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 soil.
;Till                :{{w|Till}} is unsorted glacial sediment.
;Granite bedrock     :{{w|Bedrock}} is solid rock and there may normally be nothing but more beneath it, than more bedrock, before reaching the Earth's mantle. {{w|Granite}} is a very common igneous rock that could normally form such bedrock.
:There may be indications, from what is seen beneath it, that this particular layer of bedrock, whilst being a natural material, has been placed here as a construction material
;Bottomsoil          :This is a fictional counterpart of topsoil, on the basis that it is somehow sandwiching the bedrock layer. Theoretically, however, the granite above could have been laid upon the lowest layers of the {{w|pedosphere}}, to be sampled by this corer ''as if'' a natural layer.
;Roof of subway car
;Floor of subway car :The drill has broken into one of these, dug deep into the rock (or bottomsoil!) of the area, possibly from amongst those shown in [[1196: Subways]]. The drill has essentially compressed the 'void' that is the interior of the car, 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 moving 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 dug into 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 way, may need at times to be dug deeper. Some {{w|Thames Tideway Tunnel|particularly large projects}} may be excavated through rock, though they'll be tunnels/pipes with a much larger bore than seen here.
;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 in granite layers, except perhaps for {{w|Lava tube|volcanic tunnels}} left in {{w|basalt}} (''still'' not granite).
:{{w|Spelunkers}} explore caves, and one must have been in the wrong place when the corer passed through, with a clear injury possibly greater than any thst the subway users might have already suffered.
;Cool crystals with no resale value:There are many geological processes that can concentrate elements and compounds in a way that form crystelline minerals. Some are useful as ores, others as just the crystals themselves (for aesthetic reasons or otherwise).
:Whatever these crystals are, they look nice (or are otherwise interesting), but either have so little further use or are just so common that there's no point trying to find these (even if they could perhaps be '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 rock) that damage it, perhaps by bending its track too much.
:This latest attempt, probably sent down slightly to the side of the prior one (unless it had managed to gouge out ''just'' the drillpipe, and retain the rock/subway/spelunker layers previously drilled into) has encountered the tip of the prior attempt.
:If there's one thing as tough as a drill-bit, it's ''another'' drill-bit, so it's lucky that the first one was clearly damaged enough, by its prior encounter, that it didn't thwart this next attempt. Nor, apparently, did 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

;    Netherrack
A dark red stone appearing in the Nether in {{w|Minecraft}}
;    Balrog wing
A creature in {{w|Lord of the Rings}} awakened when the dwarves delved too deep and too greedily
;    Granite
;    Topsoil
A reversal of the normal layers, as the core sample has gone all the way through the earth
;    Cement
;    Floorboards
;    Carpet
;    Possesions of a confused and angry homeowner in the other hemisphere
The core sample has tunneled up into somebody's house.


Contained within it are fairly normal ground matter such as "topsoil" and "granite" but also such things as "bottomsoil", which has no IRL parallel, parts of subway cars, arms of a spelunker most likely amputated by the sample, netherrack (a dark red stone appearing in the Nether in {{w|Minecraft}}), a "balrog" wing (referencing a fictional animal from {{w|Lord of the Rings}} which first made an appearance in xkcd in [[730: Circuit Diagram]]).

After a discontinuity in the diagram, that would cover whatever might appear having driven through the core of the earth, there is a reversal of the more 'standard' layers and then some equally nonstandard layers. These indicate that it has tunneled up into the home of someone else, starting with cement (the foundation), floorboards and carpet, then their posessions.

While still on the side that is heading down, it also mentions other rocks that are "basically granite". As in the idea that many rocks are similar, but are called "{{w|diorite}}" or "andalite". Diorite is a real type of igneous rock, 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. This is likely another reference to Minecraft, which has all three rocks available in the overworld.

In reality, only about 15% of the earth's land surface is antipodal to other land, making this sample less than "typical". If one were to start on land and drill all the way through the center of the earth to a point on the other side of the world, one would be much more likely to have the sample terminate in an ocean than on land, much less in someone's house. Though considering that title text mentioned drilling at an angle, that other side might be not at the antipodal point.

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}}

This comic may be intended as a criticism of standard conceptions of the geologic column, challenging the assumption that geological strata necessarily correlate with time. Just as it is obvious that the possessions of the confused and angry homeowner are not the oldest part of the sample, followed by the carpet, and so on, it is equally fallacious to assume that geological strata in real samples represent periods of time.

==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]]
[[Category:Charts]]
[[Category:LOTR]]
[[Category:Animorphs]]
[[Category:Minecraft]]