Temps Géologiques

Geological times

• Definition:
  The geologic time scale is a chronological classification system used to date events in the Earth's history. It begins with the formation of the Earth 4,6 billion years ago. The eras and geological periods correspond to the appearances and extinctions of the large groups.

1. Precambrian period: 4,6 bya → 541 mya
   

• It is the earliest part of Earth's history that is subdivided into three eons (Hadean, Archean and Proterozoic) of the geologic time scale
  
• 3,8 bya: Life appears in oceans: PROKARYOTES (unicellular organisms)
• 3,2 bya: Cyanobacteria are the first organisms able to create photosynthesis. They produced dioxygen (O2) which has been released in the atmosphere (creation of a protective ozone layer)
• 2,3 bya: Atmosphre becomes oxygen-rich
• 2,1 bya: EUKARYOTES appear (organism whose cells have a cell nucleus and other organelles enclosed within membranes)
• 1,5 bya: MULTICELLULAR LIFE appears (organisms that consist of more than one cell)
• 700 mya: FRIST ANIMALS in precambian oceans
  

1. Paleozoic period: (Cambrian) 541 mya → 252 mya
   

• It is the time when most of the major groups of animals first appear in the fossil record (divided in 6 periods: Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian)
  

• 530 mya: Cambrian Explosion: Almost all body organization plans appear
• 450 mya: First PLANTS = first land ecosystems
• 380 mya: First VERTEBRATE LAND ANIMALS AND ARTHROPODES (characterized by a segmented body that constitutes their exoskeleton) are amphibia

→Mass extinction

• These amphibia evolve into:

• First fish
  →Mass extinction
• Insects
• Reptiles
  →Mass extinction (96% of spices)

1. Mesozoic period: (Cambrian) 252 mya → 66 mya
   

• It is also called the Age of Reptiles (subdivided into three major periods: Triassic, Jurassic, and Cretaceous)

• 248 mya: First MAMALS 
• 230 mya: First DINOSAURS + First BIRDS

→Complete extension of dinosaurs 66 mya

1. Cenozoic period: (Cambrian) 66 mya → today
   

• It is the current geological era. It is also known as the Age of Mammals, because of the large mammals that dominate it (divided in é periods: Tertiary and Quaternary)

• Expansion of mammals, birds and insects
• 36 mya : First MONKEYS
• 1,8 mya : Glacial ages : HOMOSAPIENS appear
• 0,01 mya : Human civilisation

→Only dinosaurs completely disappeared, other species developed