2925: Earth Formation Site

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Earth Formation Site

Title text: It's not far from the sign marking the exact latitude and longitude of the Earth's core.

Explanation

Cueball reads an historical marker celebrating the formation of the Earth. As with most historical markers, it claims to rest on the exact spot of the event, that the Earth formed in this specific location. It also specifies the Earth's formation to the precise year 4.45 billion (4,450 million) BCE.

The absurdity of the sign is threefold:

1. The Earth did not form on its surface
2. The precise year of the Earth's formation is not knowable
3. Historical markers typically refer to events within the past several centuries

#1: The Earth did not form on its surface

First, the Earth formed at its center, not anywhere on its surface, so an “Earth formed here” sign on the surface is amusingly incorrect.

One may argue that technically the sign is above the right spot, just as every location on Earth is above the right spot. However, the sign refers to “this location,” not to a spot underground.

If an omniscient observer wanted to mark the spot in space where the Earth started forming, they would need an historical marker floating in space, not on the surface of the (moving) Earth. That’s due to the Sun's 225-million year long orbit around the center of the Milky Way galaxy and the movement of the galaxy itself through space relative to other objects.

#2: The precise year of the Earth's formation is not knowable

Secondly, specifying a single year of formation BCE (Before the Common Era) is an amusingly precise choice. It takes tens or hundreds of millions of years for a planet to form. Picking a year would require some specific definition of when a gradually-coalescing mass of proto-planet dust and gas could be considered a planet, as well as the impossible ability to determine when that mass met the definition.

If the precise year was knowable, the probability of the number actually ending in seven consecutive zeros would be on the order of one-in-ten-million.

The topic of what precisely makes a planet — related to the 2006 redefinition of a planet and the subsequent reclassification of Pluto from the solar system's ninth planet to a dwarf planet — has been covered before in 473: Still Raw and referenced in other XKCD comics.

There is some poetry in the idea that there was a precise year, some 4.45 billion years ago, that was the first true year, the first Earth orbit around the sun. By definition, the Earth is the same age as the number of Earth orbits that have ever taken place.

Note: The date shown for the formation of the Earth, 4.45 billion years ago, also differs from the commonly accepted date, 4.54 (±0.05) billion years. The difference lies in the transposition of two digits, 5 and 4, potentially a mistake, as is common in historical markers.

#3: Historical markers typically refer to events within the past several centuries

Historical markers are placed at precise locations where historical, religious, and even mythological events are believed to have happened — such as where battles have been fought, or where famous people resided or accomplished something. Typically these signs refer to more recent events.

The title text

The title text refers to the 'exact latitude and longitude of the Earth's core,’ Of course, since the lat-long geographic coordinate system is used for locating places on the surface on the Earth, the center of the Earth does not have latitude and longitude.

Also, a historical marker referring to the Earth’s core could be placed anywhere on the surface, and its specific location in the real world wouldn’t mean anything; just as before, every spot on Earth is above the right spot.

Examples of similar historical marker signs:

• Kenya Equator latitude
• Arctic Circle latitude
• Prime Meridian longitude
• Highest Point
• Lowest Point

Analysis

The comic and its title text are actually inverse jokes of each other: The historical marker in the comic assigns an attribute of the Earth’s center (the site of formation) to a spot on its surface, while the historical marker mentioned in the title text assigns an attribute of surface locations (latitude and longitude) to the Earth’s center.

Transcript

This transcript is incomplete. Please help editing it! Thanks.

[Cueball is standing in front of a sign in a field of grass. Rocks and plants are scattered across the ground. The sign reads:]

HISTORICAL MARKER

EARTH

FORMATION SITE

--- 4,450,000,000 BCE ---

At this location in the year 4,450,000,000 BCE, a cloud of dust and gas gravitationally collapsed to form the Earth.

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Discussion

The title text is only true for geocentric latitude and longitude, not geodetic (which is what is commonly used). 172.69.58.125 18:32, 26 April 2024 (UTC)

I'm impressed that whatever distant body that sign is placed upon, has actually developed plant life. Especially since it would need to be parked in place relative to the rest of the observable cosmos, & thus seems unlikely to have a suitably close star making regular appearance overhead... ProphetZarquon (talk) 19:11, 26 April 2024 (UTC)

👍Tier666 (talk) 09:52, 28 April 2024 (UTC)

Magrathea? L-Space Traveler (talk) 14:46, 27 April 2024 (UTC)

Hi Proph! I just wanted to say that I enjoy reading your comments here and in the SMBC comment page, if you are in fact ProphetZarquon in both places. 172.70.175.28 21:46, 26 April 2024 (UTC)

If there's another Prophet Zarquon out there - wait, nope, looks like that's me, too...

ProphetZarquon (talk) 03:25, 27 April 2024 (UTC)

The spatial location of a famous person's birth is technically not where the Solar System now is, also. If you're going to be picky about that. If you do allow the Earth's worldline to be accounted for, then it's broadly true that Earth formed (looks out of window at home) here. I think the principle concern there is whether Earth formed in the collision of planets named Ear and Theia, or whether Earth was Earth before Theia came along, which either way seems to be why there is such a large Moon beside it - made of material from both of the previous planets. And it probably counts as a change of course from the previous situation, although the apparent likelihood that Theia formed in Earth's orbit in originally a Trojan relationship may bear on that - if one planet just caught up with the other in orbit, like tailgating in traffic. [email protected] 141.101.98.184 17:35, 27 April 2024 (UTC)

The ridiculously specific date may be a reference to how real historical markers frequently get dates incorrect 172.70.127.135 23:29, 26 April 2024 (UTC)

The other side of the sign says, "At this exact point in space, 13.7878693 billion years ago, the Big Bang took place." That's true of every point in space, according to the current model. The Big Bang implies that all of space was a single point, and space itself expanded outward from that point. Nitpicking (talk) 03:07, 27 April 2024 (UTC)

The explanation needs to be rewritten. It is missing the point and far to detailed for just saying: The marker could be standing at any point of earth's surface, as reinforced by the title text. The whole discussion about galaxies and solar systems moving is just a matter of the reference system and does not contribute to the understanding of the comic.--172.70.243.32 07:28, 27 April 2024 (UTC)

I agree. All location markers on earth are relative to the earth itself [citation needed] and locations with the same lattitude and longitude are considered the same location, at least on maps. The explanation is missing te point, maybe even on purpose. 172.71.103.30 07:28, 8 May 2024 (UTC)

I disagree. The section is saying that it could not have reasonably happened on Earth itself due to the fact the Earth and the Solar System itself move around through space. someone, i guess^{(talk i guess|le edit list)} 13:25, 27 April 2024 (UTC)

Randall was once a physicist. He's aware of the fact that there is no absolute system of measurements, and that locations on Earth are always relative to Earth coordinates, not some sort of galactic map. Nitpicking (talk) 14:10, 27 April 2024 (UTC)

Can you be 'once a physicist'? Once you've been a physicist, aren't you always a recovering physicist?172.70.90.92 16:31, 29 April 2024 (UTC)

More immediately, it could not have reasonably happened on Earth, since Earth didn't exist until it happened.172.69.195.3 10:53, 29 April 2024 (UTC)

I wholeheartedly agree. The whole joke, as reinforced by the title text, is that the marker could be anywhere on Earth. Simplify, simplify.DKMell (talk) 16:21, 29 April 2024 (UTC)

Can the Earth's core even have a latitude and a longitude? Aren't those all referring to the surface? --162.158.90.198 11:47, 27 April 2024 (UTC)

You're right. That is the joke, in fact. Nitpicking (talk) 14:10, 27 April 2024 (UTC)

Well, 162.158... is 'right' except that you can indeed have a latitute, longitude and also altitude/depth on top, not just restricting yourself to the surface (or Mean Sea Level or whatever other geometric surface you consider as your default).

As to whether the (centre of the) core can have latitude and longitude, it's a very similar argument as that of whether the (coordinate) poles can have longitudes as well as ±90° latitude.

If you are asking what either pole's longitude is, it would depend upon the what the algorthm was specified (or fails to have been) for the situation, as you could be told 'undefined', 'NaN', given a placeholder constant (e.g. zero), an effectively random value, a value determinate upon what led to this (you were at <location>, 10 miles south of the north pole, and modified that by 10 miles direct northwards travel, so maintain the same longitude as <location> had), a value that would normally be out of range (e.g. for silently passing on, to do the error-catching/checking later on) or several other options.

If you're specifiying the longitude of a pole (for use in an onward algorithm) then it may well (or may not!) be possible to provide any/all of these, but perhaps ultimately ignored/chucked away as meaningless. (Unless you have it doing something like "go ten miles south from north pole, what's the <location> now?", intentionally or otherwise disambiguating via the 'arbitrary but definite' polar longitude.)

So, similarly, if you're asking "What lat/long is the location of the core", the chances are that you're going to get to go through a different manner of deriving a result from that of requesting information such as "This is my lat/long. Is this (above) where the core is?".

...though, yes, this still is very much the joke. Including all the ambiguity as to the rationale involved in however it apparently became disambiguated. 172.69.195.122 21:59, 27 April 2024 (UTC)

It's a valid edit, as it goes, but the reason seems a little over-omniscient. Speaking from another country that does 'signs' quite a bit (for visibility, as well as strategically placed 'table'-style info for closer perusal), I'm not sure we can say it's anywhere near uniquely US-practice. 141.101.99.120 10:28, 29 April 2024 (UTC)

The explanation talks about the impossibly precise date on the sign, but it's not highly precise. It's 4,450,000,000 BCE, which as far as we can tell is precise to the nearest 10 million years, or even 50 million - hardly an exact year. (The precision could have been made clear with scientific notation like 4.45x10⁹, but that's not something you'd put on a sign for the general public.) Rounding to the nearest 10 million years matches the precision of what we know about the formation of the Earth, so it's not unreasonably precise. If Randall had wanted to make a precision joke, he would have used "4,450,002,024 years ago" or something along those lines - something that pegs Earth's formation to a specific year. DKMell (talk) 16:52, 29 April 2024 (UTC)

Firstly, you top-posted. Moved your contribution down here.

Secondly, 4.45x10⁹ only makes clear the imprecision (c.f. "4.450000000x10⁹"). Whereas it would be entirely possible for something to be precisely in the year 4,450,000,000 BCE, as much as it could be 4,450,000,001 BCE or 4,449,999,999 BCE.

Of course you could 'creatively lie' to imply the correct precision (at the expense of the correct accuracy), as in the last paragraph of this section on surveying a certain height... Or you could instead say that it was 4,450,002,023 years ago, but then you'd have to update/replace the sign at some point in 2025. 172.71.242.206 19:49, 29 April 2024 (UTC)

I disagree that "the year 4,450,000,000" is trying to be precise to the nearest 10 million years. In no other context would specifying a single year be understood as saying "give or take a large error." Anthropologists don't claim that agriculture was developed in a certain year, they describe a rough time frame. Randall's choice of giving a precise year, then, is him being overly precise to be funny in an historical marker kind of way. Had he wanted to, he could have had the marker say that the earth formed "4,450,000,000 years ago" and your argument would be correct. He went with the more ridiculous route, and so that impossible precision is appropriately pointed out in the explanation, I think. Laser813 (talk) 19:16, 30 April 2024 (UTC)

Not sure what astronomical standards are inconsistent in this removed text. We can measure (historic) times in terms of a unit exactly 31,557,600 seconds long, the Julian year, even before its establishment. Yet appreciate that a physical (astronomically accurate) solar year at that historic time may be different, especially prior to the Thea-collision which probably did something (could depend upon if Thea had originated from L4 or L5, or what dynamics it possessed if it came from elsewhere), perhaps easily by the requisite amount to build up the nearly 2% difference. Seperately (and unrelated to the actual definition(s) of year), day length has also been changing, thus we know that a physical solar day has been other than 86400 seconds (astronomical day of 86164ish seconds) and a solar year unlikely to have been 365.25 (or 365.2425!) days, so divorcing ephemeris measurements of time (officially 31,556,925.9747 seconds per year in 1900, and changing still) from SI standards of time (as above) is already a thing.
The prior edit removing the Thea-impact-moment idea, I agree more with. Though it does solve the issue of a definitive time and (to some extent) surface location, undoubtedly kicked off the creation of 'nu-Earth' out of the resulting gas and dust and the rest (that didn't get chucked into orbit, to be the Moon, or beyond it to add to the rest of the LHB material). And happened at very much around the time stated by the sign. Given that it's not even supposed to have a real 'answer' to what it means, Thea might well be the answer Randall didn't even think he was leading us to. 172.70.160.173 17:49, 30 April 2024 (UTC)

I concur with the removal that you're questioning, but I also think if you want to put it back in a way that isn't too much of a tangent, go for it. Laser813 (talk) 19:10, 30 April 2024 (UTC)

The mechanism of the Earth's formation is an open area of research. But the general idea is that first, the Sun formed from a collapsing cloud of dust and gas. The remaining dust and gas formed a disk around the Sun called the Sun's protoplanetary disk. From this disk, the planets formed. The best current explanations fall either into the "classical accretion" camp or the "pebble accretion" camp. In classical accretion, dust particles in the Sun's protoplanetary disk collide and coagulate until the resulting body is massive enough to slowly accrete matter through gravitation. In pebble accretion, the dust particles again coagulate to form small pebbles. But here, the pebbles get concentrated in certain parts of the protoplanetary disk where they stick together. This process forms bodies massive enough to accrete matter through gravitation. Neither of those two scenarios involve a collapsing cloud of dust and gas, that's how the Sun formed, not the Earth. Maybe this should be added to the explanation. (I'm new here so I don't what the protocol for proposed changes is.) Source: e.g. https://en.wikipedia.org/wiki/Pebble_accretion Prog (talk) 09:31, 30 July 2024 (UTC)

The protocol is "if you think it's wrong, correct it". Noting that "if other peope think you're wrong, then they'll correct/revert you afterwards" also applies, but I see little to complain about factwise. (Though you might find yourself under pressure to be a bit more summarised than above. I know: I'm also one who'd like to cover every base, every objection, to try not to leave something that's not completely right.)

Note, as you haven't used it here, that we have a "wikilink template", {{w}}, which you'd want to use. Simply do something like {{w|Pebble accretion}} or {{w|Pebble accretion|a process of accreting pebbles}} (the latter gives the link outward text that isn't the wikipage title, if that works better for you). It doesn't do too much different from any of the other ways to linking to wikipedia (though it gets rid of the annoying "locked/unlocked" icon based upon the http(s)ness of the link you would have given), but it reads nicer in the editor than having a full URL, and a bit nicer (YMMV) than [[wikipedia:Article name]] or whatever you might otherwise use. See established edits for general guidance (and use "Show preview" to check such things look ok, rather than have to come back in to edit them right/leave it to someone else to do so). ...otherwise, welcome, new user. You sound like you might fit in rather well, from your attention to detail. 172.69.194.97 11:11, 30 July 2024 (UTC)

Okay, thank you. Let's see what the community thinks about my edit ._. Prog (talk)

-- re: #1, Earth didn't just form at its core, it formed everywhere within its volume. IMO that's the joke - you could put the sign anywhere on Earth and it would be equally valid. It's analogous to putting a sign on Bondi Beach saying "the continent of Australia formed here".

172.68.144.154 02:32, 15 August 2024 (UTC)