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Sock Munkey
2005-Jul-12, 10:19 AM
Hypothetically speaking if the sun were still burning by the time the Earth's internal heat had expended itself, would erosion wear the whole world smooth and fill in the oceans leaving the whole planet covered by a shallow ocean?

mickal555
2005-Jul-12, 10:59 AM
Hmmm I dunno

I wounder why mars isn't smooth though- although it hasn't had a great deal of time to do so and it has thinner atmosphere no water....

Eroica
2005-Jul-12, 11:51 AM
Hypothetically speaking if the sun were still burning by the time the Earth's internal heat had expended itself, would erosion wear the whole world smooth and fill in the oceans leaving the whole planet covered by a shallow ocean?
If plate tectonics have ceased, I don't see how any more mountain-building could take place ... so, yes, I'd say you're right. (Although I don't know that the ocean would necessarily be "shallow".)

Sock Munkey
2005-Jul-12, 07:17 PM
The average depth of the ocean would be reduced by 33% I imagine. Unless the free circulation of water let the ice caps melt... Hmm.
Then again, the increase in Earth's albedo from a worldwide ocean might cool it.
Ack, too many variables!

Eroica
2005-Jul-13, 11:25 AM
The average depth of the ocean would be reduced by 33% I imagine.
Yes, you're right.

Ocean Volume = 1.37e9 km≥
Earth's Surface Area = 5.096e8 km≤
=> Average Ocean Depth = 2.688383 km

That is indeed about a third less than the current value of about 4 km.

MAPNUT
2005-Jul-13, 06:45 PM
How's this for prognostication: Let's assume that the mantle cools and solidifies so that continental plates won't subside from their own weight as opposed to seafloor plates. Erosion of land areas will continue but as the land elevations decrease, the gradient from high ground to the ocean flattens and the rate of erosion decreases. When the last mountains are ground down, the runoff will hit flat ground immediately and the sediments will be deposited. Rivers, having very flat gradients, will meander all over the place and lose their ability to carry sediments to the sea. By this time continents will have grown in area somewhat, from deposition in deltas and on continental shelves, but they can't grow much beyond the continental shelves. So at this point we have all flat continents maybe 10% larger than the present area, no more than a thousand feet above sea level. Water will get to the ocean only by percolation. At this point the only form of erosion will be wave erosion of the coasts, and this will reduce the areas of continents. But eventually the seacoasts below the water line will become so flat from sand deposition that waves can no longer arrive at the shore with sufficient energy to erode. We will have an equilibrium with flat, flat continents about 10% less than the present area, all of which end in cliffs at the shore, below which are flat, flat beaches with no surf.

All of this is complete layman's **. Who would like to take on the role of corals? Glaciers?

Sock Munkey
2005-Jul-14, 04:47 AM
Hmm pretty cool, but if the caps melted as I suspect they would the landmass would be even smaller.
Anyhow, if this were combined with my other notion about he Earth becoming tidally locked to the moon we would have one freaky environment.

Eroica
2005-Jul-14, 07:57 AM
At this point the only form of erosion will be wave erosion of the coasts ...
There will still be weathering by wind and by changes in temperature.

Captain Kidd
2005-Jul-14, 11:06 AM
Hmm, this calls to mind a book I read... can't remember the title or by who, but it was fairly old... 70's, or earlier maybe, I think was the last copyright date.

A submarine somehow travels to the future. The land masses had become close to what MAPNUT prognosticated. As far as the crew could see the land was barely above sea level and a murky grey color with no vegetation. I think weather had basically stalled out and the ocean was extremely calm. The author kinda took the erosion factor a bit far and when they dispatched a landing craft, the first couple guys to jump out immediately sank as the land was barely denser than the ocean. (Which leads to the question of why, even without weather, it didn't settle out over the seabed... maybe it was in the process of doing that.)

tofu
2005-Jul-14, 12:16 PM
A large amount of sea-water seeps into the crust every year and is lost. Fortunately, the mantle is full of various gasses, so when a volcano erupts some of what's lost is put back. Long before the Earth finishes cooling though, volcanism will cease and that balance will be lost. The seas will slowly wither away and the atmosphere will slowly be lost to space. At some point, the pressure will be too low for liquid water, leaving only wind erosion. This is basically what happened to Mars.

So I would guess that, long before the Earth could be eroded into a smooth sphere, all of the liquid water would disappear, and since wind erosion is much slower, I think the planet would be pretty stable for billions of years after that. Dead, but stable.

It's a good thing we have a big moon to push us around with tides and keep the planet's insides warm, isn't it?