Geologic Time Scale

Oct 12, 2022 | reading

I'm currently reading Thomas Halliday's Otherlands about the history of life on earth. There is a little table of eons, eras, periods and epochs at the beginning of the book, but it only contains names and dates. To get some more orientation, I went over to Wikipedia's Geological time scale article and fell down a bit of a rabbit hole, following links and collecting bits of information. The result is the following table with copy-pasted facts that seemed familiar or interesting to me, sorted into epochs and periods. All times are given in millions of years. Disclaimer: the selection of included facts is arbitrary and probably there are some inaccuracies.

Reasonably wide display strongly recommended!

Eon	Era	Period	Epoch	Start	Description
Phanerozoic	Cenozoic	Quaternary	Holocene	0.0117	Glacial retreat. Rapid rise of human species.
Pleistocene	2.58	Ice Age, repeated glaciations resulting in lower sea levels (> 100m) → Bering land bridge (Beringian refugium). † Homo erectus, Homo sapience (0.3).
Neogene	Pliocene	5.333	Appearance of Homo (2.6), genus including modern humans. Formation of Isthmus of Panama, linking North and South America → Great American Interchange → end of some indigenous South American animals. Strait of Gibraltar opened (5.333) and Mediterranean refilled (Zanclean flood). Beringia first flooded.
Miocene	23.03	Collision of Arabian Peninsula with Eurasia cut off Mediterranean from Indian Ocean and connection between Atlantic and Mediterranean closed → Mediterranean nearly dried up (Messinian salinity crisis).
Palaeogene	Oligocene	33.9	Replacement of European fauna with Asian fauna (Grande Coupure). Global expansion of grasslands, regression of tropical broad leaf forests to equatorial belt.
Eocene	56	Concentration of ¹³C in atmosphere exceptionally low at start. Forests cover most of the Earth, including poles (palm trees in Alaska and northern Europe). First fossils of most modern mammals.
Paleocene	66	Starts with Chicxulub impact and K-Pg extinction (66): † 75% of all species, among them all non-avian dinosaurs.
Mesozoic	Cretaceous		145	Breakup of Gondwana accelerates: South America, Antarctica and Australia rifted away from Africa, South Atlantic and Indian Oceans newly formed. Warm climate, high sea levels. Large areas of continents covered by warm, shallow seas → marine limestone deposits from calcite skeletons of algae (chalk, white cliffs of Dover, Rügen). Stagnation of deep sea currents → anoxic conditions → deposited organic matter undecomposed (half of world's petroleum reserves in today's Persian Gulf and Gulf of Mexico). Formation of dark anoxic shales → source rock for oil and gas. First fossils of grasses. Most diverse stage of dinosaurs.
Jurassic	201.3	Gondwana breakup begins. Toarcian Oceanic Anoxic Event (TOAE, aka Jenkyns Event): widespread oceanic anoxia → deposition of black shales → largest oil reserves (North Sea, Saudi Arabia, Iraq); Sichuan Basin transformed into giant lake → sequestered large amounts of carbon. Ginkgoales more diverse than today, widespread in Eurasia. Dinosaurs become dominant vertebrates in terrestrial ecosystems after end-Triassic extinction. First birds evolve from dinosaurs; first lizards, sharks, rays, crabs.
Triassic	251.9	Interior: Hot and dry continental climate. Polar regions: moist and temperate, suitable for forests and vertebrates. * First archosaurs (ancestors of birds and crocodilians), dinosaurs (subgroup of archosaurs), modern corals, modern amphibians. Triassic-Jurassic extinction (201.3): † 70-75% of all species. Pangaea begins breaking up into Gondwana and Laurasia (200).
Paleozoic	Permian	298.9	Vast deserts within Pangea after Carboniferous rainforest collapse. 3-4 extinction events, last: Permian-Triassic extinction (252): † 90-96% of all species (largest in Earth's history).
Carboniferous	358.9	coal-bearing: many coal beds formed globally from vast forests. Age of amphibians: amphibians dominant land vertebrates, diversified into many forms (lizard-like, snake-like, crocodile-like). Later glaciations, low sea level, mountain building as continents collided to form Pangaea. Minor extinction event: Carboniferous rainforest collapse.
Devonian	419.2	First significant adaptive radiation of life on dry land. Extensive forests, leaves and roots evolved, first seed-bearing pants. Age of fishes: substantial diversity. First ammonites. Late Devonion extinction (375-360): † 70% of all species.
Silurian	443.8	First megafossils (visible without microscope) of extensive terrestrial biota: moss-like miniature forests. First fossil records of vascular plants (land plants with tissues carrying water and food). First bony fish, development of movable jaws in fish. First animals fully adapted to terrestrial conditions.
Ordovician	485.4	Ordovician radiation: great biodiversification. Molluscs and arthropods dominate oceans; the latter start their establishment on land. First land plants. Ordovician-Silurian extinction events (450-440): † 85% of all species.
Cambrian	541	Cambrian explosion: rapid diversification of lifeforms, first representatives of all modern animal phyla, spread of animals with mineral skeletons and shells → better fossil record. First vertebrates.
Proterozoic	Neoproterozoic	Ediacaran	635	Avalon explosion (575): * widespread multicellular fauna after Snowball Earth glaciation events, most of which † during End-Ediacaran extinction event (539). Last stage of formation of supercontinent Gondwana.
Cryogenian	720	Earth's surface possibly (almost) entirely frozen (Snowball Earth hypothesis). First uncontroversial animal fossils (rare).
Tonian	1000	Breakup of Rodinia (900-850). First hypothetical animals.
Mesoproterozoic	Stenian	1200	Supercontinent Rodinia assembled. * Fossils of oldest sexually reproducing organism (type of red algae, sometimes dated to Ectasian).
Ectasian	1400	Continued expansion of platform covers. More complex microfossils, also found on land, fungus-like organisms and microbes.
Calymmian	1600	Supercontinent Columbia starts to break (1500). Expansion of existing platform covers (sedimentary strata, which overlie basement of rocks of earlier deformation), new platforms.
Paleoproterozoic	Statherian	1800	Supercontinent Columbia has assembled. New platforms or final cratonization of fold belts. Oxygen levels 10% to 20% of current values. First fossil records of eukaryotes
Orosirian	2050	Intense orogeny (formation of mountains by collision of tectonic plates) on all continents: Asteroid collisions: Vredefort impact structure (2023), Sudbury Basin structure (1850).
Rhyacian	2300	Huronian global glaciation begins. First record of multicellular life (Francevillian biota, aka Gabon macrofossils, 2100). Probably first eukaryotes (organism with cells that have nucleus enclosed in nuclear envelope).
Siderian	2500	Deposition of banded iron formations peaked when iron rich formations formed as cyanobacteria produced waste oxygen → iron oxide. Removed iron from Earth's oceans, turning greenish seas clear. Without iron, oceans no longer oxygen sink, allowing buildup of oxygen-rich atmosphere, which triggered oxygen catastrophe: oxygen in atmosphere → † anaerobic species on Earth. May have triggered Huronian glaciation.

Eon

Era

Period

Epoch

Start

Description

Phanerozoic

Cenozoic

Quaternary

Holocene

0.0117

Glacial retreat. Rapid rise of human species.

Pleistocene

2.58

Ice Age, repeated glaciations resulting in lower sea levels (> 100m) → Bering land bridge (Beringian refugium). *† Homo erectus, * Homo sapience (0.3).

Neogene

Pliocene

5.333

Appearance of Homo (2.6), genus including modern humans. Formation of Isthmus of Panama, linking North and South America → Great American Interchange → end of some indigenous South American animals. Strait of Gibraltar opened (5.333) and Mediterranean refilled (Zanclean flood). Beringia first flooded.

Miocene

23.03

Collision of Arabian Peninsula with Eurasia cut off Mediterranean from Indian Ocean and connection between Atlantic and Mediterranean closed → Mediterranean nearly dried up (Messinian salinity crisis).

Palaeogene

Oligocene

33.9

Replacement of European fauna with Asian fauna (Grande Coupure). Global expansion of grasslands, regression of tropical broad leaf forests to equatorial belt.

Eocene

Concentration of ¹³C in atmosphere exceptionally low at start. Forests cover most of the Earth, including poles (palm trees in Alaska and northern Europe). First fossils of most modern mammals.

Paleocene

Starts with Chicxulub impact and K-Pg extinction (66): † 75% of all species, among them all non-avian dinosaurs.

Mesozoic

Cretaceous

145

Breakup of Gondwana accelerates: South America, Antarctica and Australia rifted away from Africa, South Atlantic and Indian Oceans newly formed. Warm climate, high sea levels. Large areas of continents covered by warm, shallow seas → marine limestone deposits from calcite skeletons of algae (chalk, white cliffs of Dover, Rügen). Stagnation of deep sea currents → anoxic conditions → deposited organic matter undecomposed (half of world's petroleum reserves in today's Persian Gulf and Gulf of Mexico). Formation of dark anoxic shales → source rock for oil and gas. First fossils of grasses. Most diverse stage of dinosaurs.

Jurassic

201.3

Gondwana breakup begins. Toarcian Oceanic Anoxic Event (TOAE, aka Jenkyns Event): widespread oceanic anoxia → deposition of black shales → largest oil reserves (North Sea, Saudi Arabia, Iraq); Sichuan Basin transformed into giant lake → sequestered large amounts of carbon. Ginkgoales more diverse than today, widespread in Eurasia. Dinosaurs become dominant vertebrates in terrestrial ecosystems after end-Triassic extinction. First birds evolve from dinosaurs; first lizards, sharks, rays, crabs.

Triassic

251.9

Interior: Hot and dry continental climate. Polar regions: moist and temperate, suitable for forests and vertebrates. * First archosaurs (ancestors of birds and crocodilians), dinosaurs (subgroup of archosaurs), modern corals, modern amphibians. Triassic-Jurassic extinction (201.3): † 70-75% of all species. Pangaea begins breaking up into Gondwana and Laurasia (200).

Paleozoic

Permian

298.9

Vast deserts within Pangea after Carboniferous rainforest collapse. 3-4 extinction events, last: Permian-Triassic extinction (252): † 90-96% of all species (largest in Earth's history).

Carboniferous

358.9

coal-bearing: many coal beds formed globally from vast forests. Age of amphibians: amphibians dominant land vertebrates, diversified into many forms (lizard-like, snake-like, crocodile-like). Later glaciations, low sea level, mountain building as continents collided to form Pangaea. Minor extinction event: Carboniferous rainforest collapse.

Devonian

419.2

First significant adaptive radiation of life on dry land. Extensive forests, leaves and roots evolved, first seed-bearing pants. Age of fishes: substantial diversity. First ammonites. Late Devonion extinction (375-360): † 70% of all species.

Silurian

443.8

First megafossils (visible without microscope) of extensive terrestrial biota: moss-like miniature forests. First fossil records of vascular plants (land plants with tissues carrying water and food). First bony fish, development of movable jaws in fish. First animals fully adapted to terrestrial conditions.

Ordovician

485.4

Ordovician radiation: great biodiversification. Molluscs and arthropods dominate oceans; the latter start their establishment on land. First land plants. Ordovician-Silurian extinction events (450-440): † 85% of all species.

Cambrian

541

Cambrian explosion: rapid diversification of lifeforms, first representatives of all modern animal phyla, spread of animals with mineral skeletons and shells → better fossil record. First vertebrates.

Proterozoic

Neoproterozoic

Ediacaran

635

Avalon explosion (575): * widespread multicellular fauna after Snowball Earth glaciation events, most of which † during End-Ediacaran extinction event (539). Last stage of formation of supercontinent Gondwana.

Cryogenian

720

Earth's surface possibly (almost) entirely frozen (Snowball Earth hypothesis). First uncontroversial animal fossils (rare).

Tonian

1000

Breakup of Rodinia (900-850). First hypothetical animals.

Mesoproterozoic

Stenian

1200

Supercontinent Rodinia assembled. * Fossils of oldest sexually reproducing organism (type of red algae, sometimes dated to Ectasian).

Ectasian

1400

Continued expansion of platform covers. More complex microfossils, also found on land, fungus-like organisms and microbes.

Calymmian

1600

Supercontinent Columbia starts to break (1500). Expansion of existing platform covers (sedimentary strata, which overlie basement of rocks of earlier deformation), new platforms.

Paleoproterozoic

Statherian

1800

Supercontinent Columbia has assembled. New platforms or final cratonization of fold belts. Oxygen levels 10% to 20% of current values. First fossil records of eukaryotes

Orosirian

2050

Intense orogeny (formation of mountains by collision of tectonic plates) on all continents: Asteroid collisions: Vredefort impact structure (2023), Sudbury Basin structure (1850).

Rhyacian

2300

Huronian global glaciation begins. First record of multicellular life (Francevillian biota, aka Gabon macrofossils, 2100). Probably first eukaryotes (organism with cells that have nucleus enclosed in nuclear envelope).

Siderian

2500

Deposition of banded iron formations peaked when iron rich formations formed as cyanobacteria produced waste oxygen → iron oxide. Removed iron from Earth's oceans, turning greenish seas clear. Without iron, oceans no longer oxygen sink, allowing buildup of oxygen-rich atmosphere, which triggered oxygen catastrophe: oxygen in atmosphere → † anaerobic species on Earth. May have triggered Huronian glaciation.