Washington: Life existed long before Earth came into being, and may have originated outside our solar system, scientists claim.
Researchers say life first appeared about 10 billion years ago - long before Earth, which is believed to be 4.5 billion years old.
Geneticists have applied Moore`s Law - observation that computers increase exponentially in complexity, at a rate of about double the transistors per integrated circuit every two years - to the rate at which life on Earth grows in complexity.
Alexei Sharov of the National Institute on Ageing in Baltimore, and Richard Gordon of the Gulf Specimen Marine Laboratory in Florida, replaced the transistors with nucleotides - the building blocks of DNA and RNA - and the circuits with genetic material.
Their findings suggest life first appeared about 10 billion years ago, far older than the Earth`s projected age of 4.5 billion years.
Like in the 2012 sci-fi movie Prometheus, as our solar system was forming, pre-existing bacteria-like organisms, or even simple nucleotides from an older part of the galaxy, could have reached Earth by hitching an interstellar ride on comets, asteroids or other inorganic space debris.
However, the calculations are not a scientific proof that life predates Earth - there`s no way of knowing for sure that organic complexity increased at a steady rate at any point in the universe`s history.
"There are lots of hypothetical elements to (our argument) ... But to make a wider view, you need some hypothetical elements," Sharov said.
Sharov said that if he had to bet on it, he`d say "it`s 99 per cent true that life started before Earth - but we should leave one per cent for some wild chance that we haven`t accounted for."
The theory of "life before Earth," if found true, debunks the long-held science-fiction trope of the scientifically advanced alien species.
Moreover, if genetic complexity progresses at a steady rate, then the social and scientific development of any other alien life form in the Milky Way galaxy would be roughly equivalent to those of humans, the report said.
"Contamination with bacterial spores from space appears the most plausible hypothesis that explains the early appearance of life on Earth," researchers said.