Volcanic rock rafts could have played a key role in the origins of life on Earth, a team of scientists suggests.
Researchers say the buoyant rock pumice has the right properties to have provided the conditions for early life to emerge more than 3.5bn years ago.
Pumice "rafts" are found today on shores of islands such as the volcanic Greek island of Santorini (Thera).
The team, from Oxford University and the University of Western Australia, calls for more research on the idea.
"During its life cycle, pumice is potentially exposed to - among other things - lightning associated with volcanic eruptions, oily hydrocarbons and metals produced by hydrothermal vents, and ultraviolet light from the Sun as it floats on water," explained co-author Professor Martin Brasier from the University of Oxford.
"All these conditions have the potential to host, or even generate, the kind of chemical processes that we think created the first living cells."
The volcanic rock, as a result of its low density, floats on water and has the largest surface-area-to-volume ratio of any type of rock, which would have allowed it to act as a raft collecting material before becoming beached on a shore.
Another of the scientists involved, Dr David Wacey from the University of Western Australia, said that it was known that that life was "thriving" among beach sand grains some 3.4bn years ago.
"What we are saying here is that certain kinds of beach might have provided a cradle for life," he said.
The two researchers were part of an international team which recently published a paper suggesting that microscopic fossils unearthed in Western Australia provided "good, solid evidence" for cells and bacteria living in an oxygen-free world more than 3.4bn years ago.
Writing in their latest paper, to be published in the journal Astrobiology, the team said that the idea that rafts of pumice could have played a significant role in the emergence of some of the earliest organisms on Earth deserved to be "rigorously explored in the laboratory and the early rock record".