Scientists have controversially claimed that life on Earth originated in space after plankton were found on the exterior of the ISS.
Earlier this week cosmonauts announced they had found the microorganisms living on one of the windows of the Russian segment of the space station.
And while the exact origin of these critters is still unknown, it has been claimed they may have come from outer space - supposedly like life on Earth.
Experiments have previously shown bacteria can survive outside our planet, but this is thought to be the first time more complex life has been found this far out in space.
Their exact origin is not yet known and will require further study - although it may just be contamination from the American segment of the ISS.
At the time of the discovery Russian experts said the tiny organisms were carried to the station on air currents from the sea where plankton is found in abundance.
Earlier this week cosmonauts announced they had found the microorganisms living on one of the windows of the Russian segment of the space station.
And while the exact origin of these critters is still unknown, it has been claimed they may have come from outer space - supposedly like life on Earth.
Experiments have previously shown bacteria can survive outside our planet, but this is thought to be the first time more complex life has been found this far out in space.
Their exact origin is not yet known and will require further study - although it may just be contamination from the American segment of the ISS.
At the time of the discovery Russian experts said the tiny organisms were carried to the station on air currents from the sea where plankton is found in abundance.
Russian cosmonauts claim to have found marine creatures living on the outside of the International Space Station where conditions for life are believed to be impossible
However others claim this is impossible, with another explanation being that the minute plants drifted onto the ISS from elsewhere in space.
They insist this supports theories that plankton - one of the earliest forms of life - must have originally fallen to earth from space billions of years ago. And say this is proof that we are all of extraterrestrial origin, a theory known as panspermia.
Professor Chandra Wickramasinghe, of the Buckingham Centre for Astrobiology, said algae-like organisms, or diatoms, have previously been found on meteorites which have fallen to Earth.
They insist this supports theories that plankton - one of the earliest forms of life - must have originally fallen to earth from space billions of years ago. And say this is proof that we are all of extraterrestrial origin, a theory known as panspermia.
Professor Chandra Wickramasinghe, of the Buckingham Centre for Astrobiology, said algae-like organisms, or diatoms, have previously been found on meteorites which have fallen to Earth.
'Diatoms have been found on meteorites in Sri Lanka, but there has been no proof where they actually came from,' he said.
'This is the first time that we have evidence that points towards complex living organisms falling from the skies to Earth.
Russia's launches into space take place from the Baikonaur Cosmodrome in Kazakhstan
'The space station is orbiting the earth in a total vacuum, there is no air, so it is a total defiance of the laws of physics to say these organisms were blown into space from Earth.
'The only explanation is that they have come from elsewhere in space, and this supports long-held theories that plankton, and therefore all life on Earth including humans, originated from organisms in space.
'Everything that we have on the Earth is derived from space, including humans.'
A controversial academic from the University of Buckinghamshire has claimed that plankton supposedly found on the exterior of the ISS (pictured) earlier this week are proof that life on Earth is of extraterrestrial origin. Professor Wickramasinghe says the plankton must have come from outer space
The discovery was made by Russian cosmonauts Olek Artemyev and Alexander Skvortsov while polishing the windows of the ISS during a spacewalk earlier this week.
They found the presence of plankton and other microorganisms using high-precision equipment.
The organisms are not native to Baikonur in Kazakhstan where the Russian modules of the station blasted off from so they could not have been carried into space from launch - although they could have been transferred from American parts of the station as Nasa's launches mostly take place near the Atlantic Ocean.
Experts had claimed that the plankton were not carried there at launch and must have been blown their on air currents, because they are marine microorganisms not indigenous to the Russian launch site in Kazakhstan. A SEM microscope view of one type of plankton (not discovered on the ISS) is pictured
'The results of this experiment are absolutely unique,' said Vladimir Solovyev, chief of the Russian ISS orbital mission.
'We have found traces of sea plankton and microscopic particles on the illuminator [window] surface. This should be studied further.'
'[Plankton] is found on the surface of the ocean. It isn’t characteristic to Baikonur [Cosmodrome, from where Russian launches to the space station take place].'
Professor Milton Wainwright, microbiologist at Sheffield University, said previous experiments conducted by his team found evidence of diatoms 17 miles (27km) above the Earth’s surface.
However he said this is the first time they have been detected so far out with the ISS more than 200 miles (250km) from the planet.
He said: 'This is an astonishing development and there is no other explanation other than these organisms came from space in the first place, they could not have blown up from the Earth.
Pictured is a Soyuz rocket carrying the crew of Expedition 31 to the ISS on 12 May 2012. Although it is not likely that plankton were been taken to the ISS from this location, it is possible that contamination from American launches may have spread organisms over the station
'This is the tipping point towards science proving that life is continually coming to Earth from space, and that it did so in the first instance.
'This is an amazing discovery, and there is now overwhelming evidence emerging that organisms on Earth came from outer space.'
Assembly of the International Space Station began in 1998 and today construction has effectively been completed.
Aside from housing astronauts to further humanity's space exploration efforts it also serves as a research laboratory for studies in biology, physics, astronomy and meteorology.
With regards to the plankton, Nasa has not yet confirmed whether similar findings have been made in the past, nor what their position is on the latest findings.
Professor Chandra Wickramasinghe is a leading proponent of panspermia, the hypothesis that life exists throughout the universe and is spread by asteroids and comets, in addition to simply drifting through the cosmos. Panspermia proposes that life forms that can survive the effects of space and travel vast distances
