The Geologic Time Scale Flashcards

The Geologic Time Scale flashcards — the free 29

Every question and answer on the free cards, written out. 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

The Geologic Time Scale flashcards — questions people ask

How many cards are in the The Geologic Time Scale flashcard deck?

The The Geologic Time Scale deck on PuzzlePage has 29 cards, and all 29 are free to play and free to download with no account and no payment. 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.

What is on the the geologic time scale flashcards?

Every eon, era and Phanerozoic period with its span and what defines it, plus GSSPs and why the Tertiary and the Anthropocene are not on the ICS chart. Cards look like this: 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. The deck is written for grades 8–12 and filed under science.

Can I study the geologic time scale flashcards online for free?

Yes. All 29 cards of the The Geologic Time Scale deck play free in any web browser at puzzlepage.app, with no account, no app and no card details. It works on a phone, tablet, Chromebook, laptop or classroom projector. Practice mode flips through the cards with nothing scored; quiz mode makes you answer each card before it flips, times the run and scores it.

Are the the geologic time scale flashcards accurate?

Every card in the The Geologic Time Scale deck cites two independent published sources — two different organisations, not a standards body and a site reprinting it — and a script checks that, rather than taking the writer's word for it. A second specialist then re-verified the deck against sources of their own, without reading the citations first. That is the difference from a user-generated flashcard site, where the cards are whatever a stranger typed and nobody is accountable for them.

Can I print the the geologic time scale flashcards?

Yes. The The Geologic Time Scale cards are available as a printable double-sided PDF to cut up, as well as playable in the browser. The whole 29-card printable is free to download, with no account.

How should I use the The Geologic Time Scale deck to revise?

Start in practice mode and go through the The Geologic Time Scale deck once without scoring, to find out which cards you already know — the deck is dealt in a different order every time you open it, so you are recalling the card rather than its position. Then switch to quiz mode, which times and scores the run and lets you re-run only the cards you missed. Use the "flip deck" control to swap which side is the question: recognising an answer is much easier than producing one, so a deck you find easy one way round is usually the harder and more useful drill the other way. Two or three short sessions across a week beat one long one, which is the whole reason flashcards work.

What grade level are the the geologic time scale flashcards for?

The The Geologic Time Scale deck is written for grades 8–12. Because the cards are plain term-and-answer pairs, they are also used outside that band — by adults revising science, and by teachers running them as a whole-class starter on a projector.