Editing 2242: Ground vs Air

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, including the ocean down to the seafloor as indicated on the left side. 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 two measurements are between space and the surface, and the surface to the asthenosphere.

The map shades in the parts where the thickness of the ground is thicker than the thickness of the air. 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, northernmost Canada, 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 [https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2005GL025621 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]].

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. (Randall is likely referring to how the mantle is frequently represented in drawings as fiery red molten rock, even though the mantle is solid--none of it is magma or otherwise "on fire" except in small volumes at locations very close to the crust.) See [[913: Core]]. The water layer on Earth is never more than 11 km deep, even at the deepest part of the ocean in 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 6000 km thick, much thicker than the other layers.

***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.  

**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.