2242: Ground vs Air

Explain xkcd: It's 'cause you're dumb.
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Ground vs Air
Water is thinner than both, and fire is *definitely* thicker.
Title text: Water is thinner than both, and fire is *definitely* thicker.


Ambox notice.png This explanation may be incomplete or incorrect: Created by a THICK FIRE. More on the general thickness of the "ground", especially on the oceans and at the thickest parts. Needs more about the actual data portrayed.
If you can address this issue, please edit the page! Thanks.

This comic depicts a map of the world, using the Winkel tripel projection, comparing the thickness of the ground, which refers to the lithosphere, to the thickness of the air above it, which refers to the atmosphere.

In an inserted figure, Randall defines the thickness using three boundaries. At the top is space, defined by the Kármán line at an altitude of 100 km (≈ 62 mi). Below that is the atmosphere which goes down to the ground, where Cueball is standing, including the ocean down to the seafloor as indicated on the left side. Beneath the surface is the lithosphere, also known as the Earth's crust, and beneath this is the Asthenosphere, the highly viscous region of the upper mantle of the Earth. The two measurements are between space and the surface, and the surface to the asthenosphere.

The map shades in the parts where the second measurement is thicker than the first. This almost only occurs over continents, and certainly only where the continental plates are located (which can stretch into the shallow parts of the oceans). But there are several sections, such as in the Caribbean and the Sea of Japan, where the ground is thicker even being below sea level.

Randall has mainly used a work by Conrad and Lithgow-Bertelloni from 2006 to estimate the thickness of the "ground", and he gives the reference to the paper DOI.1029/2005GL025621. Basically, Randall has taken their map and shaded the blue areas. It is the second comic in a row with a citation, after the footnote in 2241: Brussels Sprouts Mandela Effect.

Randall always uses the Kármán line as the boundary between Earth's atmosphere and space. He has previously mocked the alternative definition of the atmosphere boundary (at 80 km ≈ 50 mi) used by US Air Force and NASA in the title text 1375: Astronaut Vandalism. That definition would, of course, have resulted in a significantly different picture where the air is thicker than the ground only inside small areas around mid-ocean ridges.

The title text referrers to the ancient four classical elements earth, water, air, fire. The lithosphere, or ground, is earth, the oceans is water, the atmosphere is air, and fire would thus be the various magma layers underneath the crust down to the center of the core. See 913: Core. The water layer on Earth is never more than 11 km deep at the Mariana Trench, and thus cannot compare to the thickness of the atmosphere or the lithosphere. Whereas there is fire all the way into the core so this layer is either 6000 km thick, or 12000 km, depending if Randall would look at the depth to the center or to the entire diameter of Earth. In either case it would always be much thicker than the roughly 100 km or the other two layers.

In 977: Map Projections the Winkel-Tripel projection is the fifth projection which is linked to the hipster subculture.


[Caption above the drawing]:
Which is thicker—the ground or the air?
[The drawing shows a Winkel tripel projection of the Earth. The features of the main map is unlabeled, with only the outlines of the landmasses present. Various parts of the map are labeled with "Air" (four times) or "Ground (5 times)." Areas marked as "Ground" are differentiated with gray shading. These are always over large landmasses or close to them. They cover most of North America (labeled), the northern part of South America (labeled), Northern Europe and most of Asia (labeled), Japan, Most of Australia and part of sea above, Western Africa, the part of Africa beneath Equator (labeled), and finally the central parts of Antarctica (labeled). Air is written on the East coast of America, in the Atlantic Ocean, over the central part of Africa and in the Pacific Ocean east of China.]
[Over East coast of America]: Air
[Over North America]: Ground
[Over Atlantic Ocean]: Air
[Over South America]: Ground
[Over central part of Africa]: Air
[Over south part of Africa]: Ground
[Over Asia]: Ground
[Over Pacific Ocean]: Air
[Over Antarctica ]: Ground
[A small diagram is present in the Pacific Ocean left of South America. The diagram depicts several labeled layers of Earth and its atmosphere, listed below. Cueball, a body of water, and several mountains are shown on the flat surface part of the diagram, with the ocean floor lower than where Cueball stand. Above is a line representing the border to space. The line beneath the surface is much more curved going both up and down. Two double arrows representing the thickness of the atmosphere and the Lithosphere are drawn between the surface and the layers above and below. Another curved double arrow is pointing to each of these distances and it is marked with a question mark in the middle of the line.]
[In the bottom right corner of the comic with gray text is a reference:]
Based mostly on Conrad and Lithgow-Bertelloni (2006) DOI.1029/2005GL025621

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Wow; it took longer than I care to admit to realize 'thick' wasn't 'viscosity'...but 'altitude'. (i.e., height/thickness re: Kynde's comment) Elvenivle (talk) 01:08, 17 December 2019 (UTC)

Ohhhhhhhh! Sdkb (talk) 02:38, 17 December 2019 (UTC)
Not altitude, but height or thickness... --Kynde (talk) 11:03, 17 December 2019 (UTC)
^ Yes, that. Correction added; I meekly blame word choice on keyboard dead zones. Elvenivle (talk) 20:22, 17 December 2019 (UTC)

A link to the article is here: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2005GL025621. 01:12, 17 December 2019 (UTC)

It's probably worth mentioning in the explanation which map projection Randall chose to use for this comic from those listed in a previous comic about map projections. Ianrbibtitlht (talk) 02:22, 17 December 2019 (UTC)

And by these metrics, blood is even thinner than water... Template:unsignedip

But everything changed when the fire nation attacked 10:47, 17 December 2019 (UTC)

I assume ocean ridges have a very thin crust, meaning they get the ratio more towards air? I am not at all a geologist, so I ask this question, because ridges would intiutively appear to have a bigger crust, as they stand out from the ground. "That definition would, of course, have resulted in a significantly different picture where the air is thicker than the ground only inside small areas around mid-ocean ridges" should be explained by someone who knows why it is the case. --Lupo (talk) 14:26, 17 December 2019 (UTC)

Mid-ocean ridges can even be raised above the ocean surface--Iceland is actually the high point on one of them. In other places they're trenches, though. Since seafloor crust is spreading at those points, it's at its thinnest there on average. Nitpicking (talk) 02:08, 18 December 2019 (UTC)
Would you feel confident, adding that in a concise way to the explanation? I do not... But I am glad I learned something by that. That might also explain why these ocean ridges tend to be equipped with volcanoes. I thought the reasoning was the other way round: They are ridges due to their geothermal activity. --Lupo (talk) 07:27, 18 December 2019 (UTC)
I have done this! And added a bit more earth science knowledge besides. And while Iceland is the highest point on the ridge, I'm not sure I'd say it's actually because of the ridge - Iceland is a hot spot the same way Hawaii (which is not on a ridge) is. 21:29, 30 January 2020 (UTC)

The current explanation seems to include water-thickness in with (either) air or ground thickness in discussing it in the initial transition from air to ground. Depends how you read it, which, but it easily reads as either. Maybe edit that aside out from that bit, then make sure that sliver of water is gone into later (...end of that para? ...footnote mention?) that sometimes the air ends at sea-level and ground starts after the depth of sea? 12:28, 18 December 2019 (UTC)

Just done what I think you asked for, as luck would have it. (And then redid it slightly to avoid adjectival and verb forms of "separate" appearing so close together.) 19:46, 18 December 2019 (UTC)

The current explanations refers to fire as being 12000km, I would rather go with the radius of 6000km. Makes more sense to me since we are on a sphere and not counting the crust thickness twice. 17:52, 18 December 2019 (UTC)

Should we make a Comics with Citations category? Seems like it's warranted 19:21, 18 December 2019 (UTC)

XKCD is he only webcomic where mentioning the type of map projection in an explanation would not be needless pedantism. —Kazvorpal (talk) 18:52, 22 January 2020 (UTC)