of Sheffield, made the discovery after sending a balloon high into the stratosphere.
On its return they found organisms that were too large to have originated from Earth.
Professor Milton Wainwright, who led the team, said the results could be revolutionary.
The balloon was launched near Chester and carried microscope studs which were only exposed to the atmosphere when it reached heights of between 22 and 27km from the planet.
It later landed safely and intact near Wakefield when scientists discovered they had captured a fragment of biological material, which were unusual due to their size.
– Professor Milton Wainwright, department of molecular biology and biotechnology
If life does continue to arrive from space then we have to completely change our view of biology and evolution.
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.
The professor 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.
– Professor Wainwright, Sheffield University
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, 27km.
The only known exception is by a violent volcanic eruption, none of which occurred within three years of the sampling trip.
The findings have been published in the Journal of Cosmology and updated versions will appear in the same journal, a new version of which will be published in the near future.
The team is hoping to extend and confirm their results by carrying out the test again next month to coincide with the Haley's Comet-associated meteorite shower, when there will be large amounts of cosmic dust.
It is hoped that more new, or unusual, organisms will be found.