Geology: How does a cooling planet move continents

[stitt29]

Hi,

Just wondering how a cooling planet can move continents and build mountains. I feel there must be a heat source to keep up the internal pressure to enable all this. The Heat source could be the sinking of dense magma from the top of the mantle once it has cooled.

I looked up the mass of the crust which came to 2% of the Earth's mass, which is about 1.2 x 10^22kg. The energy required to move this over billions of years must be considerable. Is there any measurement of magma cooling over the centuries that would indicate the Earth's interior is actualy cooling.

It seems more likely that the earth has a heat source which keeps up the internal pressure. The pressure is released when volcanoes erupt and Ocean floors spread. The only way to restore the pressure must be from a heat source. Any thoughts Geologists

[cope]

Well, the planet is cooling or losing heat. That heat is moving from the Earth's interior to its surface. This heat is transferred by the process of convection, the motion of a fluid in response to differences in temperature/density.

However, the process is complicated by the fact that there is a continuous source of heat in the Earth's interior which is the decay of radioactive materials.

The suggestion has been made that there may be atomic fission happening in the core as well which further complicates matters should that turn out to be true.

[jlhredshift]

Hi,

Any thoughts Geologists

Hello, I am not a Geologist, but to quote me:


Originally Posted by jlhredshift
I would point out however, that the continents are, in essence floating on a sea of plastic material that itself is floating on a viscous liquid and it is not so much that they are shoved around as it is that they are along for the ride as the different density materials that are irregularly distributed seek equilibrium in a highly dynamic system that is affected by tidal gravitation, the Coriolis force, heat input from radioactive decay, and heat outflow to the universe.

My bold.

This is the biggest source of new energy by far and Earth still has a lot of the old. Rock is a good insulator. The Earth is big enough, and its size is key, and was granted enough radioactive material that it is still viscous in its interior at this time during our presence. The planet has not achieved equilibrium and from an entropic point of view, it is cooling. The planet does not operate on Human timescales and the local variabilities, in the larger sense, have no specific relation to its evolution in geologic time, what is known as "Deep Time".

[jlhredshift]

From The Deep and the Past by Ericson and Wollin; 1964, pg 273:


In the meantime, what has become of the supposedly irrefutable objections to continental drift? In the light of the new dynamic conception of the nature of the ocean basins, they vanish into thin air. It is not the continents which had to plow through the resistant rocks of the ocean floor, impelled by some gratuitous force; it is the "resistant" rocks themselves which are moving, or flowing, as convection currents powered by radioactive heating. The whole thing is explicable in terms of well-known processes. On this mobile setting, drift of the continents becomes inevitable.

I chose this reference because it was written, by two oceanographers, at the time of the beginning of the Plate Tectonic revolution.

I would refer any interested party to Naomi Oreskes book, Plate Tectonics.

[stitt29]

Even if it is true that the Earth is heating because of radioactive decay, the heat from radioactive decay would decrease over time. This would be measurable as the magma would get cooler. Does anyone have evidence that Magma below the crust is cooling. I also find it quite hard to believe that radioactive decay could build the Himalayas or push South America thousands of miles from Africa.

How much radioactive decay would be required to melt one tonne of rock? Is there even enough to do this? The radioactive decay needed to keep the mantle molten would be enormous we're talking about thousands of billions of billions of tonnes. It doesn't seem feasible are there any figures on this?

[jlhredshift]

Even if it is true that the Earth is heating because of radioactive decay, the heat from radioactive decay would decrease over time. This would be measurable as the magma would get cooler. Does anyone have evidence that Magma below the crust is cooling. I also find it quite hard to believe that radioactive decay could build the Himalayas or push South America thousands of miles from Africa.

How much radioactive decay would be required to melt one tonne of rock? Is there even enough to do this? The radioactive decay needed to keep the mantle molten would be enormous we're talking about thousands of billions of billions of tonnes. It doesn't seem feasible are there any figures on this?

My bold.

That, my friend, is the right question. The only quibble I would have is the term "molten", I would prefer either viscous or plastic. If it did not flow would we have a magnetic field; is the next "right" question.

Another wondrous thing is that the uplift of the Himalayas occurred recently, during the Pliocene and the Pleistocene. J. D. Dana (http://en.wikipedia.org/wiki/James_Dwight_Dana) and E. Suess (http://en.wikipedia.org/wiki/Eduard_Suess)both proposed a contracting Earth in the late nineteenth century for an explanation of these events followed by S. W. Cary proposing an expanding Earth in the fifties. But, by the seventies the work of Vine, Matthew, and Morley (http://en.wikipedia.org/wiki/Morley-Vine-Matthews_hypothesis) led the way to Plate tectonics. I would also refer you to the work of Jason Morgan and X. Le Pichon.

You can search for number on the amount of heat generated, but all you will get is an order of magnitude, but that is sufficient because "yet, it moves". But, there is this:

First measurements of Earth's core radioactivity (http://www.newscientist.com/article/mg18725103.700) from the New Scientist 2005

[Delvo]

Even if it is true that the Earth is heating because of radioactive decayNot heating; cooling at a slower rate than it would otherwise. One early geologist actually calculated how rapidly the world would have cooled off using ordinary thermodynamics and determined that it was much younger than we now believe (in the millions of years instead of billions) because he didn't know about radioactive decay. (Nobody did back then.)


the heat from radioactive decay would decrease over time.I'm not sure. If the planet's insulating ability is great enough, meaning its ability to transmit heat out efficiently is weak enough, then the limiting factor could be not the rate of generation of new heat but the rate at which it passes up to our level and beyond. In that case, there'd be little or no change in temperature perceivable from here; the constant rate of heat transfer would look like equilibrium, and any more or less heat generated in the core would just sit trapped in there until long after it's generated.


This would be measurable as the magma would get cooler. Does anyone have evidence that Magma below the crust is coolingWithin the span of human history, no. It's going much more slowly than that, so the evidence would only appear as rock formations that seemed to have been formed under different conditions millions of years apart. I don't know the details of what that evidence is, but I do know that mainstream geologists believe there are reliable indicators of past eras'/epochs'/periods'/ages' temperatures, and that they have established a timeline of the Earth's temperature since its beginning. A textbook from a geology class I took in college in 1995 or 1996 had a graph of this. It's steep at the left and nearly flat at the right with a curved concavity between, somewhat like hyperbolas, indicating a rapid cooling rate at first and a drastic slowdown in cooling since then to a rate so low that it appears practically the same as no change at all over the last several hundred million years (at least). At this rate, the time it would take to reach equilibrium with space would be well into the billions of years into the future, and changes in the sun will interrupt before that much time passes.

[geonuc]

I also find it quite hard to believe that radioactive decay could build the Himalayas or push South America thousands of miles from Africa.
As pointed out, don't forget that the earth retains a lot of the heat from its formation.

[jlhredshift]

Not heating; cooling at a slower rate than it would otherwise. One early geologist actually calculated how rapidly the world would have cooled off using ordinary thermodynamics and determined that it was much younger than we now believe (in the millions of years instead of billions) because he didn't know about radioactive decay. (Nobody did back then.)

That would be Lord Kelvin and he was a physicist.


I'm not sure. If the planet's insulating ability is great enough, meaning its ability to transmit heat out efficiently is weak enough, then the limiting factor could be not the rate of generation of new heat but the rate at which it passes up to our level and beyond. In that case, there'd be little or no change in temperature perceivable from here; the constant rate of heat transfer would look like equilibrium, and any more or less heat generated in the core would just sit trapped in there until long after it's generated.

This is where the size of the Earth is important. If it had been as small as Mars tectonics probably would have ceased by now. Volume goes as the cube, surface area goes as the square; this slows cooling.


Within the span of human history, no. It's going much more slowly than that, so the evidence would only appear as rock formations that seemed to have been formed under different conditions millions of years apart. I don't know the details of what that evidence is, but I do know that mainstream geologists believe there are reliable indicators of past eras'/epochs'/periods'/ages' temperatures, and that they have established a timeline of the Earth's temperature since its beginning. A textbook from a geology class I took in college in 1995 or 1996 had a graph of this. It's steep at the left and nearly flat at the right with a curved concavity between, somewhat like hyperbolas, indicating a rapid cooling rate at first and a drastic slowdown in cooling since then to a rate so low that it appears practically the same as no change at all over the last several hundred million years (at least). At this rate, the time it would take to reach equilibrium with space would be well into the billions of years into the future, and changes in the sun will interrupt before that much time passes.

Yeah, we have some time left.

[jlhredshift]

Originally Posted by stitt29
I also find it quite hard to believe that radioactive decay could build the Himalayas or push South America thousands of miles from Africa.


As pointed out, don't forget that the earth retains a lot of the heat from its formation.

correct

It is not a push it is a slab pull (http://www.windows.ucar.edu/tour/link=/earth/interior/how_plates_move.html)to be technical.

[geonuc]

It is not a push it is a slab pull (http://www.windows.ucar.edu/tour/link=/earth/interior/how_plates_move.html)to be technical.
I think that's not settled yet? Even the link you provide mentions both slab pull and ridge push.

[jlhredshift]

I think that's not settled yet? Even the link you provide mentions both slab pull and ridge push.

I'm OK with not totally settled yet, it just makes sense to me that slab pull is the instigator, but there is always more to learn and I am open to it.

Edit to add: When I look at the transform faults normal to the Mid-Atlantic Ridge, I have a hard time conceiving that pushing is the operative mechanism.

[korjik]

Another source of free energy is heat released when the outer core crystalizes.

Stitt29, there is some indirect evidence that the earth is cooling. Looking at the ages of the individual bits of continents shows that the amount of continental crust has been slowly increasing over time. The thought is that the increased heat of the Earth prevented continents from forming early on.

[captain swoop]

Don't forget Friction. Heat gets recycled by Subduction.

[stitt29]

QUOTE]Stitt29, there is some indirect evidence that the earth is cooling. Looking at the ages of the individual bits of continents shows that the amount of continental crust has been slowly increasing over time. The thought is that the increased heat of the Earth prevented continents from forming early on.
[/QUOTE]
But isn't there more evidence that the Earth is heating(cooling at the surface but heating in the interior). The earth radiates energy, Gas Giants radiate more energy, and stars even more still.

Don't forget Friction. Heat gets recycled by Subduction.
And isn't this the reason they all radiate more energy the more we go up in scale i.e. Subduction of cooler matter generates heat. It won't happen with a pot of water but on these giant scales subduction must generate heat.

[Hornblower]

Stitt29, there is some indirect evidence that the earth is cooling. Looking at the ages of the individual bits of continents shows that the amount of continental crust has been slowly increasing over time. The thought is that the increased heat of the Earth prevented continents from forming early on.

But isn't there more evidence that the Earth is heating(cooling at the surface but heating in the interior). The earth radiates energy, Gas Giants radiate more energy, and stars even more still.

And isn't this the reason they all radiate more energy the more we go up in scale i.e. Subduction of cooler matter generates heat. It won't happen with a pot of water but on these giant scales subduction must generate heat.

You appear to be losing some basic physics in the clutter of complications in real planets.

Our planet can be cooler inside now than a billion years ago, and still be plenty hot for volcanic activity and plate tectonics. Those activities may well have been more vigorous back then, and we can expect them to gradually become less vigorous as the planet continues to cool down and eventually freezes up over many billions of years in the future. That is assuming it does not get incinerated when the Sun flares up in its dying gasp.

As an analogy, take a red hot piece of iron out of a forge and let it stand for a few minutes. The glow will fade, but the iron can still be plenty hot to boil a drop of water or burn your fingers.

For a planet that was similarly hot when formed, that cooldown takes billions of years rather than a few minutes, for reasons already discussed in this thread and elsewhere.

Let me add that the half-life of uranium or thorium is about the same order of magnitude as the cooldown rate of an Earth-sized planet would be in the absence of those radioactive substances.

[stitt29]

Our planet can be cooler inside now than a billion years ago, and still be plenty hot for volcanic activity and plate tectonics.
I do not disagree that what you are claiming is not possible(sort of)-The Earth is cooling- but what I'm saying is also possible and much more likely- the Earth is heating.

Those activities may well have been more vigorous back then, and we can expect them to gradually become less vigorous as the planet continues to cool down and eventually freezes up over many billions of years in the future.

if we are cooling we could still get tectonic activity but why would the youngest Mountain range be the highest, this could only happen if the Earth was heating overall. In a cooling Earth the oldest mountain ranges would be the tallest the newer ones would be smaller.

Let me add that the half-life of uranium or thorium is about the same order of magnitude as the cooldown rate of an Earth-sized planet would be in the absence of those radioactive substances.

How many tonnes or kg. of Uranium or thorium would be equivalent to the Earth's cooldown rate without these substances. And what is that rate?
Also when lava flows from a volcanoe is it measured as very radioactive? i.e proving that the interior is so radioactive it is heating the mantle.

[geonuc]

if we are cooling we could still get tectonic activity but why would the youngest Mountain range be the highest, this could only happen if the Earth was heating overall. In a cooling Earth the oldest mountain ranges would be the tallest the newer ones would be smaller.
No. The Himalaya is the highest partly because it is a young range. It is still rising. Older ranges which are no longer under tectonic stress and are no longer rising have eroded with time. For example, the Appalachians used to be huge, but now they are merely big hills.

[geonuc]

I do not disagree that what you are claiming is not possible(sort of)-The Earth is cooling- but what I'm saying is also possible and much more likely- the Earth is heating.
Much more likely? I'd say you need to back that up with some reasoning and probably move this discussion to ATM.

[jlhredshift]

I do not disagree that what you are claiming is not possible(sort of)-The Earth is cooling- but what I'm saying is also possible and much more likely- the Earth is heating.

if we are cooling we could still get tectonic activity but why would the youngest Mountain range be the highest, this could only happen if the Earth was heating overall. In a cooling Earth the oldest mountain ranges would be the tallest the newer ones would be smaller.

How many tonnes or kg. of Uranium or thorium would be equivalent to the Earth's cooldown rate without these substances. And what is that rate?
Also when lava flows from a volcanoe is it measured as very radioactive? i.e proving that the interior is so radioactive it is heating the mantle.

The oldest mountains have experienced the most time for the ravages of erosion to reduce them to sea level, eventually; deep time again.

The lava is the melt from heat that has arisen from below, not direct material from the core; your pan example. It might be helpful if I knew what region of the world in which you live and I might possibly be able to point to examples that are close to you.

[stitt29]

So far we had the Earth is cooling, but this has been changed to having a heat source of radiation, which is undetectable, as it is in the core. But still cooling

A cooling Earth will reduce it's activity but the highest mountain ranges are the newest. The older mountain ranges are smaller due to erosion, the Appalachians are now small at 1000m to 1500m. Were they ever above 10,000m? They couldn't have eroded from bigger than the Himalayas to what they are now, surely. And all the other mountain ranges that are smaller than the Himalayas they were also bigger but have eroded into hills?

It is much more likely that the Earth is heating, thus building the highest mountain range it has ever had. The older mountain ranges could have been 3000m and eroded, then 4000m and eroded etc, which indicates increasing tectonic activity and not decreasing.

I'm in Scotland

[Gillianren]

The older mountain ranges are smaller due to erosion, the Appalachians are now small at 1000m to 1500m. Were they ever above 10,000m? They couldn't have eroded from bigger than the Himalayas to what they are now, surely. And all the other mountain ranges that are smaller than the Himalayas they were also bigger but have eroded into hills?

Well, your first error is that the highest peak in the Appalachians is over 2000m. So there's that.

Your second error is that, in fact yes, they were that tall just a couple hundred million years ago. So there's that as well.

Look, I grew up in the foothills of the San Gabriel Mountains in Los Angeles, California. The San Gabriels are falling down as fast as they're being built up because of a combination of geological stresses and erosion. (To be a little more specific, the geological stresses cause erosion, inasmuch as they break the bedrock into easier-to-fall pieces.) They were never as high as the Himalayas; there's no requirement that they had to have been. But I learned in my college geology class that, were they not, as stated, falling down a lot, they'd be the fastest-growing mountain range in the world; there's an argument, of course, that they are anyway.

[geonuc]

So far we had the Earth is cooling, but this has been changed to having a heat source of radiation, which is undetectable, as it is in the core. But still cooling No, we've always maintained the earth is cooling. The presence of radioactivity in the mantle/core merely slows the rate of cooling from what it would be otherwise.


A cooling Earth will reduce it's activity but the highest mountain ranges are the newest. The older mountain ranges are smaller due to erosion, the Appalachians are now small at 1000m to 1500m. Were they ever above 10,000m? They couldn't have eroded from bigger than the Himalayas to what they are now, surely. And all the other mountain ranges that are smaller than the Himalayas they were also bigger but have eroded into hills?Plenty of misconceptions here. Yes, I believe the Appalachians rivaled the height of the Himalaya, if they weren't bigger. As Gillian said, they are still higher than 1500 meters in places.

Why couldn't the Appalachians have eroded down this far in 200-odd million years? How long do you think it should take?

As to 'all the other mountain ranges', what are you suggesting? That because the present-day Himalaya is a high range that it must be the biggest ever? How do you support that conclusion?


It is much more likely that the Earth is heating, thus building the highest mountain range it has ever had. The older mountain ranges could have been 3000m and eroded, then 4000m and eroded etc, which indicates increasing tectonic activity and not decreasing.Again with the 'much more likely'. Why? As to the 3000, 4000m meter statement, you're just making stuff up. What do you know about the historical tectonic record?

[Amber Robot]

There seems to be a fundamental misunderstanding here that you've repeated several times. Whether an object is cooling or heating up is a matter of balance between heat generation and heat loss. If the loss is greater than the generation then it will cool. So, you can have an object that has both a heat source as well as be cooling.

[stitt29]

Well, your first error is that the highest peak in the Appalachians is over 2000m. So there's that.
thanks for that correction. misread wikipedia, they are 900m on average, highest mount Mitchell at 2037m.

Your second error is that, in fact yes, they were that tall just a couple hundred million years ago. So there's that as well.
Is this true, that these mountains were over 10000m 2hundred million years ago now down to 2037m at highest. Whose theory is this? Any other examples of higher mountains than the Himalayas reduced down to 2000m?

Still looks like a heating planet to me, not a cooling one

[geonuc]

Still looks like a heating planet to me, not a cooling one
OK, good argument.

[Amber Robot]

Still looks like a heating planet to me, not a cooling one

All you have is an argument for a warm planet. You need more information to determine whether it is cooling or heating.

[stitt29]

Again with the 'much more likely'. Why? As to the 3000, 4000m meter statement, you're just making stuff up. What do you know about the historical tectonic record?
Reply With Quote
nothing can you tell me where the mountain ranges are that were bigger than the Himalayas? Also as fish fossils are found at the top of mountains, this suggests that the Earth was originally flatter and has been been getting more mountainous over time.


Plenty of misconceptions here. Yes, I believe the Appalachians rivaled the height of the Himalaya, if they weren't bigger.
What evidence is there for this belief?

Also I know everyone has always maintained there is a heat source but we are cooling overall. I am suggesting, because it seems more logical and fits observation better, that we have a heat source but are still getting hotter over time(even though we are radiating heat).

[geonuc]

nothing can you tell me where the mountain ranges are that were bigger than the Himalayas? Also as fish fossils are found at the top of mountains, this suggests that the Earth was originally flatter and has been been getting more mountainous over time.I don't know off-hand. It may be that the Appalachians are the largest eroded range we can accurately describe from a historical perspective. Perhaps their counterparts in Europe and Africa were as large.

The presence of fossils at the top of mountains suggests no such thing, at least to anyone who knows how mountains are formed during orogenies. Do you? The top of Everest is marine limestone. Do you know how that came to be?

The earth as a whole may indeed be getting more mountainous over time, but, if so, it isn't because tectonic activity is increasing due to a hotter core, it is because the areal extent of the continents is growing.


What evidence is there for this belief?The sediment load on the east coast of North America.


Also I know everyone has always maintained there is a heat source but we are cooling overall. I am suggesting, because it seems more logical and fits observation better, that we have a heat source but are still getting hotter over time(even though we are radiating heat).Can you see that your 'observations' are not grounded in solid geological science?

[hhEb09'1]

How much radioactive decay would be required to melt one tonne of rock? Is there even enough to do this? The radioactive decay needed to keep the mantle molten would be enormous we're talking about thousands of billions of billions of tonnes. It doesn't seem feasible are there any figures on this?

My bold.

That, my friend, is the right question. The only quibble I would have is the term "molten", I would prefer either viscous or plastic. If it did not flow would we have a magnetic field; is the next "right" question.If the mantle did not flow, we'd still have a magnetic field because it is generated in the core of the Earth, not the mantle.
But, by the seventies the work of Vine, Matthew, and Morley (http://en.wikipedia.org/wiki/Morley-Vine-Matthews_hypothesis) led the way to Plate tectonics. I would also refer you to the work of Jason Morgan and X. Le Pichon.Just a nit, but plate tectonics arose (via Jason Morgan et al) in the sixties.



A cooling Earth will reduce it's activity but the highest mountain ranges are the newest. The older mountain ranges are smaller due to erosion, the Appalachians are now small at 1000m to 1500m. Were they ever above 10,000m? They couldn't have eroded from bigger than the Himalayas to what they are now, surely.Probably a bad example, because I think the current height of the Appalachians is from fairly recent uplift--but of uplift of remnants of older mountain ranges. But there have seemed to have been some big mountains in the past. The Himalayas are the result of continental-continental collision, which wasn't so likely in the past.
It is much more likely that the Earth is heating, thus building the highest mountain range it has ever had. Not necessarily. If you want to pursue this idea, go ahead and open up a thread in ATM. You might want to look into it more first, and have your argument in order.

[stitt29]

Quote:
Originally Posted by stitt29 View Post
Still looks like a heating planet to me, not a cooling one
All you have is an argument for a warm planet. You need more information to determine whether it is cooling or heating.
Reply With Quote
no one offers any evidence for it cooling, I have put forth loads that it is heating. Only a heating planet would have increasing internal pressure that would power mountain building. Decreasing internal pressure would not enable this.
If the Appalachions were bigger than the Himalayas at one time, the distances between peaks would be greater than those in the Himalayas. Does anyone know if this is the case?

[geonuc]

The Himalayas are the result of continental-continental collision, which wasn't so likely in the past.
The Appalachians resulted from cont-cont collisions, as well (e.g., Allegheny Orogeny).

[geonuc]

no one offers any evidence for it cooling, I have put forth loads that it is heating. Only a heating planet would have increasing internal pressure that would power mountain building. Decreasing internal pressure would not enable this.What is this increasing internal pressure you refer to?

All the so-called 'evidence' you've put forward has just been your misunderstanding of how mountains are created.

If the Appalachions were bigger than the Himalayas at one time, the distances between peaks would be greater than those in the Himalayas. Does anyone know if this is the case?What does the peak-to-peak distances have to do with anything?

[cope]

They couldn't have eroded from bigger than the Himalayas to what they are now, surely.

Ah Scotland, the birthplace of geology. I was lucky enough to spend four summers studying field geology there. The most important lessons I learned were that deep time is VERY, VERY DEEP and, therefore, much of geology involves inferential evidence.

Per the ultimate height of the Appalachians, from this article (http://www.main.nc.us/sams/blueridge.html) comes this quotation: " Based on the tremendous volume of material eroded from them and deposited along the east coast of the United States, it is estimated that a layer of rock as much as 20 miles in thickness has been removed."

Assuming that the Appalachian mountains had a tectonic root as deep as they were high gives an ultimate height greater than the present Himalayan mountain chain.

As to the question of whether the Earth is cooling or heating, given that the sources of internal heat (remnant and radioactivity) are finite, then in the grand scheme of things, the Earth is cooling. It is not accumulating additional heat sources through time from any outside source. One can only say the Earth is heating up if it is absorbing heat energy from an external heat source.

Heat energy flows from hot things to cooler things. Since heat is flowing away from the Earth, it is cooling.

[cran]

no one offers any evidence for it cooling,

the hottest modern lavas are basaltic (mafic), and average ~1150 deg C at surface ...
the hotter Archaean lavas were komatiitic (ultramafic), and had to have erupted at 1400 deg C or more (the temperature required to form those mineral associations and produce the flow patterns found) ...

some mineral and metal associations only form at specific pressure and temperature ranges (eg chrome-nickel-PGEs); we can map the in-situ deposits (and distinguish from the transported deposits), determine the formation ages of the host rocks (using both relative and radiometric methods), and correlate the mineral formation properties against time ...
guess what? higher temperature mineral formations are consistently older than lower temperature formations ...



I have put forth loads that it is heating. Only a heating planet would have increasing internal pressure that would power mountain building.Rubbish ...
put yourself into a large carton with a portable fan heater, and turn it on ...
have someone else lower you and the carton into a deep pit and then backfill the pit with rocks ...
which would you feel more pressure from?


Decreasing internal pressure would not enable this. no one has claimed decreasing internal pressure ...

when rocks cool, their density increases, and
pressure lost via outgassing and surface eruptions is offset by increasing overburden ...
similar results happen at surface (eg, cooling seamounts, basin subsidence)


If the Appalachions were bigger than the Himalayas at one time, the distances between peaks would be greater than those in the Himalayas. Does anyone know if this is the case?
no one has claimed the Appalachians were bigger than the Himalayas, either ...
well, OK, someone has ...

vertical displacement (uplift) and erosion occur concurrently - 20 vertical km of erosion does not mean that the mountains attained 20 km height above surface at any time ...

as for heat sources, if you want to see what tidal forcing can do to a body's internal temperature, look up Io ...

[geonuc]

no one has claimed the Appalachians were bigger than the Himalayas, either ...
well, OK, someone has ...

vertical displacement (uplift) and erosion occur concurrently - 20 vertical km of erosion does not mean that the mountains attained 20 km height above surface at any time ...
That was me, and it's a fairly common notion. The sediment load on the eastern seaboard here is so huge that the Appalachians must have been quite high, even given multiple collision episodes.

[cran]

That was me, and it's a fairly common notion. The sediment load on the eastern seaboard here is so huge that the Appalachians must have been quite high, even given multiple collision episodes.

Well, we've touched on Appalachian evolution, multiple uplifts, concurrent uplift and erosion, etc, in other discussions (you were there - I saw you!) ...

as long as growth and uplift exceed erosion and mass wasting, expect increasing relative height - there is a modern theoretical limit, but I don't recall what it is ...

features like slope gradients and distances between peaks are affected by a whole bunch of factors, including the structural properties of the rock types involved, the age, rate and type of mountain-building involved, and the duration, intensity and type of erosion(s) involved ...

[cran]

Heat energy flows from hot things to cooler things. Since heat is flowing away from the Earth, it is cooling.

You might want to re-think this - heat flowing away from the Earth means that the Earth is hotter than its surroundings; likewise the outward heat flux within the Earth means that the deeper layers are hotter than the shallower layers, regardless of the absolute trend to lower internal temperatures ...

in simple terms, heat flow from the Sun doesn't mean the Sun is cooling, does it?

[cran]

So far we had the Earth is cooling, but this has been changed to having a heat source of radiation, which is undetectable, as it is in the core. But still cooling
not just in the core ... and not undetectable ...


A cooling Earth will reduce it's activity but the highest mountain ranges are the newest. The older mountain ranges are smaller due to erosion, the Appalachians are now small at 1000m to 1500m. Were they ever above 10,000m? They couldn't have eroded from bigger than the Himalayas to what they are now, surely. And all the other mountain ranges that are smaller than the Himalayas they were also bigger but have eroded into hills?

It is much more likely that the Earth is heating, thus building the highest mountain range it has ever had. The older mountain ranges could have been 3000m and eroded, then 4000m and eroded etc, which indicates increasing tectonic activity and not decreasing.Actually, it's because the Earth is cooler, but still active, that it can build the highest mountain range it has ever had ... the cooler asthenosphere and overlying rocks can support greater loads against gravitational slumping ...

simple experiment - build a cone out of hot wax, then build a cone out of cold wax; which is taller?

again, it's also because tectonic activity has decreased over time (though still a long way from stopping altogether) that large scale features can endure for longer ...

simple expirement - build a damp sandcone on a sheet of masonry and shake it a lot, then build it again and shake it a little; which lasts longer?

In anthropomorphic terms, the Earth is mature but not quite middle-aged (think early to mid- forties) ...

ETA: it takes less energy to maintain a given temperature in a material object than is required to increase that temperature ...

[Delvo]

as long as growth and uplift exceed erosion and mass wasting, expect increasing relative heightWhat is "mass wasting"?


If the Appalachions were bigger than the Himalayas at one time, the distances between peaks would be greater than those in the Himalayas. Does anyone know if this is the case?
features like slope gradients and distances between peaks are affected by a whole bunch of factors, including the structural properties of the rock types involved, the age, rate and type of mountain-building involved, and the duration, intensity and type of erosion(s) involved ...Stitt29's comment on this (although irrelevant because the size of any mountain range has nothing to do with the planet's cooling rate or alleged heating rate, and the planet has multiple mountain ranges of different sizes growing and shrinking at any given time) does raise an interesting point which nobody's answered yet: if features like the Appalachians come from the erosion of previously taller mountains more like the Rockies, Alps, or Himalayas, then what about the distance between peaks? In a big mountain range, peaks tend to be a few miles apart, horizontally, because they're miles tall. If each peak in such a range simply shrinks to a lower height due to erosion, then by the time they were only several hundred to a few thousand feet tall, you'd get shorter peaks which were still a few miles apart. But you don't. In the Appalachian highlands, you get peaks and ridges well under a mile apart, sometimes as little as a few hundred yards. Clearly this can't mean that these close-together peaks were once much taller and still just as close together.

The part that Stitt29 is missing, in taking this as a sign that the Appalachian highlands are not eroded mountains, is that a single mountain doesn't shrivel down to a single hill later; erosion can split a single mountain into two or more. It's an uneven process that will hit some spots harder than others on the same slope, not a smooth, evenly distributed removal of a continuous layer throughout the mountain range.


Heat energy flows from hot things to cooler things. Since heat is flowing away from the Earth, it is cooling.
You might want to re-think this - heat flowing away from the Earth means that the Earth is hotter than its surroundings... in simple terms, heat flow from the Sun doesn't mean the Sun is cooling, does it?It means the sun is or would be cooling if it weren't also generating new heat that wasn't heat before (by fusion)... which is probably Stitt29's problem regarding Earth, because it also is generating new heat that wasn't heat before (by decay and possibly fission). The difference is simply whether the creation of new heat is greater or less than the loss of the heat that's already there. The missing detail is that it's possible to be creating new heat and still be cooling down if the rate of loss exceeds the rate of creation.

This is exactly what happens to your own body every single time its temperature goes down (which happens many times in your life, normally at least once a day due to your sleeping cycle, even if you never do much physical exertion, and that's ignoring things like returning to normal after you've had a fever). You are ALWAYS generating heat while you're alive, but the rates at which you do so, and at which it escapes from you into your environment, vary, so the temperature goes both up and down at different times.

[cope]

You might want to re-think this -

From Wikipedia (cope steps back to avoid blasts at Wikipedia as a source): "Cooling is the transfer of thermal energy via thermal radiation, heat conduction or convection. "

Just because the heat is being replenished, there is still a net loss of heat energy by the Earth of something like .075 watts/square meter.

I'm just saying...

[geonuc]

What is "mass wasting"?Landslides and the like.

[geonuc]

Well, we've touched on Appalachian evolution, multiple uplifts, concurrent uplift and erosion, etc, in other discussions (you were there - I saw you!) ...

as long as growth and uplift exceed erosion and mass wasting, expect increasing relative height - there is a modern theoretical limit, but I don't recall what it is ...

features like slope gradients and distances between peaks are affected by a whole bunch of factors, including the structural properties of the rock types involved, the age, rate and type of mountain-building involved, and the duration, intensity and type of erosion(s) involved ...
Yes, all that is relevant and correct. That said, geologists have concluded that the Appalachians were once as big as the Himalaya, or on that order.

[cran]

What is "mass wasting"?
mass wasting processes (http://earthsci.org/Flooding/unit3/u3-02-03.html)


Stitt29's comment on this (although irrelevant because the size of any mountain range has nothing to do with the planet's cooling rate or alleged heating rate,
it does - well, it's a factor limiting maximum relative height ...


Yes, all that is relevant and correct. That said, geologists have concluded that the Appalachians were once as big as the Himalaya, or on that order.
it's certainly fair to say that the Appalachians at their highest were "the Himalayas of their age" ... and in terms of order of magnitude, yes ...

[cran]

From Wikipedia (cope steps back to avoid blasts at Wikipedia as a source): "Cooling is the transfer of thermal energy via thermal radiation, heat conduction or convection. "
true enough ... but so is "heating" ...


Just because the heat is being replenished, there is still a net loss of heat energy by the Earth of something like .075 watts/square meter.

I'm just saying...
and saying it better this time ...

both (heating and cooling) process are occurring, but it's the nett outward flux (the "net loss") that defines the long term trend (of internal cooling) ...

[Romanus]

RE OP:
The Earth's interior is cooling--due to both decay of radionucleides and just regular energy loss through subduction, seafloor spreading, and eruptions--but not enough to gum up the works for some time.

[stitt29]

The Earth's interior is cooling--due to both decay of radionucleides and just regular energy loss through subduction, seafloor spreading, and eruptions--but not enough to gum up the works for some time.

decay of radionucleides is a source of heat. Subduction will also generate heat and add to internal pressure. Seafloor spreading, eruptions will cool the Earth, but heating overall.

A cooling Earth would require a contracting Mantle. Is the Earth getting smaller?

[cran]

decay of radionucleides is a source of heat. Subduction will also generate heat and add to internal pressure. Seafloor spreading, eruptions will cool the Earth, but heating overall.

A cooling Earth would require a contracting Mantle.
yes ... and an accumulating inner core ... and a thickening crust ...


Is the Earth getting smaller?
in your lifetime? not so you would notice - as with other aspects of the Earth, there are offsets ...

over the past 4 billion years? yes - most recent estimate I've encountered is ~1% radially.


you haven't explained how an Earth heating up internally would produce cooler magmas and lavas over time - ie, the shift from ultramafics to mafics ...

the hottest modern lavas are basaltic (mafic), and average ~1150 deg C at surface ...
the hotter Archaean lavas were komatiitic (ultramafic), and had to have erupted at 1400 deg C or more (the temperature required to form those mineral associations and produce the flow patterns found) ...

some mineral and metal associations only form at specific pressure and temperature ranges (eg chrome-nickel-PGEs); we can map the in-situ deposits (and distinguish from the transported deposits), determine the formation ages of the host rocks (using both relative and radiometric methods), and correlate the mineral formation properties against time ...
guess what? higher temperature mineral formations are consistently older than lower temperature formations ...


if you wish to pursue the line that the internal Earth is heating up, then this discussion really does belong in ATM ...
because it leads to the EE (Expanding Earth) and georeactor ideas.