Editing 2242: Ground vs Air

{{comic
| number    =  2242
| date      = December 16, 2019
| title     = Ground vs Air
| image     = ground vs air.png
| titletext = Water is thinner than both, and fire is *definitely* thicker.
}}

==Explanation==

This comic depicts a map of the world using the {{w|Winkel tripel projection}}, comparing the thickness of the ground, which is defined as the {{w|lithosphere}}, to the "thickness" (or height) of the air above it, which refers to the {{w|atmosphere}}.

In an inserted figure, [[Randall]] defines the thickness using three boundaries. At the top is {{w|space}}, defined by the {{w|Kármán line}} at an altitude of 100 km (≈ 62 mi). (See the [[#Trivia|Trivia]] section below for a discussion of this definition of the beginning of space.) Below that is the atmosphere which goes down to the ground, where [[Cueball]] is standing, or the water. Beneath the surface is the lithosphere, comprised of the Earth's crust along with the rigid upper part of the mantle, and beneath this is the {{w|asthenosphere}}, the partially melted, highly viscous region of the {{w|upper mantle}} just below the lithosphere. The lithosphere is variable in thickness, averaging about 100 km, but the oceanic lithosphere is much thinner than the continental lithosphere (oceanic crust is thinner and denser than continental crust).  The diagram also shows oceanic cross-section to the left-hand side and, though the diagram does not make it explicit, presumably the two measurements used are of the atmosphere down from 'space' to the surface of the ground, if dry, or to the surface of the water covering the ground (which is essentially sea level in the oceans, fluctuating slightly with the tides, but covers a broader range for inland water, from the Dead Sea, at 0.4 km below sea level, to Lake Titicaca, almost 4 km above sea level) and of rock descending from the solid interface down to the asthenosphere, as the sliver of liquid that can intervene between the two spans is referred to as a separate measurement elsewhere.

The map shades in the parts where the thickness of the ground is thicker than the thickness of the air. This almost only occurs directly over continents, and certainly only where the continental crust is located (which can stretch into the near-coast parts of oceans). Oceanic crust is much thinner than continental crust. It is also made of a different material; it is denser. Because it is denser, it floats lower in the liquid asthenosphere, causing it to be below sea level. Some parts of continental crust are also under sea level (the continental shelf). These are the areas on the map that are marked as having thicker ground that appear to be over the ocean (such as Northern Canada, or the Caribbean) - they are actually still continental crust. (There are still some exceptions, such as the Sea of Japan and the Philippines). 

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 [https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2005GL025621 DOI.1029/2005GL025621]. Basically, Randall has taken their map and shaded the green and blue areas. It is the second comic in a row with a citation, after the footnote in [[2241: Brussels Sprouts Mandela Effect]].

The title text refers to the ancient four {{w|classical element}}s: earth, water, air, fire. The lithosphere, or ground, is earth, the oceans is water, the atmosphere is air, and fire would thus be the hot, plastic rock of the Earth's mantle, see [[913: Core]]. The mantle is not "on fire", but it is hot enough that it would ignite almost anything on the surface. The water layer on Earth is never more than 11 km deep, even at the deepest part of the ocean, the {{w|Mariana Trench}}, and thus cannot compare to the thickness of the atmosphere or the lithosphere. An expansive definition of "fire" to include the rest of the Earth below the lithosphere puts the fire layer at 6,000 km thick, the radius of the Earth, much thicker than the other layers, hence the ''and fire is *definitely* thicker'' comment at the end of the title text. Space or vacuum would in the classical element terminology have been called the {{w|Aether (classical element)|Aether}}.

In [[977: Map Projections]] the [[977:_Map_Projections#Winkel-Tripel|Winkel-Tripel projection]] is the fifth projection which is linked to the {{w|Hipster (contemporary subculture)|hipster}} subculture.

==Transcript==
:[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 the Indonesia, Western Africa, sub-equatorial Africa (labeled), and finally the central parts of Antarctica (labeled). Air is written on the West Coast of the United States, in the Atlantic Ocean, over the central part of Africa and in the Pacific Ocean, near the Philippines.]
:[Over West Coast of the United States]: Air
:[Over North America]: Ground
:[Over Atlantic Ocean]: Air
:[Over South America]: Ground
:[Over the central part of Africa]: Air
:[Over the southern 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 stands. 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.]
:Space
:Atmosphere
:Lithosphere
:Asthenosphere
:?

:[In the bottom right corner of the comic with gray text is a reference:]
:<font color="gray">Based mostly on Conrad and Lithgow-Bertelloni (2006) DOI.1029/2005GL025621</font>

==Trivia==
*[[Randall]] always uses the {{w|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 {{w|US Air Force}} and {{w|NASA}} in the title text of [[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. Mid-ocean ridges are where new crust is created and the plates are spreading apart; because the crust is new, it is hot and relatively less dense, causing it to float higher up than the surrounding crust. However, the lithosphere thickens over time as the crust cools, these areas have the thinnest "ground."
***Because the lithosphere is comprised only in part of the crust, and in part of a cool, solid layer of mantle, an alternate definition of "ground" including only the crust (and not the mantle lithosphere) could have led to an alternate version of this map where air was thicker in all locations. The crust is rarely more than 70 km thick, still less than even the 80 km Air Force definition of the atmosphere.
**Although most authorities use the FAI definition of the Kármán line since it is the international organization of record for aeronautics, there are good scientific reasons for the U.S. Air Force definition.{{Citation needed}}
**The Kármán line is named for {{W|Theodore von Kármán}}, who originally calculated the height at which a vehicle would have to travel faster than orbital velocity to generate lift from wings (therefore making the vehicle a spacecraft in orbit rather an "air"craft using aerodynamics for flight).  
**Von Kármán originally calculated this height as 51.9&nbsp;miles (83.6&nbsp;km) - closer to the Air Force definition.  
**Additionally, the boundary between the {{W|Mesosphere}} and the {{W|Thermosphere}} is traditionally taken to be 52.7&nbsp;miles (85&nbsp;km), also close to the Air Force definition. 
**On the other hand, some newer research suggests the mesopause (the line between the mesosphere and thermosphere) may have peaks between 53 and 62 miles (85-100 km). 
**Also the {{w|turbopause}} - the line where gas molecules cease mixing atmospherically and begin stratifying by molecular weight as if they are in orbit - is generally taken to be about 100 kilometers (62 miles), and as such, closer to the FAI definition. 
**Regardless of which definition is used, the reality is that the transition from atmosphere to space takes place gradually over tens of kilometers.
***But the idea behind this comic is only funny if an atmosphere of 100 km thickness is used.

{{comic discussion}}
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[[Category: Comics featuring Cueball]]
[[Category:Maps]]
[[Category:Geology]]
[[Category:Space]]