The Earth Has Oceans And Continents: How Weird Is That? : 13.7: Cosmos And Culture : NPR
http://www.npr.org/...3.7/2017/03/07/518949218/the-earth-has-oceans-and-continents-how-weird-is-that
Seen from space, our planet has often been called a "blue marble."
It's not, however, just the swirly white clouds that give Earth its marbled appearance. The continents: They are
what complete the metaphor. All that land, sticking up above sea level, gives our world its distinctive look.
But now that we know the universe is awash in planets, just how distinct is our world? Is an almost equal mix of land and sea common — or will most planets
be either entirely desert or entirely ocean? Most importantly, how does the dry-land vs. open-water mix influence the evolution of intelligent life?
The relationship between land, water and the presence of intelligent observers (like us) is the topic of a provocative paper by Fergus Simpson, a researcher
at the University of Barcelona. One of the best things about Simpson's study is it reminds us of a simple fact about life on Earth: You can't take any of it
for granted.
Here is the thing: It is kind of weird that we live on a planet that has almost equal amounts of open ocean and dry land. Every planet will have some degree
of bumps on its surface — highland and lowlands. The more water the planet has, the more the lowlands get filled in. But if a planet doesn't have much in
the way of a water inventory, that world should be quasi-desert with nothing more than a bunch of disconnected lakes. This is exactly what is seen on Titan,
the giant moon of Saturn, which is the only other solar system body that shows liquid on its surface (of course Titan is so distant and cold that the lakes
are actually made of liquid methane at minus 292 degrees Fahrenheit).
But with enough water, sea levels will be above the highest point on the planet. In that case, what you have is an ocean world (astronomers prefer the term
water-world, sorry Kevin Costner). Getting the mix that Earth has, however, seems tricky. If our planet had just three times more water than it does now,
even Mt. Everest would be submerged.