Geologic time scale

• Geologic Time Scale

  The stratigraphic history of the Earth
• Stratigraphy


  The ordering and analysis of the Earth's layers (known as a bed or strata) based on chronological dating techniques and relative positions with each other
• The Earth is at least 4.6 billion years old, almost sharing its age with the Sun
• Humans have thrived for less than a percent of the Earth's existence
• Eon


  The largest time division, lasting billions of years
• Era


  A subdivision of an eon, scaling hundreds of millions of years
• Period


  A subdivision of an era, lasting tens of millions of years
• Epoch


  A subdivision of a period, lasting around several million years
• Precambrian Supereon


  The early period of the Earth's history, containing three eons
• Hadean Eon


  The earliest iteration of the Earth, devoid of life and still made of molten material
• Highlights of the Hadean Eon


  • Formation of the moon
  • Formation of the Earth
  • The Iron Catastrophe
  • The Earth's magnetic field began to manifest
  • The first solid continental crust is formed
  • Several Bombardment events occurred
  • Continents began to form from continental crusts
• Archaean Eon


  The period after the Hadean Eon when the newly formed crust began to cool down, forming shield rocks
• Highlights of the Archaean Eon


  • The first rain fell on Earth
  • Microfossils indicate chemoautotrophs were the first living organisms
  • The formation of the first atmosphere
  • The birth of extremophiles
  • The dissolution and utility of carbon
  • The formation of the first supercontinent, Vaalbara
• Craton


  A large stable block of crust, which forms a continent's base for expansion and growth
• Proterozoic Eon


  The period where life began to dominate the Earth's surface
• Supercontinents formed in the Proterozoic Eon


  • Arctica
  • Atlantica and Columbia (Nuna)
  • Rodinia
  • Pannotia
• Highlights of the Proterozoic Eon


  • The birth of photosynthetic organisms and "energy-converting" organisms
  • The First Ice Age
  • The First Extinction of carbon-dependent prokaryotes
• Phanerozoic Eon


  The eon where eukaryotes began to dominate the scene
• Paleozoic Era


  The period where eukaryotes began to dominate the scene, also known as the Age of Invertebrates
• Periods and Highlights of the Paleozoic Era


  • Cambrian Period: Cambrian Explosion, ichnofossils, first fish and early vertebrates, armored arthropods
  • Ordovician Period: Speciation of evolved organisms, armored and shelled organisms, second Ice Age
  • Silurian Period: Healing after Ice Age, evolution of fish, arthropods as dominant predators, first vascular plants
  • Devonian Period: Age of the Fish, first amphibians, plant diversification, Late Devonian extinction
  • Carboniferous Period: Varied rock deposits, high global temperatures, tropical swamps, growth of lignin-laden plants and trees
• Pannotia eventually broke up and reformed as Gondwana, which is unique because its landmasses were divided
• Devonian Period


  Age of the Fish due to the enormous diversification and speciation of fish
• Devonian Period


  • First amphibians evolved
  • Plants diversified on land, developing the first trees alongside the development of lignin and seeds
  • Arthropods gained new habitats but made the fish the new dominant predators
  • Some volcanic island arcs and sandstone were primarily built
  • At least 70% of all species became extinct due to the Late Devonian extinction, which is primarily caused by plant domination
• Carboniferous Period


  Rocks dated in this period are varied, including limestone, sandstone, shale, and coal, with coal deposits dominating
• Carboniferous Period


  • Average global temperatures were exceedingly high
  • Tropical swamps were developed
  • Lignin-laden plants and trees grew taller and became more numerous, including seed ferns
  • Amniotic eggs were developed, allowing amphibians to go farther inland and become the dominant vertebrate
  • The first reptiles appeared
  • Because of the cool global temperatures, rainforests collapsed and a third Ice Age came
• Permian Period


  • All separate continents formed Pangaea
  • The major marker is the Ural mountains
  • Reptiles dominated the scene, with early dinosaurs such as Dimetrodon and Edaphosaurus evolving and dominating Pangaea
  • The first cone-bearing plants (true conifers and cycads) and the ginkgo evolved and thrived
  • Near the end, Pangaea became drier, thus creating more deserts
  • More vertebrates dominated the scene, such as Scutosaurus and Gorgonopsids
  • Eventually, a third extinction came, which is known as The Great Dying
• Mesozoic Era


  The Land Before Time, the Age of Reptiles or Age of the Dinosaurs, where the Earth began to recover from its third extinction
• Triassic Period


  • Marked the boom in reptilian evolution after The Great Dying, where almost 95% of all known species during the Permian Period became extinct
  • Divided into three epochs: Early, Middle, and Late Triassic
  • Temnospondyls became the dominant lifeform
  • The first mammals appeared
  • Pangaea broke up and formed the Tethys Ocean
  • Ecosystems and marine life slowly recovered
  • Pine trees, mosquitoes, and fruit flies flourished
  • Because of the fluctuating climate, a fourth extinction occurred at the transition period to Jurassic
• Jurassic Period

  • Divided into three epochs: Early, Middle, and Late Jurassic
  • Rock samples are mostly limestone
  • Global climate became more tropical than Triassic
  • Plesiosaurs, ichthyosaurs, and ammonites dominated the oceans
  • Land lifeforms continued to compete for dominance, such as the Dilophosaurus, Diplodocus, Allosaurs, and Brachiosaurus
  • The first true crocodiles evolved, pushing large amphibians to near extinction
  • Mammals began to evolve as well, remaining relatively small but prolific
  • The first birds appeared, with the Archaeopteryx and the Aurornis as the well-known species
• Cretaceous Period

  • The longest period in the Mesozoic era, but only contains two epochs: Early and Late Cretaceous
  • Contains the most fossil samples of the Mesozoic era, creating limestone layers
  • Seaways began to expand, which led to the extinction of sauropods (herbivore dinosaurs)
  • Seasonal climates returned, but dinosaurs still roamed the polar forests
  • Mammals began to expand their ranges
  • Temperatures began to slowly lower until the Cenozoic era
  • New dinosaur such as the Tyrannosaurus, Ankylosaurus, and Triceratops began to boom
  • The fifth extinction of most non-avian dinosaurs may have been caused by an asteroid impact, where ¾ of the total species on Earth were wiped out
  • The first primates and flowering plants appeared
• Cenozoic Era

  The Age of Mammals, where mammals began to dominate the Earth
• Paleocene

  • The "old part of the Eocene"
  • Because of the asteroid impact during the late Cretaceous period, carbon content increases, resulting in acidification of oceans and a spike in global temperature
  • Pangaea was somehow still intact, but distinct regions began to form
  • With the death of the giant non-avian dinosaurs, mammals began to roam the Earth despite having ambiguous classifications
• Eocene

  • Carbon-13 in the atmosphere was at its all-time low compared to Carbon-12
  • Ended with the Grande Coupure, a significant extinction event where most European fauna were replaced by Asian fauna
  • Pangaea fragmented and began to move away from each other, with Australia and Antarctica still connected
  • Palm trees expanded its territory, but not as much on the northern areas
  • Ungulates, artiodactyls, perissodactyls, and primates began to roam the lands
• Oligocene

  • Only a few fossil specimens were recorded to be from this epoch, which were all obtained in Germany
  • Global temperatures began to decline slowly
  • Continents were still in motion, with Antarctica occupying the South pole completely, isolating it from the rest
  • Orogeny occurred in North America and Europe
  • Deciduous plants began to evolve in this period
  • Plains and deserts became more common
• Miocene

  • It contains 18% fewer sea invertebrate species
  • It marked the era of consecutive ice ages
  • Apes began to dominate the scene, with the human ancestors deviating from its chimpanzee species
  • Most modern species of plants and animals evolved from this period
  • Grasslands began to expand, while kelp forests first appeared here
• Pliocene

  • Global sea levels were 25 meter higher than it is today
  • Continents are still in motion, with South America linking with North America via the Isthmus of Panama
  • Africa collided with Europe, forming the Mediterranean Sea
  • Therein exists a land bridge between Alaska and Siberia
  • Deciduous forests began to proliferate, pushing conifers further up north
  • New biomes appeared, as well as the Australopithecus, the very first hominin (i.e., human-like organism)
• Pleistocene

  • The period humans are familiar with as the Ice Age, with multiple glaciations occurring during this time
  • Glaciers once transported non-marine sediments found in riverbeds, lakebeds, slope, and loess deposits worldwide
  • Mammals such as mammoths, mastodons, the Smilodon, giant sloths, and the Gigantopithecus once roamed the Earth
• Holocene

  The period after the last Ice Age, where human species began to boom, with the advancements of technology, livelihood, infrastructures, and knowledge, which includes the present time
• Anthropocene

  The proposed new epoch that describes man's advancement impacting the ecosystems worldwide, and covers the advancement of digital technology and the sudden increase in global temperatures due to human-made climate change
• Proterozoic Eon

  The First Freezer