3243: Crystal Gazing - Revision history

2603:6011:1F0:2A40:C522:C804:9042:7B68: /* Explanation */

2026-05-15T00:31:59Z

‎Explanation

Machina Lucis: Change to more technical terms

2026-05-13T14:08:56Z

Change to more technical terms

RG at 02:17, 13 May 2026

2026-05-13T02:17:47Z

2603:6011:1F0:2A40:C5FD:DD48:3894:40A2 at 23:06, 12 May 2026

2026-05-12T23:06:02Z

2603:6011:1F0:2A40:C5FD:DD48:3894:40A2 at 23:03, 12 May 2026

2026-05-12T23:03:48Z

82.13.184.33: /* Explanation */

2026-05-12T08:15:09Z

‎Explanation

82.13.184.33: /* Explanation */

2026-05-12T08:12:27Z

‎Explanation

82.13.184.33: /* Explanation */

2026-05-12T08:11:22Z

‎Explanation

DKMell: what is a geochronologist

2026-05-11T21:50:38Z

what is a geochronologist

216.51.189.93: /* Explanation */

2026-05-11T20:24:03Z

‎Explanation

@@ Line 10: / Line 10: @@
 ==Explanation==
-A {{w|geochronology|geochronologist}} (someone who estimates the ages of rocks, fossils, etc.)  dressed up as a wizard (assuming that isn't how they normally dress) announces &mdash; in archaic language befitting his costume &mdash; that he has determined the {{w|age of the Earth}} by analyzing {{w|zircon}}. Zircon is a crystal with the formula ZrSiO<sub>4</sub>. During its formation it can incorporate uranium instead of zirconium in its crystal lattice, but cannot incorporate lead. The uranium then decays (via several intermediates) into lead. Thus a sufficiently old zircon crystal will contain some lead, allowing geologists to {{w|Detrital_zircon_geochronology|calculate its age}}. This method is especially reliable, since uranium-238 decays into lead-206 with a half-life of 4.5 billion years, while uranium-235 decays into lead-207 with a half-life of 0.7 billion years, allowing geologists to determine the age even where some lead was lost from the crystal. The geochronologist says he predicted the age of the Earth by gazing into the crystal, similar to the traditional fortune tellers' method of making predictions by gazing into crystal balls.
+A {{w|geochronology|geochronologist}} (someone who estimates the ages of rocks, fossils, etc.)  dressed up as a wizard (assuming that isn't how they normally dress) announces &mdash; in archaic language befitting his costume &mdash; that he has determined the {{w|age of the Earth}} by analyzing {{w|zircon}}. Zircon is a crystal with the formula ZrSiO<sub>4</sub>. During its formation it can incorporate uranium instead of zirconium in its crystal lattice, but cannot incorporate lead. The uranium then decays (via several intermediates) into lead. Thus a sufficiently old zircon crystal will contain some lead, allowing geologists to {{w|Detrital_zircon_geochronology|calculate its age}}. This method is especially reliable, since uranium-238 decays into lead-206 with a half-life of 4.5 billion years, while uranium-235 decays into lead-207 with a half-life of 0.7 billion years, allowing geologists to determine the age even where some lead was lost from the crystal. The geochronologist says he predicted the age of the Earth by gazing into the [[2776|crystal]], similar to the traditional fortune tellers' method of making predictions by gazing into crystal balls.
 A prophet of doom is someone who predicts impending disasters, particularly the end of the world (and there are lots of ridiculous ways that [https://what-if.xkcd.com/archive/ could happen]). These prophets and predictions are especially common in fantasy media. The joke in the caption is that someone who can determine when the world began is just doing this in reverse, and that's what geochronologists are doing when they calculate the age of the Earth. His last line, "the beginning was nigh", is a reversal of the phrase stereotypically used by prophets of doom: "the end is nigh". This is in keeping with the idea represented in the comic.

@@ Line 14: / Line 14: @@
 A prophet of doom is someone who predicts impending disasters, particularly the end of the world (and there are lots of ridiculous ways that [https://what-if.xkcd.com/archive/ could happen]). These prophets and predictions are especially common in fantasy media. The joke in the caption is that someone who can determine when the world began is just doing this in reverse, and that's what geochronologists are doing when they calculate the age of the Earth. His last line, "the beginning was nigh", is a reversal of the phrase stereotypically used by prophets of doom: "the end is nigh". This is in keeping with the idea represented in the comic.
-The title text points out, in similar flowery language (in keeping with the character being a wizard from a {{w|J. R. R. Tolkien|Tolkienesque}} or {{w|Dungeons & Dragons}}-type world, where [https://tolkiengateway.net/wiki/Vales_of_Anduin vales] are often part of the geographical language), that many areas of physical sciences have a limiting horizon to their ability to study their subject. {{w|Geologists}} are limited by the early molten history of the Earth, in that most of the crust has been recycled back into the molten mantle at some point, and the mantle acts as a physical 'vale of fire' for the core — each limiting what can be studied. Similarly, {{w|heliophysicists}} have difficulty knowing what happens within the Sun due to the physical 'vale of fire' that is the Sun's surface. Finally, {{w|cosmologists}} have difficulty studying beyond the {{w|recombination (cosmology)|'recombination' era}}, beyond which the universe is shielded by a 'vale of fire' ({{w|cosmic microwave background}}) from electromagnetic observation — both in time (investigating the early universe) or in space (investigating beyond the event horizon of the visible universe).
+The title text points out, in similar flowery language (in keeping with the character being a wizard from a {{w|J. R. R. Tolkien|Tolkienesque}} or {{w|Dungeons & Dragons}}-type world, where [https://tolkiengateway.net/wiki/Vales_of_Anduin vales] are often part of the geographical language), that many areas of physical sciences have a limiting horizon to their ability to study their subject. {{w|Geologists}} are limited by the early molten history of the Earth, in that most of the crust has been recycled back into the molten mantle at some point, and the mantle acts as a physical 'vale of fire' for the core — each limiting what can be studied. Similarly, {{w|heliophysicists}} have difficulty knowing what happens within the Sun due to the physical 'vale of fire' that is the Sun's {{w|photosphere}}. Finally, {{w|cosmologists}} have difficulty studying the universe beyond the {{w|recombination (cosmology)|recombination epoch}}, beyond which the universe is shielded by a 'vale of fire' (the {{w|surface of last scattering }} from which photons of the {{w|cosmic microwave background}} escape) from electromagnetic observation — both in time (investigating the early universe) or in space (investigating beyond the event horizon of the visible universe).
 [[:Category:Dungeons & Dragons|D&D]] is a recurring topic on xkcd.

← Older revision		Revision as of 02:17, 13 May 2026
Line 19:		Line 19:

	==Transcript==		==Transcript==
−	~~{{incomplete transcript\|Don't remove this notice too soon.}}~~

	:[A character in wizard garb with long beard and hair talks to Cueball. To the left of the wizard is a poster with illegible text over a graph with two lines intersecting.]		:[A character in wizard garb with long beard and hair talks to Cueball. To the left of the wizard is a poster with illegible text over a graph with two lines intersecting.]

@@ Line 9: / Line 9: @@
 }}
+==Explanation==
 A {{w|geochronology|geochronologist}} (someone who estimates the ages of rocks, fossils, etc.)  dressed up as a wizard (assuming that isn't how they normally dress) announces &mdash; in archaic language befitting his costume &mdash; that he has determined the {{w|age of the Earth}} by analyzing {{w|zircon}}. Zircon is a crystal with the formula ZrSiO<sub>4</sub>. During its formation it can incorporate uranium instead of zirconium in its crystal lattice, but cannot incorporate lead. The uranium then decays (via several intermediates) into lead. Thus a sufficiently old zircon crystal will contain some lead, allowing geologists to {{w|Detrital_zircon_geochronology|calculate its age}}. This method is especially reliable, since uranium-238 decays into lead-206 with a half-life of 4.5 billion years, while uranium-235 decays into lead-207 with a half-life of 0.7 billion years, allowing geologists to determine the age even where some lead was lost from the crystal. The geochronologist says he predicted the age of the Earth by gazing into the crystal, similar to the traditional fortune tellers' method of making predictions by gazing into crystal balls.

← Older revision		Revision as of 23:03, 12 May 2026
Line 9:		Line 9:
	}}		}}

−	~~==Explanation==~~
−	~~{{incomplete\|This page was created over 4.547 nanoseconds ago. Don't remove this notice too soon.}}~~

	A {{w\|geochronology\|geochronologist}} (someone who estimates the ages of rocks, fossils, etc.) dressed up as a wizard (assuming that isn't how they normally dress) announces — in archaic language befitting his costume — that he has determined the {{w\|age of the Earth}} by analyzing {{w\|zircon}}. Zircon is a crystal with the formula ZrSiO<sub>4</sub>. During its formation it can incorporate uranium instead of zirconium in its crystal lattice, but cannot incorporate lead. The uranium then decays (via several intermediates) into lead. Thus a sufficiently old zircon crystal will contain some lead, allowing geologists to {{w\|Detrital_zircon_geochronology\|calculate its age}}. This method is especially reliable, since uranium-238 decays into lead-206 with a half-life of 4.5 billion years, while uranium-235 decays into lead-207 with a half-life of 0.7 billion years, allowing geologists to determine the age even where some lead was lost from the crystal. The geochronologist says he predicted the age of the Earth by gazing into the crystal, similar to the traditional fortune tellers' method of making predictions by gazing into crystal balls.		A {{w\|geochronology\|geochronologist}} (someone who estimates the ages of rocks, fossils, etc.) dressed up as a wizard (assuming that isn't how they normally dress) announces — in archaic language befitting his costume — that he has determined the {{w\|age of the Earth}} by analyzing {{w\|zircon}}. Zircon is a crystal with the formula ZrSiO<sub>4</sub>. During its formation it can incorporate uranium instead of zirconium in its crystal lattice, but cannot incorporate lead. The uranium then decays (via several intermediates) into lead. Thus a sufficiently old zircon crystal will contain some lead, allowing geologists to {{w\|Detrital_zircon_geochronology\|calculate its age}}. This method is especially reliable, since uranium-238 decays into lead-206 with a half-life of 4.5 billion years, while uranium-235 decays into lead-207 with a half-life of 0.7 billion years, allowing geologists to determine the age even where some lead was lost from the crystal. The geochronologist says he predicted the age of the Earth by gazing into the crystal, similar to the traditional fortune tellers' method of making predictions by gazing into crystal balls.

@@ Line 16: / Line 16: @@
 A prophet of doom is someone who predicts impending disasters, particularly the end of the world (and there are lots of ridiculous ways that [https://what-if.xkcd.com/archive/ could happen]). These prophets and predictions are especially common in fantasy media. The joke in the caption is that someone who can determine when the world began is just doing this in reverse, and that's what geochronologists are doing when they calculate the age of the Earth. His last line, "the beginning was nigh", is a reversal of the phrase stereotypically used by prophets of doom: "the end is nigh". This is in keeping with the idea represented in the comic.
-An alternate explanation to this comic is that the geologist is a {{w|Dungeons & Dragons}}-type wizard. [[:Category:Dungeons & Dragons|D&D]] is a recurring topic on xkcd, and given some D&D games shown, a wizard geologist (geomancer class) would be no surprise to see! However, the specific qualities of the wizard shown are not exclusive to D&D, and the same depiction pops up in many places.
+The title text points out, in similar flowery language (in keeping with the character being a wizard from a {{w|J. R. R. Tolkien|Tolkienesque}} or {{w|Dungeons & Dragons}}-type world, where [https://tolkiengateway.net/wiki/Vales_of_Anduin vales] are often part of the geographical language), that many areas of physical sciences have a limiting horizon to their ability to study their subject. {{w|Geologists}} are limited by the early molten history of the Earth, in that most of the crust has been recycled back into the molten mantle at some point, and the mantle acts as a physical 'vale of fire' for the core — each limiting what can be studied. Similarly, {{w|heliophysicists}} have difficulty knowing what happens within the Sun due to the physical 'vale of fire' that is the Sun's surface. Finally, {{w|cosmologists}} have difficulty studying beyond the {{w|recombination (cosmology)|'recombination' era}}, beyond which the universe is shielded by a 'vale of fire' ({{w|cosmic microwave background}}) from electromagnetic observation — both in time (investigating the early universe) or in space (investigating beyond the event horizon of the visible universe).
-The title text points out, in similar flowery language (in keeping with the character being a wizard from a {{w|J. R. R. Tolkien|Tolkienesque}} world, where [https://tolkiengateway.net/wiki/Vales_of_Anduin vales] are often part of the geographical language), that many areas of physical sciences have a limiting horizon to their ability to study their subject. {{w|Geologists}} are limited by the early molten history of the Earth, in that most of the crust has been recycled back into the molten mantle at some point, and the mantle acts as a physical 'vale of fire' for the core — each limiting what can be studied. Similarly, {{w|heliophysicists}} have difficulty knowing what happens within the Sun due to the physical 'vale of fire' that is the Sun's surface. Finally, {{w|cosmologists}} have difficulty studying beyond the {{w|recombination (cosmology)|'recombination' era}}, beyond which the universe is shielded by a 'vale of fire' ({{w|cosmic microwave background}}) from electromagnetic observation — both in time (investigating the early universe) or in space (investigating beyond the event horizon of the visible universe).
+[[:Category:Dungeons & Dragons|D&D]] is a recurring topic on xkcd.
 ==Transcript==

@@ Line 12: / Line 12: @@
 {{incomplete|This page was created over 4.547 nanoseconds ago. Don't remove this notice too soon.}}
-A geologist dressed up as a wizard (assuming that isn't how they normally dress) announces &mdash; in archaic language befitting his costume &mdash; that he has determined the {{w|age of the Earth}} by analyzing {{w|zircon}}. Zircon is a crystal with the formula ZrSiO<sub>4</sub>. During its formation it can incorporate uranium instead of zirconium in its crystal lattice, but cannot incorporate lead. The uranium then decays (via several intermediates) into lead. Thus a sufficiently old zircon crystal will contain some lead, allowing geologists to {{w|Detrital_zircon_geochronology|calculate its age}}. This method is especially reliable, since uranium-238 decays into lead-206 with a half-life of 4.5 billion years, while uranium-235 decays into lead-207 with a half-life of 0.7 billion years, allowing geologists to determine the age even where some lead was lost from the crystal. The {{w|geochronology|geochronologist}} — someone who estimates the ages of rocks, fossils, etc. — says he predicted the age of the Earth by gazing into the crystal, similar to how fortune tellers traditionally make predictions by gazing into crystal balls.
+A {{w|geochronology|geochronologist}} (someone who estimates the ages of rocks, fossils, etc.)  dressed up as a wizard (assuming that isn't how they normally dress) announces &mdash; in archaic language befitting his costume &mdash; that he has determined the {{w|age of the Earth}} by analyzing {{w|zircon}}. Zircon is a crystal with the formula ZrSiO<sub>4</sub>. During its formation it can incorporate uranium instead of zirconium in its crystal lattice, but cannot incorporate lead. The uranium then decays (via several intermediates) into lead. Thus a sufficiently old zircon crystal will contain some lead, allowing geologists to {{w|Detrital_zircon_geochronology|calculate its age}}. This method is especially reliable, since uranium-238 decays into lead-206 with a half-life of 4.5 billion years, while uranium-235 decays into lead-207 with a half-life of 0.7 billion years, allowing geologists to determine the age even where some lead was lost from the crystal. The geochronologist says he predicted the age of the Earth by gazing into the crystal, similar to the traditional fortune tellers' method of making predictions by gazing into crystal balls.
 A prophet of doom is someone who predicts impending disasters, especially the end of the world (and there are lots of ridiculous ways that [https://what-if.xkcd.com/archive/ could happen].) These prophets and predictions are especially common in fantasy media. The joke in the caption is that someone who can determine when the world began is just doing this in reverse, and that's what geochronologists are doing when they calculate the age of the Earth. His last line, "the beginning was nigh", is a reversal of the phrase stereotypically used by prophets of doom: "the end is nigh". This is in keeping with the idea represented in the comic.