3171: Geologic Core Sample

Geologic Core Sample

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Title text: 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.

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Explanation

This is one of 52 incomplete explanations: This page was created BY A GEOLOGIC RIBBIT. Don't remove this notice too soon. If you can fix this issue, edit the page!

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

A 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  

Topsoil is the uppermost layer of the typical 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  

Till is unsorted glacial sediment, which might underlie the soil layer and form the transition to the foundation rock below.

Granite bedrock  

Bedrock is solid rock, and there may normally be nothing but more bedrock beneath it until the Earth's mantle. 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 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, 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 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 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 volcanic tunnels left in basalt, but that's technically still not granite, meaning that any cave system here would need explaining.

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 gabbro — but an Andalite is an alien from the Animorphs book series, which Randall enjoys and has referenced before. Perhaps Randall is "misremembering" the name of andesite, another type of igneous rock, from his knowledge of the complex set of reality-inspired rock types encountered in the game Dwarf Fortress. As the sample appears right before the Netherrack sample, it may also be referencing 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 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 literally true in-game, but some mods exist that make this true.)

Balrog wing

The balrog is a creature in 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 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 Earth's mantle, and 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 equator, or 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

This is one of 27 incomplete transcripts: Don't remove this notice too soon. If you can fix this issue, edit the page!

[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

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Discussion

F1R5T P0ST Slothscript (talk) 23:51, 21 November 2025 (UTC)

How do I add a category? It needs to be in the LOTR category. (Wow it’s hard to edit this thing on a phone) Kirinhatchi (talk)

is netherrack a typo? 151.197.190.53 (talk) 00:24, 22 November 2025 (UTC) (please sign your comments with ~~~~)

No, it's an extremely weak, dark red rock from Minecraft. RadiantRainwing (talk) 00:39, 22 November 2025 (UTC)

andalite is not a rock it's an alien from Animorphs which the author is a fan of. Maybe I'll add it to the Animorphs category page Whoservelt (talk) 00:28, 22 November 2025 (UTC)

They’re just normal rock types, so perhaps not, but I was wondering if the back-to-back references to granite and diorite is a secondary Minecraft reference, since they were added in the same update (which I always associate with them in general.) KelOfTheStars! (talk) 01:23, 22 November 2025 (UTC)

I think it IS another Minecraft reference. Along with granite and diorite, there’s a third in that triad: andesite — which is spelled and pronounced similarly enough to “Andalite” that the two could quite possibly be conflated, especially by someone who is familiar with the latter and “always has to look up” the former. 2a04:4e41:3521:69d6::1d21:69d6 (talk) 01:44, 22 November 2025 (UTC) (please sign your comments with ~~~~)

Well, it's 'andalite' in the comic, not andesite. I think that's just a passing reference. --DollarStoreBa'al^Converse 02:29, 22 November 2025 (UTC)

It's been a long time since I Minecrafted, but I don't recall any (stock) inclusion of anything so realistic. Raw 'generic' stone (which became cobblestone once mined, unless it was an ore-holding version), sandstone, obsidian (which I'd usually cast) and the indestrutable bedrock - in the 'normal' world. Netherack (I keep wanting to type "nethack"!) in the Nether and maybe something else (other than the general igneous theme, fire and hostiles) ...glowstone? I know there are (were) 'real rock patches', as with many other mods, but I hadn't heard of this being put into vanilla editions (Bedrock, or whatever). Whether it's happened since the Ender got put in, I don't know. I was playing (solo-survival mode, mostly) when there were Endermen, but not yet their own domain for them/the dragon, and basically forgot about it before Microsoft took it on (then had too many other new time-sinks to even consider selling my soul to them)...

But something like Dwarf Fortress does have plenty of rock-types (plain 'granite', but also diorite, gabbro, slate, limestone, mudstone, etc, etc, etc, even before getting to ores and gem clusters), for longer even than Minecraft had been around, and I linked into that where I thought appropriate. 82.132.236.186 17:26, 22 November 2025 (UTC)

You've not minecraft in a long time then friend, it's been over a decade since Endermen were added. Here are some more stone types in vanilla minecraft other than the ones you listed: Granite, Andesite, Diorite, Sandstone, Red Sandstone, Tuff, Deepslate, Calcite, Dripstone, Basalt, Blackstone, and End Stone. 199.247.247.123 19:20, 22 November 2025 (UTC)

As another long-lapsed minecrafter, that's news to me. (Could I colour stone, back then, or was that just wool blocks and maybe some modded-in 'concrete'?) Also reminded me more of DF stones, though, there being a lot of those, and MC looks like it's still not quite as complexity. I love being able to build entire castles in olivine, or cinnabar/whatever's plentiful enough (and not ore/flux, or the limited amount best saved for other purposes like colour-coded magmasafe floodgates/levers), without 'cheating' by applying my own hues to them. Mind you, I also prefer pre-Steam ASCII-style (vanilla) DF, as well, easier to understand, sometimes, than trying to understand some of the artwork. 2.98.77.121 20:08, 22 November 2025 (UTC)

Concrete is now an actual thing in minecraft. It's color is basically solid, So it's great for building. --DollarStoreBa'al^Converse 00:12, 23 November 2025 (UTC)

Do we make this a table? This comic seems perfect for a table. Maybe 'layer', whether it's real or not, and explanation? --DollarStoreBa'al^Converse 01:36, 22 November 2025 (UTC)

I'll try to work on a a table (given that someone else doesn't beat me to the chase). Also-what happened to your sig? 42.book.addict^{Talk to me!} 06:31, 22 November 2025 (UTC)

I was pondering a ";term:definition" approach, and someone beat me to it (but without the definition-indent) and I ran my changes with it. I don't think a table would need more than two columns (excluding "Real?", being "Yes", "No" or "Technically Yes/No, but..."), so, with the predicted division of vertical space in a table, I think I'd stick with the header+explanation of the ";:" method. (Can always add a Real/Not Real {{Yes}}/{{No}}/{{Maybe}}-like appending/prepending note to the term-header...) It's not really going to need sortable-table use, etc. 82.132.236.186 17:26, 22 November 2025 (UTC)

Should reference somewhere that Balrogs having wings is controversial to begin with (see here)[1] 2601:241:8002:3E0:89D3:137:DFC1:D5B4 04:41, 22 November 2025 (UTC)

Hadn't read this, when I puut my own thing about it in there. The actual "did they have wings?" bit, in the Balrog page I linked to a section of, is buried within a multiparagraph section, so maybe your link is better (or a better one in that part, straight-link Balrog on the first mention for the general wikipedia entry).

Certainly, when I was young (long before Wikipedia, and indeed the Web... Not sure when alt.fan.tolkien started, but I didn't have usenet access before I had academic internet access, but it was already an FAQ when I finally got into that scene), the questions were:

1. So, did a (or 'the', or any, depending on tye context) Balrog have actual wings?
2. If they did, why? Given they were subterranean denizens? (Probably not the exact words, maybe "...living underground".)
3. So how could it be made to fall like that? (Typical answer: "A wizard did it"... Namely Gandalf kept it falling/distracted. Because that was the point.)

...I may check to see if the collected wisdom of the current ubiquitous fan-led website has any better answers than we would come up with, after our countless geek-hours of discussion after/before/during tabletop RPGing (even if it wasn't LOTR-based, someone could easily have mentioned the balrog, in the context of a viking attack over a narrow bridge, or whatever). 82.132.236.186 17:26, 22 November 2025 (UTC)

Balrogs are not naturally subterranean. They're Maiar, just like Sauron and Gandalf. They used to fight in wars and do other evil stuff on the surface. DL Draco Rex (talk) 15:33, 23 November 2025 (UTC)

Actually, coring previous drilling equipment can happen. The southern German town of Staufen suffered a geothermal drilling gone wrong (they inserted ground water into anhydrite, which swelled, causing the town to rise). During the investigations, the original drilling equipment was hit in the new core, showing the errors made in the first place. 2001:16B8:A875:DC00:3068:165E:B396:DE72 07:33, 22 November 2025 (UTC)

Side comment on the header saying "typical": coming to the surface on land instead of water is extremely unlikely, as we were taught years ago by Ze Frank's "If The Earth Were a Sandwich" video series. Look it up. Jonesey (talk) 16:24, 23 November 2025 (UTC)

The explanation talks about how the Nether is essentially Minecraft hell - it might be worth mentioning how the comic might be referencing going so deep you find hell. That might also coincide with the Balrog wing (do they live in hell?), something something digging too deep, but I lack the requisite LOTR knowledge to make that connection for real R128 (talk) 13:50, 24 November 2025 (UTC)

Also, they've ended up coring another person's house, and as we all know, hell is other people...

Oh, and there's a bit of water main in there, and the main is, of course, high water. 82.13.184.33 14:30, 24 November 2025 (UTC)

Probably the Kola Superdeep Borehole should be mentioned.Rps (talk) 16:44, 24 November 2025 (UTC)

This also has a related comic 1330: Kola Borehole --134.102.219.31 16:53, 24 November 2025 (UTC)

Switched out the balrog reference in 730: Circuit Diagram for the one in 3141: Mantle Model, since the former felt way too indirect of a reference to be relevant here, and the latter is a lot more directly tied to geology.KelOfTheStars! (talk) 19:22, 24 November 2025 (UTC)
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