H.G. Wells might not have been that far off when he wrote about aliens from Mars coming to Earth.
"It may not be likely," NASA researcher David Morrison told National Geographic News, "but we cannot exclude the possibility that we are, in effect, all Martians."
Panspermia, or the idea that Earth was "seeded" by life from outer space, is centuries old but until lately has not had much scientific evidence to support it.
But a European experiment last month demonstrates that microscopic life could indeed survive inside rocks hurtling through space.
A team led by John Parnell from the University of Aberdeen in Scotland embedded fossilized microbes into a fake meteorite strapped to the exterior of the Russian Foton M3 scientific-research probe, which went into orbit on Sept. 26 and came back to Earth 12 days later.
"In the bit of rock we got back, some biological compounds have survived," Parnell told National Geographic News.
The large number of rocks from Mars that end up on Earth lends credence to the hypothesis that terrestrial life may have had its origin on the Red Planet, which 4 billion years ago was much more hospitable than Earth was at the same time.
Alien Life Can Survive Trip to Earth, Space Test Shows
We could have alien origins, say scientists who sent fossilized microscopic life-forms into space and back inside an artificial meteorite.
The researchers attached the baseball-size rock to the outside of the European Space Agency's Foton M3 spacecraft to test whether biological material could survive the round-trip journey.
Sculpted from stone from the Orkney Islands in northern Scotland, the rock contained fossilized microbes and the molecular signatures of microbes.
The unmanned spacecraft was launched by rocket from Kazakhstan's Baikonur Cosmodrome carrying 43 experiments. The craft landed in Kazakhstan on September 26 after orbiting the planet for 12 days.
"In the bit of rock we got back, some biological compounds have survived," said project leader John Parnell from the University of Aberdeen in Scotland.
Preliminary findings suggest that it's possible simple organisms could arrive via meteorites, he said.
The research also suggests that living microbes would likely have survived in a slightly bigger rock, he added.
"This study of organic material is completely new," he said.
Previous artificial meteorite experiments have examined only the degree to which rocks melt upon entering the atmosphere.