But there are other factors to consider than how Earth got its water, such as how the ocean's depths are regulated by interactions between the deep ocean and Earth's mantle. For example, Earth may be unique in that it features unusually deep water basins. More research will be required to determine if this is the case.
Simpson himself factored in some of these effects, and had his test model account for the deep water cycle, erosion, and deposition processes (i.e. the process in which sediments, soil, and rocks are added to a land mass). Despite this, he still found that water is be a prevailing surface feature in most cases. Interestingly, he found that planets with small oceans feature land masses dominated by deserts. Also, large Earth-like planets are almost guaranteed to be waterworlds.
"Larger planets are thought to be more prone to flooding for two reasons," Simpson told Gizmodo. "One is that if they have the same composition (percentage of water by mass) then their oceans are deeper. The second is that their higher surface gravity makes it harder to have such large surface perturbations [dynamic topological features]."
If Simpson's conclusions are valid, then it means our planet has struck a fine balance between land and ocean-an observation that may help to explain why our civilization emerged on Earth (despite what some might say, it is highly unlikely that a high-tech, industrial-scale civilization can develop on a world consumed by water). And in fact, Simpson says that anthropic selection effects are at work. That's a fancy way of saying that Earth is a freaky planet, because if it wasn't freaky, we wouldn't be here to see it.
The trouble with the
Anthropic Principle, of course, is that it's untestable. But thankfully, this new waterworld theory is.
"The exciting aspect is that we may not be too far from measuring the atmospheric composition of terrestrial exoplanets," said Simpson. Indeed, with the next generation of telescopes, including those situated in space, we'll be able to scan the atmospheres of exoplanets to determine how much water might be on the surface.
In addition, scientists will need to figure out the various ways in which our planet is an oddball, and why. Until then, let's celebrate the fact that Earth is a weirdo of the Milky Way.
Monthly Notices of the Royal Astronomical Society]