Editing 3120: Geologic Periods

{{comic
| number    = 3120
| date      = July 25, 2025
| title     = Geologic Periods
| image     = geologic_periods_2x.png
| imagesize = 611x557px
| noexpand  = true
| titletext = Geologists claim it's because the earlier Cenozoic used to be called the Tertiary, but that's just a ruse to hide the secret third geologic period, between the Neogene and the Quaternary, that they won't tell us about.
}}

==Explanation==
{{incomplete|
*Need more explanation for the entries with birds and raptors: give an explanation similar to the other time periods, and add why he both likes and hates raptors. These are the main jokes in the comic, yet they are not explained at all. Also, were there birds so early? Fixes have been attempted.}}

This comic depicts a table representing planet Earth's geological time scale. The table lists the 12 geological periods of the {{w|Phanerozoic}} Eon plus the time interval from Earth's formation to the start of the Phanerozoic, informally known as the {{w|Precambrian|"Precambrian"}} (see table). The names are listed in chronological order. The first six formal Periods (Cambrian through Permian) belong to the {{w|Palaeozoic}} Era, the next three to the {{w|Mesozoic}} Era, and the final three to the {{w|Cenozoic}} Era. For each period, [[Randall]] has chosen to highlight his rather idiosyncratic likes and dislikes among their characteristics, instead of accompanying each geological name with facts pertinent to it, such as the duration of the period represented, the state of the Earth (e.g. glaciated) during the period, or the flora and fauna most commonly associated with the period. That way the whole setup and style is strongly reminiscent of a typical TV show synopsis in tabular form as could be found at various places on the internet. This may refer to the way that heavily CGI-assisted reconstructions of life in past geological periods are a popular topic for documentary and so-called docutainment shows, which often focus more on entertainment value than the science behind it (hence the term ''docutainment'').

{| class="wikitable"
!Period
!Date range ({{abbr|{{w|Million years ago|MYA}}|Millions of years ago}})
!Randall's favorite part
!Randall's biggest complaint
!Explanation
|-
! {{w|Precambrian}}
|4500&#8288;&#8211;&#8288;539
|Life develops
|Snowball Earth episodes
|The {{w|Precambrian}} (italicized in the comic since it's not a {{w|Period (geology)|geologic period}}) is the first 88% of Earth's history, including the time 4.1 to 3.4 billion years ago when life on Earth began. It's an informal 'catchall' term encompassing the {{w|Hadean}}, {{w|Archaean}}, and {{w|Proterozoic}} Eons that preceded the Phanerozoic. The {{w|Snowball Earth}} hypothesis says that during some time spans in the past, Earth became nearly or entirely frozen, with no liquid water on the surface. This is related to the idea of the {{w|Greenhouse and icehouse Earth#Icehouse Earth|Icehouse Earth}} — times when the planet fluctuates between glacial and interglacial periods (such as now).
|-
! {{w|Cambrian}}
|539&#8288;&#8211;&#8288;487
|Trilobites!
|Evolution could stand to calm down a little
|{{w|Trilobite|Trilobites}}, a lineage of {{w|Arthropod|arthropods}} (related to present-day insects and spiders), was one of the groups that appeared during the Cambrian. Fossil trilobite specimens are abundant and charismatic, due to their distinctive geometric nature, and attract the attention of amateur and professional enthusiasts. The {{w|Cambrian explosion}} was a sudden radiation of complex life forms when nearly all important animal phyla, or precursors to them, appeared.
|-
! {{w|Ordovician}}
|487&#8288;&#8211;&#8288;443
|Earth might have had rings
|Scary volcanic eruption in North America
|Due to the non-random location of impact of one type of meteorite, {{w|Rings of Earth|it is proposed}} that they may have formed a planetary ring system around Earth before colliding with it. The volcanic eruption(s) that deposited the {{w|Deicke and Millbrig bentonite layers}} of ash during the Late Ordovician are thought to have been among the largest in the last 600 million years of Earth history. The volcano(es) involved may have been among those formed during the mountain-building event in what is now north-eastern North America that is called the {{w|Taconic orogeny}}.
|-
! {{w|Silurian}}
|443&#8288;&#8211;&#8288;420
|First land animals
|Earth's newfound mold problem
|Green plants first became established on land during the Ordovician period, after having evolved ways to protect themselves from desiccation and ultraviolet light. During the Silurian, land animals (mostly arthropods resembling {{w|Kampecaris|millipedes}}) followed the plants and mycelial fungi ("mold") evolved to attack them and decompose their remains.
|-
! {{w|Devonian}}
|420&#8288;&#8211;&#8288;359
|Big mountains in Boston
|Yeah, sure, what those giant killer fish needed was ''armor''
|A series of mountain-building events during the middle to late Devonian, collectively termed the {{w|Acadian orogeny}}, resulted in a section of the present-day Appalachian Range from the Canadian maritimes to the Carolinas, including what is now the Boston area of Massachusetts. (At the time, Boston was in the tropics, just south of the equator.) {{w|Placoderm}} fishes, which were common in, but did not survive, the Devonian, were characterized by plates of {{w|dermal bone}} in the head and thoracic portions of the body. Not all placoderms were giants, or apex predators. The best guess as to why placoderm fishes had these bony plates is that they helped protect the fishes from predation by other placoderms.
|-
! {{w|Carboniferous}}
|359&#8288;&#8211;&#8288;299
|Cool forests
|Bugs too big
|Forests in the Carboniferous lacked the flowering plants, cycads, and conifers that dominate present-day forests; flowering plants, in particular, would not appear as fossils in any significant numbers until the Cretaceous, more than 150 million years later. Instead, forests were dominated by giant versions of today's {{w|Lycopodiaceae|club mosses}}, {{w|Equisetidae|horsetails}}, and {{w|Marattiaceae|ferns}}, as well as by several plant lineages that are now extinct. {{w|File:Meyers b15 s0272b.jpg|Artists' depictions}} of such forests are exotic-looking and "cool". The {{w|Carboniferous#Terrestrial invertebrates|'bugs' in this period}} included the largest ever known land invertebrate, a {{w|Arthropleura|2.6 m (8 ft 6 in) millipede-like animal}}; the largest ever known flying insect, resembling a {{w|Meganeura|dragonfly with a wingspan of ~75 cm (2 ft 6 in)}}; and a {{w|Pulmonoscorpius|70 cm (2 ft 4 in) scorpion}}.
|-
! {{w|Permian}}
|299&#8288;&#8211;&#8288;252
|Pangea
|Google "The Great Dying"
|{{w|Pangaea}} was the most recent supercontinent containing nearly all of Earth's landmass. The Great Dying, more formally known as the {{w|Permian-Triassic extinction event}}, occurred at the end of the Permian and is the most severe of Earth's {{w|Extinction event#The "Big Five" mass extinctions|'Big Five' mass extinction events}}. In it, 81% of marine species and 70% of terrestrial vertebrate species were wiped out.
|-
! {{w|Triassic}}
|252&#8288;&#8211;&#8288;201
|Tanystropheus
|Damage to Canada still visible from space at Manicouagan
|''{{w|Tanystropheus}}'' was an {{w|Archosauromorpha|Archosauromorph}} with a proportionally unusually long neck (as depicted in the comic). {{w|Manicouagan Reservoir}} is a ring-shaped lake — the remains of the crater caused by a 5 km (3 mi) asteroid hitting {{w|Quebec}}.
|-
! {{w|Jurassic}}
|201&#8288;&#8211;&#8288;143
|Birds
|Parasitoid wasps
|The {{w|Avialae}}, which were the ancestors of modern birds, emerged during the Jurassic. The reproduction cycle of {{w|parasitoid wasp}}s is such a grisly process, using living animals in which to deposit eggs that then hatch and eat the animal from the inside out, that it caused a {{w|Parasitoid wasp#In culture|crisis of faith}} among 19th-century European scholars.
|-
! {{w|Cretaceous}}
|143&#8288;&#8211;&#8288;66
|Raptors
|Raptors
|The {{w|Dromaeosauridae}} is a lineage of {{w|Paraves|avian dinosaurs}} (see "Avialae", above under "Birds") that first appeared during the Cretaceous. Incorrect reconstructions of the dromaeosaurid genus {{w|Velociraptor|<em>Velociraptor</em>}} feature prominently in the {{w|Velociraptors in Jurassic Park|''Jurassic Park<'' media franchise}}, in which they are major, deadly antagonists of humans. The common name "raptor" derives from <em>Velociraptor</em>. Raptors are a [[:Category:Velociraptors|trope]] within xkcd, especially in its early years. Randall is fascinated by the speed, social behavior, and intelligence of raptors, inferred from fossils and depicted in <em>Jurassic Park</em>, and cringes at their threat to humanity should they appear IRL. Thus, "raptors" appears in both the "Favorites" and "Complaints" columns of the table.
|-
! {{w|Paleogene}}
|66&#8288;&#8211;&#8288;23
|Pretty horseys!!!
|Paleocene-eocene thermal maximum
|Fossils of members of the horse family ({{w|Equidae}}) first appear during this period. Horses, fossil and extant, are prime examples of {{w|charismatic megafauna}} ("Pretty horseys!"). The rapid diversification of horses from a presumed single common ancestor is an oft-cited example of mammalian adaptive radiation in the time period immediately following the {{w|Cretaceous–Paleogene extinction event}}. {{w|Paleocene–Eocene Thermal Maximum}} was a time where the global average temperature rose by 5-8 °C in a relatively short period of time.
|-
! {{w|Neogene}}
|23&#8288;&#8211;&#8288;2.6
|Forests of ''Dracaena'' dragonblood trees
|Zanclean flood
|''{{w|Dracaena draco}}'' and ''{{w|Dracaena cinnabari}}'' trees are a source of {{w|dragon's blood}}, a naturally occurring bright red resin used as a varnish and a dye. The {{w|Zanclean flood}} is theorized to be the flood that refilled the Mediterranean Sea.
|-
! {{w|Quaternary}}
|2.6&#8288;&#8211;&#8288;present
|Burrito invented
|Whoever picked the name for the third period of the Cenozoic
|Randall jokes that, in the last 2.6 million years, his favorite moment was the invention of the {{w|burrito}}, rather than many other, much more significant discoveries. The precise origin of the burrito is not known, but the {{w|Maya civilization}} used to make food resembling burritos as early as 1500 BC.
The third period of the {{w|Cenozoic Era}} is the Quaternary ("Fourth"), named by Jules Desnoyers in 1829. Randall is riffing on the cognitive disconnect between "third" and "fourth", for which the current geological naming conventions offer no explanation.
|}

The title text expands on the complaint about the "third" <em>v</em> "fourth" discrepancy in regard to the Quaternary Period by postulating the existence of an unnamed geologic period within the Cenozoic Era "that geologists won't tell us about". In fact, the use of "Quaternary" (and "Tertiary") in recent/current geological nomenclature is a relic of four centuries of the history of geological studies in Western Europe, complicated by the religiously-inspired acceptance until the beginning of the 19th century, among European scholars, of an Earth that was only 6000 years old. See {{w|Geologic time scale#Formulation of a modern geologic time scale|this summary}} for more details, but briefly, "Primary" rocks were those considered to have been present, in solid formations such as mountains, before the "Great Deluge" of Noah (the {{w|Genesis flood narrative}}), while "Secondary" rocks represented the rubble from the Flood. Igneous and metamorphic rocks came to be understood as "primary", and eldest (within the context of a 6000-year-old Earth), and sedimentary rocks as "secondary". Demonstrably more recent geological formations came to be known as "tertiary" (relatively newer) and "quaternary" (even more recent). As the idea of Earth being billions of years old gained acceptance and tools for accurately dating rocks became available, "primary" and "secondary" fell away as descriptors for both rock types and rock ages, replaced by terms that convey information about the rocks more precisely and accurately. "Tertiary" was applied to "Cenozoic minus Quaternary", and survived in formal nomenclature into the 21st century. No alternative for "Quaternary" has yet been accepted, and so the name persists as fodder for cartoonists who wonder, not without cause, how a "third" element in Earth history could be labeled a "fourth" element.

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

:[A table with 3 columns, labelled: "Period", "My favorite part" and "My biggest complaint". There are 13 rows below the labels]
:[Row 1: Period:] ''Precambrian'' [My favorite part:] Life develops [My biggest complaint:] Snowball Earth episodes
:[Row 2: Period:] Cambrian [My favorite part:] Trilobites! [My biggest complaint:] Evolution could stand to calm down a little
:[Row 3: Period:] Ordovician [My favorite part:] Earth might have had rings [My biggest complaint:] Scary volcanic eruption in North America
:[Row 4: Period:] Silurian [My favorite part:] First land animals [My biggest complaint:] Earth's newfound mold problem
:[Row 5: Period:] Devonian [My favorite part:] Big mountains in Boston [My biggest complaint:] Yeah, sure, what those giant killer fish needed was '''''armor'''''
:[Row 6: Period:] Carboniferous [My favorite part:] Cool forests [My biggest complaint:] Bugs too big
:[Row 7: Period:] Permian [My favorite part:] Pangea [My biggest complaint:] Google "The Great Dying"
:[Row 8: Period:] Triassic [My favorite part:] Tanystropheus [accompanying the text in this cell is an image of a ''Tanystropheus'' and its characteristic elongated neck, with Cueball standing next to it for scale] [My biggest complaint:] Damage to Canada still visible from space at Manicouagan
:[Row 9: Period:] Jurassic [My favorite part:] Birds [My biggest complaint:] Parasitoid wasps
:[Row 10: Period:] Cretaceous [My favorite part:] Raptors [My biggest complaint:] Raptors
:[Row 11: Period:] Paleogene [My favorite part:] Pretty horseys!!! [My biggest complaint:] Paleocene-eocene thermal maximum
:[Row 12: Period:] Neogene [My favorite part:] Forests of ''Dracaena'' dragonblood trees [My biggest complaint:] Zanclean flood
:[Row 13: Period:] Quaternary [My favorite part:] Burrito invented [My biggest complaint:] Whoever picked the name for the third period of the Cenozoic

{{comic discussion}}<noinclude>
[[Category:Charts]]
[[Category:Geology]]
[[Category:Velociraptors]]
[[Category:Animals]]
[[Category:Food]]
[[Category:Comics featuring Cueball]]