All 29 Geologic Time Scale flashcards. Free.
The whole deck, not a sample — Geologic Time Scale is 29 cards, which is no longer than the 30 we give away on every deck, so there is nothing left to charge for. 13 pages, US Letter, black and white. Grades 8–12.
No account, no email, no card details.
13 pages, and the backs are already right
Every front sheet is followed by its own back sheet with the rows reversed. Print double-sided, flip on the long edge, and answer number 7 is behind question number 7. Print a deck you built yourself, flip on the short edge, and every answer lands on the wrong card — which nobody finds out until sixty cards have been cut apart.
- 29 cards — counted out of the file, not rounded up
- Eight cards a sheet, with cut guides
- US Letter PDF, black and white, photocopier-friendly
- Print a set per student, every class, every year
29 cards. The chart has a canonical shape: 4 eons, 3 Phanerozoic eras, 12 Phanerozoic periods and the 2 Neoproterozoic periods a school course names, plus the Cenozoic epochs and the six rules you need to read the chart at all. Adding the stage level would more than triple that without teaching anything a course asks for.
Every card here is cited to two independent sources
Two different organisations — not a standards body and a website reprinting it — and a script refuses the card if the two disagree, so the check runs on every card rather than on the ones somebody remembered to look at. A second specialist then re-verified this deck from sources of their own, without reading our citations first. A further 5,420 cards across 30 other decks were read end to end by a subject specialist instead, and we say which is which on every deck rather than averaging the two into one flattering word.
What 29 printed cards do that a screen does not
A phone deck is one card at a time. A printed deck is a pile you can split: the ones you know, the ones you nearly know, and the ones you keep missing. That third pile is the entire study session, and it is the thing a scrolling app hides from you.
- Print once, use all year. The licence covers a set per student, every class, every year.
- No device, no login, no data. Works in a cover lesson, on a bus, or at a kitchen table. Grades 8–12, filed under science.
- Change what you disagree with. Every card loads into the free maker on this site. Reword it, drop it, add your own, reprint.
Here are all 29 cards
Check them against your own textbook before you spend anything.
- The ranks of geologic time, longest to shortest
- Eon → era → period → epoch → age (the rock-body names are eonothem, erathem, system, series, stage)
- GSSP, the 'golden spike'
- A fixed point in a named rock section that defines a boundary. The age in Ma is an estimate; the spike is the definition
- Do the boundary dates change?
- Yes. Only GSSPs define boundaries; the ages are re-dated — the base of the Cretaceous moved from 145.0 to 143.1 Ma
- Is 'Tertiary' still a period?
- Not on the ICS chart — Paleogene and Neogene replaced it. USGS still allows T on US maps but urges the new names
- Is the Anthropocene an epoch?
- No — the ICS Quaternary subcommission rejected the proposal and IUGS approved that rejection, 20 March 2024
- Precambrian
- An informal term with no stratigraphic rank — everything before the Cambrian: the Hadean, Archean and Proterozoic
- Hadean Eon
- About 4567 to 4031 Ma — a formal eon since 2022; accretion, the Moon-forming impact, no surviving rock record
- Archean Eon
- 4031 to 2500 Ma — the oldest surviving rocks and the first known life, under an atmosphere with no free oxygen
- Proterozoic Eon
- 2500 to 538.8 Ma — oxygen builds up in the air, eukaryotes appear, and Snowball Earth glaciations strike
- Phanerozoic Eon
- 538.8 Ma to now — the eon of 'visible life', when fossils become abundant; Paleozoic, Mesozoic, Cenozoic
- Paleozoic Era
- 538.8 to 251.902 Ma — Cambrian to Permian; life colonises the land, and it ends in the largest known extinction
- Mesozoic Era
- 251.902 to 66.0 Ma — Triassic, Jurassic, Cretaceous; the age of dinosaurs, ended by the K–Pg impact
- Cenozoic Era
- 66.0 Ma to now — Paleogene, Neogene, Quaternary; mammals radiate into the niches left vacant by the K–Pg
- Cryogenian Period
- About 720 to 635 Ma — the Sturtian and Marinoan glaciations, the 'Snowball Earth' episodes
- Ediacaran Period
- About 635 to 538.8 Ma — the last Proterozoic period; soft-bodied Ediacaran biota before the Cambrian
- Cambrian Period
- 538.8 to 486.85 Ma — first period of the Paleozoic; the Cambrian explosion, when most animal phyla appear
- Ordovician Period
- 486.85 to 443.1 Ma — great marine radiation and the first land plants; ends in glaciation and mass extinction
- Silurian Period
- 443.1 to 419.62 Ma — sea level rebounds after the ice; reefs, jawed fishes, vascular plants on the coasts
- Devonian Period
- 419.62 to 358.86 Ma — the Age of Fishes; the first in-place forests and the first tetrapods; late extinctions
- Carboniferous Period
- 358.86 to 298.9 Ma — coal-forming swamps and giant insects; split into the Mississippian and Pennsylvanian subperiods
- Permian Period
- 298.9 to 251.902 Ma — Pangaea assembled; ends in the largest known extinction, most estimates 80–90% of species
- Triassic Period
- 251.902 to 201.4 Ma — recovery from the great dying; the first dinosaurs and the first mammals appear
- Jurassic Period
- 201.4 to 143.1 Ma — Pangaea breaks apart; dinosaurs dominant; Archaeopteryx, the earliest known bird
- Cretaceous Period
- 143.1 to 66.0 Ma — flowering plants spread and seas stand high; ends with the K–Pg impact extinction
- Paleogene Period
- 66.0 to 23.04 Ma — Paleocene, Eocene and Oligocene; mammals radiate after the K–Pg extinction
- Neogene Period
- 23.04 to 2.58 Ma — the Miocene and Pliocene epochs; 'new born', named for fossils close to modern forms
- Quaternary Period
- 2.58 Ma to now — Pleistocene and Holocene; repeated ice ages. Base lowered from 1.8 Ma, ratified 2009
- The seven Cenozoic epochs, oldest first
- Paleocene, Eocene, Oligocene, Miocene, Pliocene, Pleistocene, Holocene
- Holocene Epoch
- 11,700 years ago to now — subdivided by the 2018 ratification into Greenlandian, Northgrippian, Meghalayan
Questions
- How do I print them double-sided?
- Double-sided, flip on the long edge. Every front sheet is followed by its own already-mirrored back sheet, so print them in the order they come and every answer lands on its own card.
- Can I edit the cards?
- Yes, and that is half the point. Once you own the deck, the "Buy & edit" button here opens all 29 cards in the free flash card maker on this site — reword a definition, delete the ones you do not teach, add your own, and print at anything from two to nine cards a page, rather than the fixed eight of the PDF.
- Can I print a set for every student?
- Yes. Personal and classroom licence: unlimited printing, every class you teach, every year you teach it. It does not cover reselling the file or passing it on to a colleague.
- What if I find a card that is wrong?
- Tell us and we fix it, and we publish what changed. We have withdrawn a whole deck from sale for being out of date rather than quietly patch it.
- Do I need an account?
- No. The file downloads straight away — no account, no email, no card details.