3120: Geologic Periods

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Period	Dates (millions of years ago)	My Favorite Part	My 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 proportionally 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.