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| Geologic Periods |
 Title text: 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
| Period | Date range (MYA) | Randall's favorite part | Randall's biggest complaint | Explanation |
|---|---|---|---|---|
| Precambrian | 4500–539 | Life develops | Snowball Earth episodes | The Precambrian (italicized in the comic since it's not a 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 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 icehouse Earth, times when the planet fluctuates between glacial and interglacial periods (such as now). |
| Cambrian | 539–487 | Trilobites! | Evolution could stand to calm down a little | The Cambrian explosion was a sudden radiation of complex life forms when nearly all important animal phyla, or precursors to them, appeared. Trilobites, a lineage of 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, and attract the attention of amateur and professional enthusiasts. |
| Ordovician | 487–443 | Earth might have had rings | Scary volcanic eruption in North America | Due to the non-random location of impact of one type of meteorite, it is proposed that those have formed a planetary ring system around Earth before colliding with it. The volcanic eruption(s) that deposited the Deicke and Millbrig ashfall layers 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 northeastern North America that is called the Taconic orogeny. |
| Silurian | 443–420 | 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 millipedes) followed the plants and mycelial fungi ("mold") evolved to attack them and decompose their remains. |
| Devonian | 420–359 | 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, that are collectively termed the 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.) Placoderm fishes, which were common in but did not survive the Devonian, were characterized by plates of 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. |
| Carboniferous | 359–299 | Cool forests | Bugs too big | The 'bugs' in this period included the largest-ever known land invertebrate, a 2.6 m (8.5 ft) millipede-like animal; the largest-ever known flying insect, resembling a dragonfly with a wingspan of ~75 cm (30 in); and a 70 cm (2 ft 4 in) scorpion. |
| Permian | 299–252 | Pangea | Google "The Great Dying" | Pangaea was the most recent supercontinent containing nearly all of Earth's landmass. The Great Dying, more formally known as the Permian-Triassic extinction event, occurred at the end of the Permian and is the most severe of Earth's 'Big Five' mass extinction events. In it, 81% of marine species and 70% of terrestrial vertebrate species were wiped out. |
| Triassic | 252–201 | Tanystropheus | Damage to Canada still visible from space at Manicouagan | Tanystropheus was a basal archosaur (not a dinosaur) with a disproportionally long neck. Manicouagan Reservoir is a ring-shaped lake, the remains of the crater caused by a 5 km (3 mi) asteroid hitting Quebec. |
| Jurassic | 201–143 | Birds | Parasitoid wasps | Birds are cool.[citation needed] Parasitoid wasps are not; their reproduction cycle is such a grisly process that it caused a crisis of faith among 19th-century European scholars. |
| Cretaceous | 143–66 | Raptors | Raptors | Raptors |
| Paleogene | 66–23 | Pretty horseys!!! | Paleocene-eocene thermal maximum | The Paleocene–Eocene Thermal Maximum was a time where the global average temperature rose by around 5-8 °C in a relatively short period of time. |
| Neogene | 23–2.6 | Forests of Dracaena dragonblood trees | Zanclean flood | Dracaena draco and Dracaena cinnabari trees are a source of dragon's blood, a naturally occurring bright red resin with uses including as a varnish and a dye. The Zanclean flood is theorized to be the flood that refilled the Mediterranean Sea. |
| Quaternary | 2.6–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 burrito, rather than many other, much more significant discoveries. The precise origin of the burrito is not known, but the Maya civilization used to make food resembling burritos as early as 1500 BC. The third period of the Cenozoic Era is the Quaternary era, named by Jules Desnoyers in 1829. This naming is controversial; the International Commission on Stratigraphy is proposing to abolish it. |
Transcript
- [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
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