Editing 3171: Geologic Core Sample

{{comic
| number    = 3171
| date      = November 21, 2025
| title     = Geologic Core Sample
| image     = geologic_core_sample_2x.png
| imagesize = 493x790px
| noexpand  = true
| titletext = If you drill at the right angle and time things perfectly, your core sample can include a section of a rival team's coring equipment.
}}

==Explanation==
{{incomplete|This page was created BY A GEOLOGIC RIBBIT. Don't remove this notice too soon.}}

This image presents a core sample taken by a slightly overenthusiastic team of geologists. 

A {{w|core sample}} is a cylindrical piece of something, in this case the rock of Earth's crust, obtained with special drills, taken in order to study the layers within. In typical xkcd fashion, the core sample depicted here contains a mix of real rocks found in core samples, and many humorous or fictional additions. It's shown that, on the way down, the coring drills have hit many, many obstacles they really shouldn't have, culminating in the punchline that the geologists have drilled straight through the Earth to the opposite hemisphere and out the other side — far deeper than any core sample could be taken in reality. In the real world the deepest borehole is the [[1330: Kola Borehole]] which attained maximum true vertical depth of 12,262 metres (40,230 ft; 7.619 mi) in 1989. 

;Topsoil             :{{w|Topsoil}} is the uppermost layer of the typical {{w|pedosphere}}, which often needs to be dug through before reaching actual rock. Whether the soil section of the core would actually be retained and counted is up to the nature of the study being made, but it will become clear that this core sample wasn't obtained with much thought of finesse.
;Till                :{{w|Till}} is unsorted glacial sediment, which might underlie the soil layer and form the transition to the foundation rock below.
;Granite bedrock     :{{w|Bedrock}} is solid rock, and there may normally be nothing but more bedrock beneath it until the Earth's {{w|Mantle_(geology)|mantle}}. {{w|Granite}} is a very common igneous rock that could normally form such bedrock.
:There are suggestions, from what is seen beneath it, that this particular layer of 'bedrock' (though being a natural material, at source) has been placed here as a construction base, infilled over with the above layers in this particular spot. 
:Bedrock could also be a reference to the unmineable blocks that make up the bottom of the world in Minecraft.
;Bottomsoil          :A fictional counterpart of topsoil. Topsoil is so named because it is generally found on top of other layers, and not to distinguish it from a separate 'bottomsoil' layer. Here, however, there are apparently two layers of soil somehow sandwiching the bedrock layer. Theoretically, the intervening granite could have been laid (as a slab) upon the lowest layers of an excavated area, later to be sampled by this corer ''as if'' a natural layer.
;Roof/Floor of subway car :These two layers are indications that the drill has broken into a subway tunnel (possibly from amongst those shown in [[1196: Subways]]), dug deep into the rock, or perhaps {{w|Tunnel#Cut-and-cover|cut'n'covered}} into the ground (hence, perhaps, the anomalous granite being added above — though the further tunnel lining/ceiling is not given a label, that would hold up the initial infill of soil). The section of tunnel it penetrated happened to contain a subway train, which has also been 'sampled'. The drill has essentially compressed the 'void' that is the interior of the car and the rest of the tunnel. This may seem to be good luck (given a later layer), but this still doesn't bode well for the subway train that may have been trying to move when the drill started to pierce it.
;More granite        :Granite ''is'' a very common igneous rock.
;Municipal water main:A pipe has been partly sliced through (enough to one side to not force the collapse of its void). Most water pipes of this size would not normally be forced through rock, only the loose material above it, relying upon pressure to carry water upwards, where necessary.
:However, {{w|combined sewer|drainage systems}} (that rely upon gravity for most of the route) may need at times to be dug deeper to maximize the natural flow. Some {{w|Thames Tideway Tunnel|particularly large projects}} may be excavated deeply through rock, even below some subway lines, though they'll be tunnels/pipes with a far larger bore than seen here, for both construction and capacity reasons.
;Slightly different granite:There are {{w|QAPF diagram|''many'' subtypes}} of granite, as well as being a lot of it.
;Piece of screaming spelunker's arm:Cave systems exist underground in many places, though more usually within rock-types more likely to dissolve than granite layers. The main exception might be from {{w|Lava tube|volcanic tunnels}} left in {{w|basalt}}, but that's technically ''still'' not granite, meaning that any cave system here would need explaining.
:{{w|Spelunkers}} (also known as cavers) explore caves, and one must have been in the wrong place when the corer passed through, suffering a clear injury (possibly greater than any that the unknown (but not ''directly'' impacted) subway users might have already suffered). If the spelunker was not already screaming ''before'' the drill came through (perhaps for help, if they were stuck — the size of the cave is unknown, with the open space closed up, as with the subway), losing a chunk of arm will have definitely prompted screams.
;Cool crystals with no resale value:There are many geological processes that can concentrate elements and compounds in a way that form crystalline minerals. Some are useful as ores, others are valued just as the crystals themselves (for aesthetic reasons or otherwise).
:Whatever these crystals are, as a small seam within the granitic layer just below the spelunker's location, they look nice (or are otherwise interesting), but either have little further application or are just so common that there's no point trying to make use of this deposit (even if they could perhaps be more 'easily' reached by any spelunker not put off by the threat of drillbits).
;Mangled fragments of drillbit from previous attempt
:When coring rock, it's possible for the tip of the coring drill to encounter problems (like particularly dense and hard rock) that damage it, perhaps by bending its track too much and shearing off the head.
:This latest attempt, probably sent down slightly to the side of the prior one (unless it had managed to gouge out ''just'' the remains of the previous drillpipe, and retain the rock/subway/spelunker layers previously cored out) has encountered the tip of the prior attempt.
:If there's one thing guaranteed to be as tough as a drillbit, it's ''another'' drillbit, which must necessarily be hard enough to cut through the expected rock types. Luckily, the first one was clearly damaged enough, by its prior encounter, that it didn't thwart this next attempt and (perhaps literally) grind it to a halt. Nor, apparently, was there a repeat of whatever issue left that first drill like this.
:Being in the middle of the core, it could be that these bits are meant to be from another attempt to drill the diameter of the Earth from a complete different location. Assuming absurd precision, all such drill holes would meet at the center of the Earth.  
;Some boring intrusive rock that's basically granite but has a name like "diorite" or "andalite" that you always have to look up
:Diorite is a real type of igneous rock — an intermediate between actual granite and {{w|gabbro}} — but an [http://animorphs.fandom.com/wiki/Andalite Andalite] is an alien from the Animorphs book series, which [[Randall]] enjoys and has [[:Category:Animorphs|referenced before]]. Perhaps Randall is "misremembering" the name of {{w|andesite}}, another type of igneous rock, from his [[1223: Dwarf Fortress|knowledge of]] the complex set of reality-inspired rock types encountered in the game {{w|Dwarf Fortress}}. As the sample appears right before the Netherrack sample, it may also be referencing {{w|Minecraft}}, as granite, diorite, and andesite exist in that game as mineable stone types.
;Netherrack:A dark red, and entirely fictional, stone appearing in Minecraft, with which Randall is [[861: Wisdom Teeth|also well acquainted]]. In Minecraft, Netherrack typically only appears naturally in The Nether, an alternate dimension resembling hell. In the overworld, where the core sample is presumably being taken, Netherrack only naturally forms in ruins of Nether Portals found on the surface, so for it to appear this deep in the sample, it would need to have been placed there by another person, likely while mining. (Some fan theories suggest that the nether is under the overworld, which isn't true, but some mods exist that make this true.)
;Balrog wing:The balrog is a creature in {{w|Lord of the Rings}}, found deep beneath the world, awakened when the dwarves delved too deep and too greedily, as it could be suggested that the geologists are doing here. It was previously encountered in the title text of [[3141: Mantle Model]]. The {{w|Balrog#Characteristics|balrog's wings}} are often discussed, in the context of whether it had them, and therefore whether they could or should have helped it escape the fall that was forced upon it in the books. At least one balrog, however, now appears to have at least one less wing than those it previously had. We do not know if there was any screaming involved.
;Granite:This label is applied to rock that appears to cover both ends of a 'height' of rock-core that is simplified by a diagrammatic cut. From the context of later layers, this would include a very long length of drilled material that passes into the {{w|Earth's mantle}}, and [[3145: Piercing|perhaps]] at least some of its core, before coming back up through the granite to be found somewhere on the other side of the planet.

; Topsoil:Beyond the indeterminate length of granite, the sample transitions back into the loose upper layers, indicating that the exploratory core is now being taken from ascending layers (albeit in a location lacking subways, etc, or just managing to miss everything seen in the preceding section).
;Cement:On emerging from the other side of the Earth, the geologists have drilled through the foundations of a building.
;Floorboards / Carpet:These two layers are typical of a reasonably well-equipped residential building — probably the ground floor, without any basement level. The core is coming up inside a furnished room.
;Possessions of a confused and angry homeowner in the other hemisphere
:The core sample has tunneled up into somebody's house, probably while they are there, and has traveled through some of the furniture, fixtures and/or fittings, to their clear annoyance.

Apart from the less expected elements to the core that was cut and retrieved (and the sheer impossibility of drilling the necessary several thousand miles 'down' through the Earth, and then drawing that sample back out again), the comic heavily plays upon the fact that someone with the ability and equipment to take this sample is, nevertheless, not as sure about geology as they perhaps ought to be, with almost all rock just being considered 'granite', without any better (or more accurate) qualification.

The title text suggests that core sampling is a competitive pursuit, in which, with the correct drilling angle, dark arts can be employed to interfere with the coring experiment of a "rival team". This is, outside of cold war-type pettiness, not considered a constructive approach to science.{{Citation needed}}

Only about 15% of the Earth's land surface is directly antipodal to other land, which would make this sample less than "typical" if it was aimed directly down through the exact centre of the Earth and back up again (a distance of almost 8,000 miles, or more than 12,000 km). If one were to do this from a random spot of land, one would be much more likely to have the sample terminate in an ocean; the chances of ending up in a house would be even lower. However, considering that the title text mentions drilling at an angle, the 'other hemisphere' point might be not necessarily be at the antipodal point, and there also seems to be the capacity to aim at a more desirable target, in which case this is a "typical" core under ''deliberately'' chosen circumstances. The exact nature of reaching "the other hemisphere" is not expanded upon — it could be as simple as drilling (mostly sideways) a short distance across the {{w|equator}}, or {{w|prime meridian}}, or having to go at least a quarter of the way of a great circle under the planet's surface (slightly over 1.4 times the Earth's radius, by the most direct route), in any direction, such that the two ends cannot be counted as being in any single arbitrary hemisphere.

This comic comes not long after [[3162: Heart Mountain]], which involved strange stratification, so may be part of the same thought process about the nature, and occasional oddities, of the geologic column.

==Transcript==
{{incomplete transcript|Don't remove this notice too soon.}}
:[Caption at the top of the panel:] Typical geologic core sample
:[Below this is a drawing of a cylindrical core sample with various labels, in order from the top of the panel toward the bottom.]
:[A short, dark section of core:] Topsoil
:[A more obviously granular shorter section with a diagonal transition:] Till
:[A light and lightly-marked phase:] Granite bedrock
:[Repeating the Topsoil appearance:] Bottomsoil
:[A short/squat and possibly squeezed 'lump':] Roof of subway car
:[A similar squeezed-out lump:] Floor of subway car
:[A longer length of the 'granite' texture, within which...:] More granite
:[Not quite half of a pipe-width, cut out as a gap perpendicular and not quite all the way across the core:] Municipal water main
:[Slightly more grainy version of the 'granite':] Slightly different granite
:[In a junction between 'granites', an squat, unidentifiable lump:] Piece of screaming spelunker's arm
:[Within a longer granite layer, a short stretch of spiky/crystalline features:] Cool crystals with no resale value
:[Within the same granite layer, an intrusion of mechanical-looking junk:] Mangled fragments of drillbit from previous attempt
:[As per granite, but slightly more grainy:] Some boring intrusive rock that's basically granite but has a name like "diorite" or "andalite" that you always have to look up
:[Dark, cobbly textured stone:] Netherrack
:[Within a stretch of granite, a short, dark but otherwise unidentifiable lump:] Balrog wing
:[At this point, there is a discontinuity indicating that an arbitrary length has been omitted. The sample then resumes:]
:[Still 'granite':] Granite
:[Dark soil texture:] Topsoil
:[Light, fine and sparse 'grains':] Cement
:[Two very short cross-sections, each with contrasting wood-grain stripes:] Floorboards
:[Two very short sections with a textile-base plus piles appearance:] Carpet
:[A mish-mash of 'stuff', possibly including cloth, metal components, grainy wood and 'topped' at the lowest end by something equally puzzling at an angle:] Possesions of a confused and angry homeowner in the other hemisphere

{{comic discussion}}<noinclude>
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