earth's history

• What marks the beginning of Earth's history?

  The formation of the solar system
• What are the major units of the geologic time scale?

  • Eon
  • Era
  • Period
  • Epoch
• What are the two types of evidence used for the geologic time scale?

  • Rocks
  • Fossils
• What was Earth like millions of years ago?

  • Covered with a thick blanket of ice
  • Lots of volcanoes and high mountains
  • Large organisms roamed the land
  • Low oxygen content in the atmosphere
  • Frequent asteroid/meteor impacts
  • Continents were closer together
  • Volcanic eruptions occurred
  • A little bit warmer
  • Plants were larger
  • Humans were not yet around
• What is the age of the Earth?
• What fields do geologists study to reconstruct Earth's history?

  • Petrology
  • Stratigraphy
  • Paleontology
• What does petrology study?

  The origin, composition, structure, and classification of rocks
• What is stratigraphy concerned with?

  The study of rock layers and layering
• What does paleontology study?

  The life that existed prior to or at the start of the Holocene epoch
• What are the two methods scientists use to measure geologic time?

  • Relative dating
  • Absolute dating
• What is relative dating?

  • Places events or rocks in chronological order without knowing their actual age
  • Based on principles such as:
  • Original Horizontality
  • Superposition
  • Cross-cutting Relationships
  • Inclusions
• What is absolute dating?

  • Places actual ages of rocks and events
  • Based on the decay rate of radioactive isotopes
• How is the geologic time scale developed?

  • Based on the study of rocks' composition and structure
  • Analysis of rock layers and fossils
• What does the geologic time scale represent?

  • The interval time occupied by the geologic history of Earth
  • A meaningful time frame for arranging events of the geologic past
• What are the divisions of geologic time?

  • Eon
  • Era
  • Period
  • Epoch
• What is the significance of the Hadean Eon?

  • Earth's surface was bombarded by meteorites
  • Very hot mantle due to severe volcanism
  • Formation of the solar system from a cloud of dust and gas
• What significant events occurred during the Archean Eon?

  • Earth cooled enough for stable conditions
  • Photosynthesizing cyanobacteria appeared
  • Active volcanism added gas and water vapor to the atmosphere
  • Prokaryotes appeared
• What significant events occurred during the Proterozoic Eon?

  • Prokaryotes grew in abundance
  • First soft-bodied animals appeared
  • Mass extinction of anaerobic organisms
  • Formation of the ozone layer
  • Eukaryotes appeared
• What characterizes the Phanerozoic Eon?

  • Evidence of fossilized hard body parts of modern living things
  • Divided into Paleozoic, Mesozoic, and Cenozoic eras
• What are the periods of the Paleozoic Era?

  • Cambrian Period
  • Ordovician Period
  • Silurian Period
  • Devonian Period
  • Carboniferous Period
  • Permian Period
• What significant events occurred during the Cambrian Period?

  • Marine-shelled invertebrates appeared
  • First true animals (e.g., trilobites, jellyfish, first fishes) emerged
  • First fungi appeared
• What significant events occurred during the Ordovician Period?

  • Age of Invertebrates
  • First vertebrates appeared in the form of jawless fish
• What significant events occurred during the Silurian Period?

  • First land plants appeared
  • Appearance of vascular plants
• What significant events occurred during the Devonian Period?

  • Age of fishes with rapid diversification
  • First insects and amphibians appeared
  • Late Devonian Extinction (70% of all species wiped out)
• What significant events occurred during the Carboniferous Period?

  • Age of amphibians with first seed plants
  • First reptiles and large cartilaginous fishes appeared
  • Vast forest ecosystems and highest oxygen levels
  • Carboniferous Rainforest Collapse
• What significant events occurred during the Permian Period?

  • Formation of Pangaea
  • Origin of conifers
  • Permian-Triassic extinction event
  • Age of land vertebrates
• What are the periods of the Mesozoic Era?

  • Triassic Period
  • Jurassic Period
  • Cretaceous Period
• What significant events occurred during the Triassic Period?

  • Archosaurs and Therapsids began to repopulate
  • Dinosaurs and pseudosuchians became dominant land animals
• What significant events occurred during the Jurassic Period?

  • Pangaea separated into Laurasia and Gondwana
  • Appearance of sauropods, crocodiles, birds, and mammals
  • Birth of gymnosperms
• What significant events occurred during the Cretaceous Period?

  • Continents continued to drift apart
  • Marine predators dominated the sea
  • Angiosperms appeared
  • Extinction of dinosaurs
• What are the periods of the Cenozoic Era?

  • Tertiary Period
  • Quaternary Period
• What significant events occurred during the Tertiary Period?

  • First large mammals and primates appeared
  • Formation of present-day continents
  • Rise of angiosperms
• What significant events occurred during the Quaternary Period?

  • Earth's climate entered an ice age
  • Fluctuations in climate conditions
  • Homo sapiens evolved
• What significant events occurred during the Pleistocene Epoch?

  • Great ice age
  • Earliest humans appeared
• What significant events occurred during the Holocene Epoch?

  • Ice age ends
  • Humans became dominant
  • Current geological epoch
• What is the Anthropocene Epoch?

  An unofficial unit of geologic time describing the period when human activity significantly impacted the planet's climate and ecosystems