Ages of the Earth

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Earth and human timelines.
Author

Stephen J. Mildenhall

Published

2024-02-26

Ages (divisions) of earth history and other historical milestones, provided by GPT/Gemini. Background for VSI reading, Guns, Germs, and Steel, etc.

Division hierarchy

In geology, the Earth’s history is organized into a hierarchical framework of time scales that help scientists communicate about the Earth’s past in a structured way. There are five: EEPEA:

  • Eon: \(10^8\) - \(10^9\) years ago
  • Era: \(10^7\) - \(10^8\)
  • Period: \(10^6\) - \(10^7\)
  • Epoch: \(10^5\) - \(10^6\)
  • Age: \(10^3\) - \(10^6\)

Here’s how each of these time scales is defined and distinguished:

Eon

  • Definition: The largest division of geologic time, encompassing billions of years.
  • Distinguishing Features: Eons mark fundamental shifts in Earth’s major geological systems and the evolution of life. There are four eons in the Earth’s history:
    • Hadean (Hell),
    • Archean (beginning or origin),
    • Proterozoic (former or earlier life), and
    • Phanerozoic (visible and abundant life.
    The Phanerozoic Eon, which is the current eon, covers the span of time from the explosion of life forms about 541 million years ago to the present.
    • Paleozoic Era (541 to 252 million years ago): Known for the Cambrian Explosion and the dominance of marine life, amphibians, and early reptiles.
    • Mesozoic Era (252 to 66 million years ago): The age of reptiles, including dinosaurs, and the spread of gymnosperms and later angiosperms (flowering plants).
    • Cenozoic Era (66 million years ago to the present): Characterized by the rise of mammals, the development of modern flora, and significant climatic shifts, leading to the current Quaternary Ice Age.

Era

  • Definition: Eras are subdivisions of eons and are significant periods of time marked by distinct and notable geological and paleontological1 events, such as mass extinctions or the dominance of particular life forms.
  • Distinguishing Features: For example, the Phanerozoic (latest) Eon is divided into three eras marked by major shifts in dominant lifeforms:
    • Paleozoic (ancient life),
    • Mesozoic (middle life), and
    • Cenozoic (recent life).
    Each era is characterized by significant shifts in the diversity and distribution of life on Earth.

Period

  • Definition: Periods are subdivisions of eras and are based on types of rock layers (stratigraphy) and significant events in Earth’s history, such as the development of major mountain ranges or the evolution of new species.
  • Distinguishing Features: Periods signify more specific changes in lifeforms and geological conditions than eras and can be identified by distinct rock formations and fossil records. For instance, the Mesozoic Era is divided into the Triassic, Jurassic, and Cretaceous periods, each marked by different life forms and geological events.

Epoch

  • Definition: Epochs are subdivisions of periods and are defined by smaller geological, paleontological or paleoclimatic events, such as minor extinctions, climate changes, or the appearance of specific types of flora and fauna.
  • Distinguishing Features: Epochs offer a more detailed resolution of geological time. For example, the Cenozoic Era’s Neogene Period is divided into the Miocene and Pliocene epochs, among others, each characterized by specific climatic conditions and life forms.

Age

  • Definition: Ages are the smallest units of geological time and are often defined by the presence of certain types of fossils or by minor geological events.
  • Distinguishing Features: Ages provide the finest resolution of geological time marked by very specific intervals marked by very particular assemblages of fossils. They can often be correlated with specific layers of rock (strata). For example, within the Cretaceous Period, the Late Cretaceous is further divided into ages such as the Campanian and Maastrichtian, each identified by particular fossil assemblages and stratigraphic markers.

This hierarchical structure allows geologists to discuss Earth’s history with precision, identifying events and conditions that occurred at specific times throughout the planet’s 4.6 billion-year history.

How are they distinguished?

In practice, these distinctions are based on a combination of factors:

  • Radiometric Dating: Provides absolute dates in millions of years.
  • Stratigraphy: The study of rock layers and their correlation.
  • Paleontology: The study of fossilized organisms, major evolutionary events, and extinction events.

Divisions of Earth’s History

In million years ago, Mya.

History of the earth showing geologic clock with events and periods, source: Wikipedia

History of the earth showing geologic clock with events and periods, source: Wikipedia
Abbreviated Table, Holocene started 11,700 years ago, after the last major ice age.
Years Ago (Mya) Eon Era Period Epoch
4600 - 4000 Hadean
4000 - 2500 Archean
4031 - 3600 Eoarchean
3600 - 3200 Paleoarchean
3200 - 2800 Mesoarchean
2800 - 2500 Neoarchean
2500 - 540 Proterozoic
2500 - 1600 Paleoproterozoic
2500 - 2300 Siderian
2300 - 2050 Rhyacian
2050 - 1800 Orosirian
1800 - 1600 Statherian
1600 - 1000 Mesoproterozoic
1600 - 1400 Calymmian
1400 - 1200 Ectasian
1200 - 1000 Stenian
1000 - 540 Neoproterozoic
1000 - 720 Tonian
720 - 635 Cryogenian
635 - 540 Ediacaran
540 - now Phanerozoic
540 - 485 Paleozoic Cambrian
485 - 444 Ordovician
444 - 419 Silurian
419 - 359 Devonian
359 - 299 Carboniferous
299 - 252 Permian
252 - 201 Mesozoic Triassic
201 - 145 Jurassic
145 - 66 Cretaceous Campanian
Maastrichtian
66 - now Cenozoic
66 - 23 Paleogene Paleocene
56 - 33.9 Eocene
33.9 - 23 Oligocene
23 - 2.58 Neogene Miocene
5.33 - 2.58 Pliocene
2.58 - 0.0117 Quaternary Pleistocene
0.0117 - 0 Holocene
now Anthropocene
More detailed table.
Years Ago (Mya) Eon / Era / Period / Epoch Notable Characteristics
4600 - 4000 Hadean Formation of Earth, very high temperatures, no life.
4000 - 2500 Archean Formation of the first continental crust, appearance of the earliest known life forms.
4031 - 3600 ./ Eoarchean Formation of the Earth’s crust, earliest known life forms
3600 - 3200 ./ Paleoarchean Continued crust formation, emergence of early life
3200 - 2800 ./ Mesoarchean Stabilization of continental crusts, archaean life
2800 - 2500 ./ Neoarchean Increase in crustal growth, evidence of early life forms
2500 - 540 Proterozoic
2500 - 1600 ./ Paleoproterozoic Great Oxygenation Event, significant increase in atmospheric oxygen.
2500 - 2300 ../ Siderian
2300 - 2050 ../ Rhyacian
2050 - 1800 ../ Orosirian
1800 - 1600 ../ Statherian
1600 - 1000 ./ Mesoproterozoic Stabilization of Earth’s atmosphere, emergence of eukaryotic cells.
1600 - 1400 ../ Calymmian
1400 - 1200 ../ Ectasian
1200 - 1000 ../ Stenian
1000 - 540 ./ Neoproterozoic Ediacaran biota, increase in multicellular life.
1000 - 720 ../ Tonian
720 - 635 ../ Cryogenian
635 - 540 ../ Ediacaran
540 - now Phanerozoic
540 - 253 ./ Paleozoic
540 - 485 ../ Cambrian “Cambrian Explosion” of marine life, development of diverse life forms.
485 - 444 ../ Ordovician Marine life diversification, first land plants, ends with large extinction event.
444 - 419 ../ Silurian First vascular plants and terrestrial ecosystems, marine life diversification.
419 - 359 ../ Devonian “Age of Fishes”, first amphibians, significant plant evolution.
359 - 299 ../ Carboniferous Large coal-forming forests, evolution of reptiles, large insect forms.
299 - 252 ../ Permian Pangea supercontinent formation, ends with the largest extinction event.
252 - 66 ./ Mesozoic
252 - 201 ../ Triassic Recovery from Permian extinction, first dinosaurs and mammals.
201 - 145 ../ Jurassic Age of Reptiles, significant dinosaur diversification.
145 - 66 ../ Cretaceous Flowering plants appear, large dinosaurs, ends with mass extinction.
145 - 66 …/ Campanian
…/ Maastrichtian
66 - now ./ Cenozoic
66 - 23 ../ Paleogene Mammals rise to dominance, major avian diversification.
66 - 23 …/ Paleocene
56 - 33.9 …/ Eocene
33.9 - 23 …/ Oligocene
23 - 2.58 ../ Neogene Hominids appear, cooling climate, grasslands expand.
23 - 2.58 …/ Miocene
5.33 - 2.58 …/ Pliocene
2.58 - 0.0117 ../ Quaternary
2.58 - 0.0117 …/ Pleistocene Ice ages, human evolution.
0.0117 - 0 …/ Holocene Modern climate period, rise of human civilizations. Most recent ice age.
now …/ Anthropocene

Relevant articles

In the earlier eons—Hadean, Archean, and Proterozoic—the concept of “eras” is less frequently applied in the same detailed manner as it is within the Phanerozoic eon. This is primarily because the geological and fossil records from these eons are less detailed and less abundant than those from the Phanerozoic, making it more challenging to define distinct “eras” based on life forms or significant geological events. However, for more detailed scientific study and classification, these earlier eons are subdivided into various units, including eras, periods, and even epochs in some cases, though these divisions are based more on geological and chemical changes than on the diversity of life, which is the more common basis for divisions in the Phanerozoic.

Glossary

Here’s a glossary of terms often encountered in geology and paleontology, with explanations and etymological clues to help decipher their meanings:

  • Hadean Eon: Derived from Hades, indicating the very ancient, hellish conditions of Earth’s surface shortly after its formation. It’s the earliest eon in Earth’s history, before the appearance of the first known rocks.

  • Archean Eon: From the Greek “archaios,” meaning ancient or original. This eon follows the Hadean and is characterized by the formation of the Earth’s first continental crust and the earliest known life forms.

  • Proterozoic Eon: From Greek “proteros,” meaning former, earlier, and “zoic,” referring to life. This eon is marked by the appearance of oxygen in the atmosphere and the first complex life forms.

  • Phanerozoic Eon: From Greek “phaneros,” visible, and “zoic,” life. This is the current eon, characterized by abundant and diverse life forms, with a rich fossil record.

  • Paleozoic Era: “Paleo-” means old, and “zoic” refers to life. The era of “old life,” marked by the emergence and evolution of life in the seas, land plants, and the first terrestrial animals.

  • Mesozoic Era: “Meso-” means middle. Known as the era of “middle life,” it’s famous for the dominance of dinosaurs and the appearance of the first mammals and birds.

  • Cenozoic Era: “Ceno-” means new. This era of “new life” follows the extinction of the dinosaurs and is characterized by the rise of mammals and birds.

  • Cambrian Period: Named after Cambria, the Roman name for Wales, where rocks from this time were first studied. Marks the beginning of the Paleozoic era, notable for the “Cambrian Explosion” of life.

  • Ordovician, Silurian, Devonian, Carboniferous, and Permian Periods: These periods are named after regions (e.g., the Devonian after Devon, England) or characteristics of the rock strata or life forms found within those periods.

  • Triassic, Jurassic, and Cretaceous Periods: The Mesozoic era’s periods, named after the three distinct rock layers (tri-, “three”; Jura, a mountain range in Europe; and “Creta,” meaning chalk) that define them.

  • Paleogene and Neogene Periods: Components of the Cenozoic era. “Paleogene” (old born) and “Neogene” (new born) indicate the relative ages of life forms found within these periods.

  • Quaternary Period: From “quartus,” meaning fourth, initially considered the fourth period of the Cenozoic era. It includes the current geological time, marked by significant ice ages.

  • Pleistocene Epoch: From “pleistos,” most, and “kainos,” new, referring to the most recent ice ages.

  • Holocene Epoch: From “holos,” whole, and “kainos,” new, indicating the entirely recent epoch, which follows the last ice age and includes modern human civilization.

  • Cenozoic: Means “new life,” indicating the era of modern life forms.

  • Mesozoic: Means “middle life,” reflecting its position between the Paleozoic and Cenozoic.

  • Paleozoic: Means “ancient life,” highlighting the era’s old, primitive life forms.

Etymological Clues

Common Prefixes

  • Ceno-: means new, used for more recent geological time periods.
  • Eo-: means “dawn”
  • Oligo-: means “few”
  • Paleo-: means old, indicating ancient times or organisms. (ex: Paleozoic – “ancient life”).
  • Meso-: means middle, used for time periods between ancient and modern. (ex: Mesozoic – “middle life”).
  • Neo- (from Greek ‘neos’): means “new” or “recent”.
  • Pre-: means “before” (ex: Precambrian – the time before the Cambrian period).
  • Protero- (from Greek ‘proteros’): means “earlier” or “former”.

Common Suffixes

  • -an, -ian: Used to form adjectives, signifies “of or relating to” (ex: Devonian – period relating to Devonshire, England, where rocks of this age were first studied).
  • -cene (from Greek ‘kainos’): meaning “new” or “recent.” Used to denote epochs within larger eras (ex: Pleistocene – “most recent”).
  • -ic: means “relating to.”
  • -lith, -lite (from Greek ‘lithos’): meaning “stone” or “rock.” Often used in names referring to specific types of rock formations.
  • -ous: means “having the quality of.”
  • -zoic: refers to life, used in the names of eons and eras to denote time periods characterized by certain forms of life. Periods with this root are broadly defined by the types of life present (ex: Cenozoic – “recent life”).

Mass Extinction Events

Below is a markdown table summarizing the “Big Five” mass extinctions in Earth’s history, including their names, approximate dates, causes, and impact in terms of the percentage of species that went extinct:

GPT table
Name Mya Cause Impact (Percentage of Species Extinct)
Ordovician-Silurian 444 Climate change, sea level fall, and possibly gamma-ray burst 85%
Late Devonian 372 Global cooling, volcanic activity, and asteroid impacts 75%
Permian-Triassic 252 Volcanic activity, methane release, and anoxia (lack of oxygen) 96%
Triassic-Jurassic 201 Volcanic activity leading to climate change, ocean acidification 80%
Cretaceous-Paleogene 66 Asteroid impact, volcanic activity, climate change 76%

These extinctions had profound impacts on Earth’s biodiversity, each with its own set of causes ranging from volcanic activity and asteroid impacts to dramatic changes in climate and sea levels. The Permian-Triassic extinction event, also known as the “Great Dying,” was the most severe, with an estimated 96% of all species going extinct.

Early Human Migrations

Peopling of the world (recent out of Africa and Upper Paleolithic). Figures are in thousands of years ago (kya). Time is color coded in a scheme of increasing “frequency”, red at 100 kya to violet at 0 kya. Dotted blueish lines are meant to indicate approximate glaciation during the Last Glacial Maximum (LGM).

Overview map of the peopling of the world by early humans during the Upper Paleolithic, following the Southern Dispersal paradigm.

Overview map of the peopling of the world by early humans during the Upper Paleolithic, following the Southern Dispersal paradigm.

By User:Dbachmann - Own work;Map: File:World map blank shorelines.svg (the shoreline map is {{PD-USGov-USGS}}, derived from a mercator svg map posted in 2005, extracted from an original file released by pubs.usgs.gov), CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=68921860

Human History

Timeline of human evolution

A tabular overview of the taxonomic ranking of Homo sapiens (with age estimates for each rank) is shown below.

Rank Name Common name Millions of years ago (commencement)
Life 4,200
Archaea 3,700
Domain Eukaryota Eukaryotes 2,100
Podiata Excludes Plants and their relatives 1,540
Amorphea
Obazoa Excludes Amoebozoa (Amoebas)
Opisthokonts Holozoa + Holomycota (Cristidicoidea and Fungi) 1,300
Holozoa Excludes Holomycota 1,100
Filozoa Choanozoa + Filasterea
Choanozoa Choanoflagellates + Animals 900
Kingdom Animalia Animals 610
Subkingdom Eumetazoa Excludes Porifera (Sponges)
Parahoxozoa Excludes Ctenophora (Comb Jellies)
Bilateria Triploblasts / Worms 560
Nephrozoa
Deuterostomes Division from Protostomes
Phylum Chordata Chordates (Vertebrates and closely related invertebrates) 530
Olfactores Excludes cephalochordates (Lancelets)
Subphylum Vertebrata Fish / Vertebrates 505
Infraphylum Gnathostomata Jawed fish 460
Teleostomi Bony fish 420
Sarcopterygii Lobe finned fish
Superclass Tetrapoda Tetrapods (animals with four limbs) 395
Amniota Amniotes (fully terrestrial tetrapods whose eggs are “equipped with an amnion”) 340
Synapsida Proto-Mammals 308
Therapsid Limbs beneath the body and other mammalian traits 280
Class Mammalia Mammals 220
Subclass Theria Mammals that give birth to live young (i.e., non-egg-laying) 160
Infraclass Eutheria Placental mammals (i.e., non-marsupials) 125
Magnorder Boreoeutheria Supraprimates, (most) hoofed mammals, (most) carnivorous mammals, cetaceans, and bats 124–101
Superorder Euarchontoglires Supraprimates: primates, colugos, tree shrews, rodents, and rabbits 100
Grandorder Euarchonta Primates, colugos, and tree shrews 99–80
Mirorder Primatomorpha Primates and colugos 79.6
Order Primates Primates / Plesiadapiformes 66
Suborder Haplorrhini “Dry-nosed” (literally, “simple-nosed”) primates: tarsiers and monkeys (incl. apes) 63
Infraorder Simiiformes monkeys (incl. apes) 40
Parvorder Catarrhini “Downward-nosed” primates: apes and old-world monkeys 30
Superfamily Hominoidea Apes: great apes and lesser apes (gibbons) 22-20
Family Hominidae Great apes: humans, chimpanzees, gorillas and orangutans—the hominids 20–15
Subfamily Homininae Humans, chimpanzees, and gorillas (the African apes)[1] 14–12
Tribe Hominini Includes both Homo, Pan (chimpanzees), but not Gorilla. 10–8
Subtribe Hominina Genus Homo and close human relatives and ancestors after splitting from Pan—the hominins 8–4[2]
(Genus) Ardipithecus s.l. 6-4
(Genus) Australopithecus 3
Genus Homo (H. habilis) Humans 2.5
(Species) H. erectus s.l.
(Species) H. heidelbergensis s.l.
Species Homo sapiens s.s. Anatomically modern humans 0.8–0.3[3]

Footnotes

  1. Paleontology is the scientific study of life that existed in the past, primarily through the examination of fossils.↩︎