I took notes on the following because I was curious about the terms Jurassic and Cretaceous, and that led me down a rabbit hole.
mya: acronym for "million years ago"
Ma: abbreviation for megaannum, a unit representing one million years
The following are defined by the International Commission on Stratigraphy.
Eon: Half a billion years or more
Era: Several hundred million years
Period: Tens to about a hundred million years
Epoch: Tens of millions of years
Age: Millions of years
Phanerozoic: 538 mya to present day
Proterozoic: 2,500 mya to 538 mya
Archean: 4,031 mya to 2,500 mya
Hadean: 4,567.3 mya to 4,031 mya
Cenozoic: 66 mya to present day
Mesozoic: 251.9 mya to 66 mya
Paleozoic: 538.8 mya to 251.9 mya
Neoproterozoic: 1,000 mya to 538.8 mya
Mesoproterozoic: 1,600 mya to 1,000 mya
Paleoproterozoic: 2,500 mya to 1,600 mya
Neoarchean: 2,800 mya to 2,500 mya
Mesoarchean: 3,200 mya to 2,800 mya
Paleoarchean: 3,600 mya to 3,200 mya
Eoarchean: 4,031 mya to 3,600 mya
Quaternary: 2.6 mya to present day
Neogene: 23 mya to 2.6 mya
Paleogene: 66 mya to 23 mya
Cretaceous: 146 mya to 66 mya
Jurassic: 201.4 mya to 146 mya
Triassic: 251.9 mya to 201.4 mya
Permian: 298.9 mya to 251.9 mya
Carboniferous: 358.9 mya to 298.9 mya
Devonian: 419.2 mya to 358.9 mya
Silurian: 443.8 mya to 419.2 mya
Ordovician: 485.4 mya to 443.8 mya
Cambrian: 538.8 mya to 485.4 mya
Ediacaran: 635 mya to 538.8 mya
Cryogenian: 720 mya to 635 mya
Tonian: 1,000 mya to 720 mya
Stenian: 1,200 mya to 1,000 mya
Ectasian: 1,400 mya to 1,200 mya
Calymmian: 1,600 mya to 1,400 mya
Statherian: 1,800 mya to 1,600 mya
Orosirian: 2,050 mya to 1,800 mya
Rhyacin: 2,300 mya to 2,050 mya
Siderian: 2,500 mya to 2,300 mya
Holocene: 0.012 mya to present day
Pleistocene: 2.58 mya to 0.012 mya
Pliocene: 5.33 mya to 2.58 mya
Miocene: 23.03 mya to 5.33 mya
Oligocene: 33.9 mya to 23.03 mya
Eocene: 56 mya to 33.9 mya
Paleocene: 66 mya to 56 mya
Upper Cretaceous: 100.5 mya to 66 mya
Lower Cretaceous: 145 mya to 100.5 mya
Upper Jurassic: 161.5 mya to 145 mya
Middle Jurassic: 174.7 mya to 161.5 mya
Lower Jurassic: 201.4 mya to 174.7 mya
Upper Triassic: 237 mya to 201.4 mya
Middle Triassic: 247.2 mya to 237 mya
Lower Triassic: 251.9 mya to 247.2 mya
Lopingian: 259.51 mya to 251.9 mya
Guadalupian: 273.01 mya to 259.51 mya
Cisuralian: 298.9 mya to 273.01 mya
Upper Pennsylvanian: 307 mya to 298.9 mya
Middle Pennsylvanian: 315.2 mya to 307 mya
Lower Pennsylvanian: 323.2 mya to 315.2 mya
Upper Mississippian: 330.9 mya to 323.2 mya
Middle Mississippian: 346.7 mya to 330.9 mya
Lower Mississippian: 358.9 mya to 346.7 mya
Upper Devonian: 382.7 mya to 358.9 mya
Middle Devonian: 393.3 mya to 382.7 mya
Lower Devonian: 419.2 mya to 393.3 mya
Pridoli: 423 mya to 419.2 mya
Ludlow: 427.4 mya to 423 mya
Wenlock: 433.3 mya to 427.4 mya
Llandovery: 443.8 mya to 433.4 mya
Upper Ordovician: 458.4 mya to 443.8 mya
Middle Ordovician: 470 mya to 458.4 mya
Lower Ordovician: 485.4 mya to 470 mya
Furongian: 497 mya to 485.4 mya
Miaolingian: 509 mya to 497 mya
Cambrian Series 2: 521 mya to 509 mya
Terreneuvian: 538.8 mya to 521 mya