Most habitable planets likely to be waterworlds
It may be a case of water, water, everywhere among Earth-like planets beyond the solar system.
A new study suggests that most habitable planets are likely to be waterworlds with oceans spanning 90% of their surfaces.
The fine balance between land and sea found on Earth, which is 71% ocean covered, could be a key factor behind the emergence of advanced life, scientists believe.
Lead researcher Dr Fergus Simpson, from the Institute of Cosmos Sciences at the University of Barcelona, Spain, who used a statistical model to predict the division between land and water on habitable worlds, said: "A scenario in which the Earth holds less water than most other habitable planets would be consistent with results from simulations, and could help explain why some planets have been found to be a bit less dense than we expected."
For a planetary surface to support large areas of both land and sea requires a delicate balance to be struck between the volume of water it retains over time and how much storage space exists in its oceanic basins.
Why the balance is so good on Earth from the point of view of evolving life has been a long-standing mystery.
One explanation could be the so-called "anthropic principle", says Dr Simpson.
This refers to the idea that if the universe had not developed just the way it has, we would not be here to observe it.
In the realms of physics and cosmology, it could account for some apparently astounding coincidences.
Alter the mass of quarks - fundamental building blocks of matter - or the strength of gravity, electromagnetism, and the strong and weak forces that govern the binding and decay of atomic nuclei just a little, and a universe conducive to sentient life would not exist.
The fact that we are here at all means that all these precise values must have been set.
At a more down to Earth level, the unusual ratio of land and water found on our planet could be another example of fine tuning necessary for intelligence.
"Based on the Earth's ocean coverage of 71%, we find substantial evidence supporting the hypothesis that anthropic selection effects are at work," said Dr Simpson.
As part of the study, published in the journal Monthly Notices of the Royal Astronomical Society, Dr Simpson took into account feedback mechanisms such as the deep water cycle and erosion and deposition processes.
He also looked at the way planets with smaller oceans became increasingly dominated by uninhabitable deserts.
Dr Simpson added: "Our understanding of the development of life may be far from complete, but it is not so dire that we must adhere to the conventional approximation that all habitable planets have an equal chance of hosting intelligent life."