Editing 3171: Geologic Core Sample

{{comic
| number    = 3171
| date      = November 21, 2025
| title     = Geologic Core Sample
| image     = geologic_core_sample_2x.png
| imagesize = 493x789px
| 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 RIVAL GEOLOGY TEAM. Don't remove this notice too soon.}}

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

A {{w|core sample}} is a cylindrical piece of something's core, in this case the rock of Earth's crust, obtained with special drills in order to see the layers within. In typical xkcd fashion, the core sample depicted here contains a mix of real rocks found in core samples alongside many humorous or fictional additives. In addition it's shown that the coring drills have hit many, many obstacles on the way down they really shouldn't have impacted, culminating in a punchline the geologists have drilled straight through the Earth to the opposite hemisphere, far deeper than any core sample could be taken in reality.

;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-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 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.
;Bottomsoil          :This is a presumably fictional counterpart of topsoil, on the basis that they are both soil somehow sandwiching the bedrock layer. Theoretically, however, the above granite (as a slab) could have been laid upon the lowest layers of the excavated area, later to be sampled by this corer ''as if'' a natural layer.
;Roof of subway car 
;Floor of subway car :These two layers are indications that the drill has broken into a subway tunnel and through a subway train, possibly from amongst those shown in [[1196: Subways]], which will have been dug deep into the rock or perhaps {{w|Tunnel#Cut-and-cover|cut'n'covered}} into the ground (hence the anomalous granite added above later). The drill has essentially compressed the 'void' that is the interior of the car and the rest of the tunnel, which 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        :{{w|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 potentially {{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 are. 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}} explore caves, and one must have been in the wrong place when the corer passed through, being inflicted 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 as just 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 drill-bit, it's ''another'' drill-bit, which must necessarily be hard enough to cut through the expected rock-types. So it's lucky that 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.
;Some boring intrusive rock that's basically granite but has a name like "diorite" or "andalite" that you always have to look up
:Again, it's perhaps one of those granites. Diorite is a real type of igneous rock, an intermediate between actual granite and {{w|gabbro}}, but an 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 reaility-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 well, as Granite, Diorite, and Andesite exist in-game as a mineable stone type, but all three types are often infamous for clogging up inventories whilst mining, due to their exclusively decorative use.
;Netherrack:A dark red, and entirely fictional, stone appearing in the Nether in Minecraft, with which Randall is [[861: Wisdom Teeth|also well acquainted]].
;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, and previously encountered in [[730: Circuit Diagram]]. The {{w|Balrog#Characteristics|balrog's wings}} are often discussed upon, in the context of whether it had them, 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, without us knowing if there was also 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, it transitions back into the loose upper layers, indicating that it the exploratory core is now being taken from ascening layers, albeit in a location lacking subways, etc, or just managing to miss everything originally seen.
;Cement:This indicates and heralds the presence of a building, starting with its foundations.
;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.
;Possesions 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 unsettled 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 yet 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 humorously refers to a "rival team" and their coring equipment &mdash; implying that (with the correct angle) you can meddle with their own coring experiment. 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 woupd making 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 and the chances of ending up in given house would be even lower. Though 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.

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 of the geologic column.

==Transcript==
{{incomplete transcript|Don't remove this notice too soon.}}
:[This shows a drill sample with various labels, in order from the top of the panel toward the bottom.]
*Topsoil
*Till
*Granite bedrock
*Bottomsoil
*Roof of subway car
*Floor of subway car
*More granite
*Municipal water main
*Slightly different granite
*Piece of screaming spelunker's arm
*Cool crystals with no resale value
*Mangled fragments of drillbit from previous attempt
*Some boring intrusive rock that's basically granite but has a name like "diorite" or "andalite" that you always have to look up
*Netherrack
*Balrog wing
:[At this point, there is a discontinuity indicating that some layers have been omitted. The sample then resumes:]
*Granite
*Topsoil
*Cement
*Floorboards
*Carpet
*Possesions of a confused and angry homeowner in the other hemisphere

{{comic discussion}}<noinclude>
[[Category:Geology]]
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[[Category:Animorphs]]
[[Category:Minecraft]]