Life on Earth was kick-started thanks to a key mineral deposited by a meteorite from Mars, according to a novel theory aired on Thursday.

The vital ingredient was an oxidised mineral form of the element molybdenum, which helped prevent carbon molecules -- the building blocks of life -- from degrading into a tar-like goo.

The idea comes from Steven Benner, a professor at the Westheimer Institute for Science and Technology in Gainesville, Florida, who was to present it at an international conference of geochemists in Florence, Italy.

"It's only when molybdenum becomes highly oxidized that it is able to influence how early life formed," Benner said in a press release.

"This form of molybdenum couldn't have been available on Earth at the time life first began, because three billion years ago the surface of the Earth had very little oxygen, but Mars did."

In this violent epoch of the Solar System, the infant Earth was pounded by comets and asteroids.

Mars, too, would have come under bombardment, and the impacts would have caused Martian rubble to bounce into space, where they would have lingered until eventually being captured by Earth's gravity.

Recent analysis of a Martian meteorite showed the presence of molybdenum, as well as a boron, an element that would also have helped nurture life by helping to protect RNA -- a primitive cousin to DNA -- from the corrosive effects of water.

"The evidence seems to be building that we are actually all Martians, that life started on Mars and came to Earth on a rock," said Benner.

"It's lucky that we ended up here nevertheless, as certainly Earth has been the better of the two planets for sustaining life. If our hypothetical Martian ancestors had remained on Mars, there might not have been a story to tell."

Other theories about how life began on Earth suggest that water, the key ingredient, was brought by comets, famously dubbed "dirty snowballs," which comprise ice and dust left from the building of the Solar System.

Another hypothesis, called panspermia, suggests bacteria hitched a ride on space rocks, splashing into Earth's warm and welcoming sea.