I’m not sure it’s possible for the earth to be covered with water in the either the hard or soft state. As ice builds up on the land sea levels will lower exposing more land. As long as weather still produces wind large areas of land are likely to be exposed also. Perhaps the opposite condition of being much hotter would cover the entire surface of the earth in water vapor. Luckily we live in the Goldilocks climate where most of the water is in the oceans and some land, at least for a while, is covered in ice.
Earth can’t be completely covered with water … given the current topography and current supply of water. If it could, it would be.
A magic wand could add enough water to drown all the land or could flatten the highlands and raise the lowlands (seafloors actually) enough that the current supply of water covered everything. As cited above, to a depth of some 8,800 feet or roughly 1.7 miles. It’s not like there’s just barely enough water to go around.
If we imagine a future Earth where tectonics & vulcanism has slowed enough that mountains are no longer being uplifted, eventually they’ll be weathered away as silt into the lowlands. Which will have the effect of displacing seawater upwards. After a long, long, long asymptotic process the Earth will become a water planet.
I don’t see ice caps on land as having a definitive influence on the eventual outcome. And of course sea ice has no effect whatsoever.
Continental rock is slightly lighter than oceanic basin rock and so the continents “float” on the underlying denser rock. Some believe that it took ages for geologic processes to form the continental rock and so early earth may have been largely ocean covered:
Earth may have been a 'water world' 3bn years ago, scientists find | Science | The Guardian
This actually makes a lot of sense to me as it would suggest a phase that is currently in a sweet spot. If we had 20% more water or 20% less water i doubt life on earth as we know it could exist. Hard to imagine something that needs to be so specific being permanent.
The sun is getting brighter, verrrry slowly, all the time. I’m pretty sure by the time plate tectonics and mountain-building ceases, liquid water won’t be able to exist on Earth’s surface anymore. The atmosphere with all that water vapor might have been blown away too.
The loss of liquid water might cause the mountain and continent-building to cease right after that, though. This video explains why we have basically 2 different main levels in the Earth’s crust, 3 minutes:
TL;DW: the water that gets subducted from plate tectonics is incorporated into rock that winds up lighter in density, thus building up the continents that float on denser rock.
Yeah for sure if we include the Sun brightening then the far future Earth never gets water covered. I was trying to describe th econsequences of changing just one parameter, not all of them.
This explains a regulating factor to surface areas covered by water.
Hmm, I just rewatched the video, and that one didn’t include the bit about why continental crust is less dense. I thought I’d learned it there, but it was probably some other video from that channel or some other educational channel like Be Smart, Sci-show or Crash Course.
The wiki on
is pretty good.
The reason continental crust is lighter than oceanic crust has to do with which minerals it contains. Not because it’s full of water. Abundant surface water does have some role in plate tectonics, mostly by lubricating subduction.
Water has completely covered the whole Earth in the past.
By my rough calculation it would take about three times as much water as we have now to create an ocean world.
(The Earth is a sphere of radius 6,371,000 meters, and Mount Everest has a height of 8,900 meters, so it would require a shell of volume 4.55 x 10^18 m cubed of water to go from sea level to the top of the Himalayas. Current volume of the Earth’s oceans is 1.4 x 10^18 m cubed. Ignoring the icecaps, the compression of the land, the tides, the leaky pipe in my basement, etc.)
How much would it take for a 4000 meter rise?
2.0 x 10^18 meters cubed of extra water would be needed, so as much as in the oceans now, plus about as much coffee as I drink in a week.
YouTube of the Earth with sea level rises from 0 to 9000 meters: https://www.youtube.com/watch?v=UnMHuZVPUeE
It’s something to hope for…