<p>Except for <a href="https://www.reddit.com/r/askscience/comments/27jvt3/is_it_true_that_water_is_the_only_substance_on/" rel="noreferrer">ice, acetic acid, bismuth and gallium</a> and a few other things materials generally shrink when they cool and solidify, so I'm pretty sure Earth has as well.</p>

<p>It probably wouldn't be measurable over a period of years, but models of the Earth's current and historic rates of heat flow can probably be used to estimate a rate of change of Earth's average size and possibly oblateness.</p>

<p>Right now <a href="https://en.wikipedia.org/wiki/World_Geodetic_System#A_new_World_Geodetic_System:_WGS_84" rel="noreferrer">WGS84 uses</a> 6378137.0 meters for Earth's equatorial radius and a flattening at the poles of about 1/298.257222. </p>

<p>How fast might those change over any given million years?</p>

CC BY-SA 4.0
2020-03-01T05:01:08.740Z
Perhaps relevant question: https://earthscience.stackexchange.com/q/18534/15419
BMF
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2020-03-01T05:06:57.573Z
@BMFForMonica Thanks! That's close but I don't think it's a duplicate. It's possible that an answer can be written here based on estimating the slopes shown in Figure 2 of the link in an answer there if we assume that most of the change is due to the mantle. But I'm not sure if those assumptions are correct.
uhoh
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2020-03-02T02:55:24.337Z
keep in mind the earth is slowly gaining mass due to meteors. Its a small effect but on the scale involved likely bigger than thermal changes.
John
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2020-03-02T02:57:03.083Z
@John [good point!](https://earthscience.stackexchange.com/q/16688/6031) ;-)
uhoh
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2020-03-05T14:16:41.793Z
Do you factor the water into the size?   Earth may be losing mass overall due to loss of hydrogen and some helium, in greater amounts than the added mass by meteors, that said, meteors contribute to the surface.   The loss of water (by loss of hydrogen) is more tricky.   Are you defining size by sea level or by average rock altitude, which would be over a mile lower given average sea level depth of about 2.3 miles).   https://earthscience.stackexchange.com/questions/16688/is-earth-getting-heavier-or-lighter?noredirect=1&lq=1
userLTK
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2020-03-05T14:39:33.117Z
@userLTK it's an important question, I wouldn't want to pre-define something that made an answer harder, so if there's a good answer either way it would probably be accepted. If it can be demonstrated that the question can't be answered with a rate, than that would be an acceptable answer as well. However, the link in the first comment seems to provide some means to an approximate answer without considering water, so if nothing else is forthcoming, that might be good enough.
uhoh
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2020-07-29T22:36:47.300Z
@a_donda I think that you can undelete that and maybe add a block quote of a few sentences from the abstract (so the answer still makes sense if the link breaks) and I can accept it. In any even thanks for the link, that's quite an interesting paper!
uhoh
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2020-07-29T23:38:40.147Z
@a_donda I guess at 10k reputation deleted posts are still displayed. In Stack Exchange nothing is ever really deleted, it just "fades from view" for most users. When I saw "linked article" in your comment and didn't see a linked article in my question, I scrolled down and saw it. https://i.sstatic.net/b8Lvq.jpg
uhoh
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2020-12-03T09:23:48.627Z
Did you factor space dust and meteorites arriving? that's 100 metric tons of this cosmic dust enters Earth's atmosphere every single day. also there is some loss from the top of the atmosphere.
bandybabboon
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2020-12-03T09:51:41.417Z
@aliential I've *asked* the question, not answered it. However we can estimate that at that rate it would take several years to build up a 1 atom thick layer, something like a million years would be 100 microns, and that's ignoring any compression due to the added weight.
uhoh
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2020-12-03T09:58:05.303Z
The deepest layers of the planet are not well understood, so we don't know if the internal heat is constant/variable or reducing due to nuclear processes, AFAIK, I'd suggest it's a shot in the dark.
bandybabboon
<geophysics><models><earth-history><thermodynamics>
How quickly is the Earth shrinking?
uhoh
# How quickly is the Earth shrinking?

(Asked by: username_0 on 2020-03-01)

Except for [ice, acetic acid, bismuth and gallium](https://www.reddit.com/r/askscience/comments/27jvt3/is_it_true_that_water_is_the_only_substance_on/) and a few other things materials generally shrink when they cool and solidify, so I'm pretty sure Earth has as well.

It probably wouldn't be measurable over a period of years, but models of the Earth's current and historic rates of heat flow can probably be used to estimate a rate of change of Earth's average size and possibly oblateness.

Right now [WGS84 uses](https://en.wikipedia.org/wiki/World_Geodetic_System#A_new_World_Geodetic_System:_WGS_84) 6378137.0 meters for Earth's equatorial radius and a flattening at the poles of about 1/298.257222.

How fast might those change over any given million years?

**Tags:** geophysics, models, earth-history, thermodynamics

> **Comments:**
> **username_1**: Perhaps relevant question: https://earthscience.stackexchange.com/q/18534/15419  
> **username_0**: @BMFForMonica Thanks! That's close but I don't think it's a duplicate. It's possible that an answer can be written here based on estimating the slopes shown in Figure 2 of the link in an answer there if we assume that most of the change is due to the mantle. But I'm not sure if those assumptions are correct.  
> **username_2**: keep in mind the earth is slowly gaining mass due to meteors. Its a small effect but on the scale involved likely bigger than thermal changes.  
> **username_0**: @username_2 [good point!](https://earthscience.stackexchange.com/q/16688/6031) ;-)  
> **username_3**: Do you factor the water into the size?   Earth may be losing mass overall due to loss of hydrogen and some helium, in greater amounts than the added mass by meteors, that said, meteors contribute to the surface.   The loss of water (by loss of hydrogen) is more tricky.   Are you defining size by sea level or by average rock altitude, which would be over a mile lower given average sea level depth of about 2.3 miles).   https://earthscience.stackexchange.com/questions/16688/is-earth-getting-heavier-or-lighter?noredirect=1&lq=1  
> **username_0**: @username_3 it's an important question, I wouldn't want to pre-define something that made an answer harder, so if there's a good answer either way it would probably be accepted. If it can be demonstrated that the question can't be answered with a rate, than that would be an acceptable answer as well. However, the link in the first comment seems to provide some means to an approximate answer without considering water, so if nothing else is forthcoming, that might be good enough.  
> **username_0**: @a_donda I think that you can undelete that and maybe add a block quote of a few sentences from the abstract (so the answer still makes sense if the link breaks) and I can accept it. In any even thanks for the link, that's quite an interesting paper!  
> **username_0**: @a_donda I guess at 10k reputation deleted posts are still displayed. In Stack Exchange nothing is ever really deleted, it just "fades from view" for most users. When I saw "linked article" in your comment and didn't see a linked article in my question, I scrolled down and saw it. https://i.sstatic.net/b8Lvq.jpg  
> **username_4**: Did you factor space dust and meteorites arriving? that's 100 metric tons of this cosmic dust enters Earth's atmosphere every single day. also there is some loss from the top of the atmosphere.  
> **username_0**: @aliential I've *asked* the question, not answered it. However we can estimate that at that rate it would take several years to build up a 1 atom thick layer, something like a million years would be 100 microns, and that's ignoring any compression due to the added weight.  
> **username_4**: The deepest layers of the planet are not well understood, so we don't know if the internal heat is constant/variable or reducing due to nuclear processes, AFAIK, I'd suggest it's a shot in the dark.  

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## 0 answers

