https://www.explainxkcd.com/wiki/api.php?action=feedcontributions&feedformat=atom&user=2A01%3AE0A%3A1F4%3A9050%3A253D%3A7854%3AF4AD%3A6DB3explain xkcd - User contributions [en]2026-05-22T20:34:56ZUser contributionsMediaWiki 1.30.0https://www.explainxkcd.com/wiki/index.php?title=3120:_Geologic_Periods&diff=3819663120: Geologic Periods2025-07-26T13:27:55Z<p>2A01:E0A:1F4:9050:253D:7854:F4AD:6DB3: rings</p>
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<div>{{comic<br />
| number = 3120<br />
| date = July 25, 2025<br />
| title = Geologic Periods<br />
| image = geologic_periods_2x.png<br />
| imagesize = 611x557px<br />
| noexpand = true<br />
| 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.<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|This page was created by a Cretaceous raptor. Don't remove this notice too soon.}}<br />
<br />
{| class="wikitable"<br />
!Period<br />
!Dates (millions of years ago)<br />
!My Favorite Part<br />
!My Biggest Complaint<br />
!Explanation<br />
|-<br />
|Precambrian<br />
|4500-539<br />
|Life develops<br />
|Snowball Earth episodes<br />
|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. 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. It's 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).<br />
|-<br />
|{{w|Cambrian}}<br />
|539-487<br />
|Trilobites!<br />
|Evolution could stand to calm down a little<br />
|The {{w|Cambrian explosion}} was a sudden radiation of complex life forms when nearly all important animal phyla, or precursors to them, appeared.<br />
|-<br />
|{{w|Ordovician}}<br />
|487-443<br />
|Earth might have had rings<br />
|Scary volcanic eruption in North America<br />
|Due to the non-random location of impact of one type of meteorite, {{w|https://en.wikipedia.org/wiki/Rings_of_Earth|it is proposed}} that those have formed a planetary ring system around Earth before colliding with it. <br />
|-<br />
|{{w|Silurian}}<br />
|443-420<br />
|First land animals<br />
|Earth's newfound mold problem<br />
|<br />
|-<br />
|{{w|Devonian}}<br />
|420-359<br />
|Big mountains in Boston<br />
|Yeah, sure, what those giant killer fish needed was armor<br />
|<br />
|-<br />
|{{w|Carboniferous}}<br />
|359-299<br />
|Cool forests<br />
|Bugs too big<br />
|The {{w|Carboniferous#Terrestrial_invertebrates|'bugs' in this period}} included the largest-ever known land invertebrate, a {{w|Arthropleura|2.6-m (8.5-ft) millipede-like animal}}; the largest-ever known flying insect, resembling a {{w|Meganeura|dragonfly with a wingspan of ~75 cm (30 in)}}; and a {{w|Pulmonoscorpius|70 cm (2 ft 4 in) scorpion}}.<br />
|-<br />
|{{w|Permian}}<br />
|299-252<br />
|Pangea<br />
|Google "The Great Dying"<br />
|{{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.<br />
|-<br />
|{{w|Triassic}}<br />
|252-201<br />
|Tanystropheus<br />
|Damage to Canada still visible from space at Manicouagan<br />
|{{w|Tanystropheus}} was a basal archosaur (not a dinosaur) with a proportionally long neck. {{w|Manicouagan Reservoir}} is a ring-shaped lake, the remains of the crater caused by a 5-km (3-mi) asteroid hitting {{w|Quebec}}.<br />
|-<br />
|{{w|Jurassic}}<br />
|201-143<br />
|Birds<br />
|Parasitoid wasps<br />
|Birds are cool{{Citation needed}}. Parasitoid wasps are not; their reproduction cycle is such a grisly process that it caused a {{w|Ichneumonidae#Darwin_and_the_Ichneumonidae|crisis of faith}} among 19th-century European scholars.<br />
|-<br />
|{{w|Cretaceous}}<br />
|143-66<br />
|Raptors<br />
|Raptors<br />
|[[:Category:Velociraptors|Raptors]]<br />
|-<br />
|{{w|Paleogene}}<br />
|66-23<br />
|Pretty horseys!!!<br />
|Paleocene-eocene thermal maximum<br />
|The {{w|Paleocene–Eocene Thermal Maximum}} was a time where the global average temperature rose by around 5-8 °C is a relatively short period of time.<br />
|-<br />
|{{w|Neogene}}<br />
|23-2.6<br />
|Forests of Dracaena dragonblood trees<br />
|Zanclean flood<br />
|The {{w|Zanclean flood}} is theorized to be the flood that refilled the Mediterranean Sea.<br />
|-<br />
|{{w|Quaternary}}<br />
|2.6-present<br />
|Burrito invented<br />
|Whoever picked the name for the third period of the Cenozoic<br />
|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.<br />
The third period of the {{w|Cenozoic}} Era is the Quaternary era, named by Jules Desnoyers in 1829. This naming is controversial, as the {{w|International Commission on Stratigraphy}} is proposing to abolish it.<br />
|}<br />
<br />
==Transcript==<br />
{{incomplete transcript|Don't remove this notice too soon.}}<br />
<br />
{{comic discussion}}<noinclude><br />
[[Category:Charts]]<br />
[[Category:Geology]]<br />
[[Category:Velociraptors]]<br />
[[Category:Animals]]<br />
[[Category:Food]]<br />
[[Category:Comics featuring Cueball]]</div>2A01:E0A:1F4:9050:253D:7854:F4AD:6DB3