Extra-terrestrial microbes might have brought life to the Earth, say scientists.
The theory is based on calculations showing a high likelihood of rock fragments from planets in other star systems landing on the Earth long ago, the Daily Mail reported Wednesday.
Some of them could have carried embedded micro-organisms, according to experts writing in the journal Astrobiology.
The research suggests the dormant bugs could easily have survived the long journey through space, despite high levels of cosmic radiation, the Mail said.
Simple life may equally well have travelled from the Earth to planets outside the solar system, the scientists believe.
The process, known as lithopanspermia, could mean the universe is teeming with Earth-like life.
"Our work ... says that lithopanspermia might have been very likely, and it may be the first paper to demonstrate that," said lead researcher Edward Belbruno, from Princeton University in the US.