All of us on Earth – from the tiniest amoeba to the most majestic gray whale – might be alien invaders.

One scientist is presenting a new twist on a perennially popular theory, called "panspermia," that life on this planet might have been planted by meteorites that slammed into an ancient Earth. Chemist Steven Benner, who works at the Foundation for Applied Molecular Evolution, argues in a presentation delivered Thursday at the Goldschmidt Conference in Italy that the earliest building blocks of life couldn’t have survived on Earth at the time – but they could have arisen on Mars.

The theory rests on the assumption that the evolution of life began with simple biopolymers, like RNA. But there are multiple reasons why the conditions on Earth billions of years ago wouldn’t have been hospitable to these tiny bits of organic material. RNA isn’t very stable on its own; add some energy, like heat or light, and it devolves into a goopy, oily glob. Benner calls this the “tar paradox.”

Certain elements, like boron and molybdenum, can mitigate this tendency for organic materials to dissolve into tar. But these minerals typically form in dry, desert areas, and Earth at the supposed time of RNA emergence was completely waterlogged (which presents yet another problem, as RNA also has a tendency to dissolve in water).

“If Earth was too young for borate… and too wet for deserts, then life could not have emerged on Earth,” Benner wrote in an email.

However, scientific analyses of Martian meteorites show that the Red Planet once had the necessary elements to keep RNA sticking together: boron and oxidized molybdenum.

“Mars has always been more oxidizing and drier than Earth,” Benner wrote in an email. “True, being too small to have a magnetic field, it has lost most of its atmosphere and most of its water. However, 3.5 billion years ago, all of the chemistry that we propose could have happened on Mars. As Mars became less and less habitable over time, the life that originated on Mars (and, in this view, could not have originated on Earth), escaped to Earth, which has remained habitable until this day.”

Still, some scientists point out that at the moment, Benner’s theory doesn’t have a huge amount of evidence to support it. While the theory is fairly plausible, according to Denver Museum of Nature and Science astrobiologist David Grinspoon, plausibility isn’t proof.

"This isn't really evidence that life came from Mars, but it is evidence that Steven Benner is very clever," Grinspoon told NBC News.

Benner is no credulous quack – he was one of the earliest people to question a later-discredited study that purported to show evidence of arsenic-based life. He acknowledges the limits of his theory.

“This ‘story’ illustrates in particular the difference between a locale where life can survive and a locale where life can emerge,” he wrote. “The two are different.”