EARTH GEOLOGIC TIME SCALE

• Geologic time is divided into two eons. The more ancient eon is called the Precambrian, and the more recent is the Phanerozoic. 
• The Precambrian is a longest span of time in Earth's history, preceding the Cambrian Period and extending from the formation of the Earth around 4.6 billion years ago to approximately 541 million years ago. 
• The Precambrian eon is divided from most ancient into the Hadean eon, Archean eon, and Proterozoic eon. 
• Hadean Eon: 4.6 billion years ago to roughly 3.8 billion years ago.
• Hadeon: It's named after Hades, the ancient Greek god of the 

  underworld, due to the extremely 

  harsh conditions thought to have 

  prevailed on early Earth.
• Archean Eon: 3.8 – 2.5 billion years ago. 
• Archaen eon is characterized by the formation of the Earth's crust, 

  the emergence of early oceans, 

  and the development of 

  primitive life forms like bacteria 

  and archaea. 
• Proterozoic Eon: 2.5 billion years ago to 542 million years ago 

  • The Proterozoic Eon saw significant geological and 

  biological developments, 

  including the buildup of oxygen 

  in the atmosphere and the 

  proliferation of eukaryotic 

  organisms. 
• An eon that spans for three eras; namely Paleoproterozoic, 

  Mesoproterozoic and 

  Neoproterozoic 
• The Phanerozoic Eon is the most recent eon in Earth's history, and it's the one we're still in today. It started about 541 million years ago and continues to the present day. 
• The Phanerozoic eon is subdivided into three eras – the Paleozoic era, Mesozoic era, and Cenozoic era. An era is often divided into several smaller time spans called periods.
• The Paleozoic era; longest and diverse ● Permian Period 300-250 million years ago 

  ○ ⋆ all the major land masses collided to form the 

  supercontinent “Pangea” 

  ○ ⋆ temperature were extreme and climate was dry. 
• Carboniferous Period 350-300 million years ago ⋆ widespread forest of large plants left massive deposits of carbon that eventually turned coal and crude oil. 

  ○ ⋆ First amphibian evolve and lived in water and land 

  ○ ⋆ first reptile evolved. They were the first animals that can reproduce on dry land.
• Devonian Period 400-350 million years ago 

  ○ ⋆ first seed plant evolved. 

  ○ ⋆ Seed plants have a protective seed coat and stored food in their cotyledon to survive. 

  ○ ⋆Eventually, plants that bears seeds become the most 

  common type of plants in land 

  ○ ⋆ fish with lobe fins evolved. They could breath-in air out from water. 
• Silurian Period 450-400 million years ago 

  ○ ⋆ In the ocean corals appear and fish continuous to evolved, On land vascular plants evolve and 

  they grow bigger than the existing non-vascular plants. 
• Ordavician Period 500-450 million years ago 

  ○ ⋆ the oceans are filled with invertebrate animals. 

  ○ ⋆ Plants dominate the land while most of the animals remained in the water. 

  ○ ⋆ The first fish evolved
• Cambrian Period 550-500 million years ago 

  ○ ⋆ Following the precambrian mass extinction there was an explosion of new organisms in the cambrian period. 

  ○ ⋆ Sponges evolved and Small invertebrates like the trilobites were very abundant.
• The Mesozoic Era; Age of the Dinosaurs ● Cretaceous Period 150-65 million years ago 

  ○ ⋆ Dinosaurs reach their peak and distributions, and the continent 

  was close to the current position 

  as they are right now. 

  ○ ⋆ Earth’s climate is warm and poles lacked ice caps 

  ○ ⋆ Extinction of dinosaurs
•  Jurassic Period 200-150 million years ago 

  ○ ⋆ this is the golden age of the dinosaurs 

  ○ ⋆ whereas the dinosaurs’ species flourish. The earliest bird evolved 

  from reptile ancestors and major 

  group of mammals evolved while 

  individual mammals remain small 

  in size. 

  ○ ⋆ Flowering plants appear and new insects evolved to pollinate 

  the flowers. 
• Triassic Period 250-200 million years ago 

  ○ ⋆ The first dinosaurs branched off from the reptiles and they 

  colonized the land, water and air 

  ○ ⋆ Huge seed ferns and conifers dominated the forest. 

  ○ ⋆ Modern corals, fish and insects evolved. 

  ○ ⋆ Pangea started to separate into Laurasia. 
• Cenozoic Era 

  ● Divided into two periods : Tertiary and Quaternary. 

  ● A period is divided into an even smaller unit called an epoch. 
• The Tertiary period of the Cenozoic era comprises the Paleocene, Eocene, Oligocene, Miocene, and Pliocene epochs. 
• The Quaternary period of the Cenozoic era includes the Pleistocene and Holocene (recent) epochs.
• 1. Tertiary Period : 65- 0,01 million years ago 

  ● ⋆ During the Tertiary period, Earth’s climate was generally warm and humid. ● ⋆ Mammals evolved to fill virtually all niches vacated by dinosaurs. 

  ● ⋆ Many mammals increased in size. Mammals called primates evolved, including human ancestors. 

  ● ⋆ Modern rain forests and grasslands appeared, and flowering plants and insects were numerous and widespread. 
• Quaternary Period : 2 million years ago -present
• Quaternary Period : Halocene (present) : 0.01million years ago – present 
• Quaternary Period : Pleistocene : 2 – 0.01 million years ago 
• Quaternary Period : This created land bridges between continents, allowing land animals to move to new areas. 

  ● ⋆ Some mammals adapted to the cold by evolving very large size and thick fur. ● ⋆ The last ice age ended about 12,000 years ago. By that time, our own species, Homo sapiens, had evolved.
• Tertiary Period Pliocene : 5 – 2 million years ago, the first primates appeared.
• Tertiary Period Miocene : 25 – 5 million years ago 
• Tertiary Period Oligocene : 35 – 25 million years ago 
•  Tertiary Period Eocene : 55 – 35 million years ago
• Tertiary Period Paleocene : 65 – 55 million years ago 
• MESOZOIC ERA "AGE OF THE DINOSAURS"
• PALEOZOIC ERA " AGE OF THE FISH"
• PALEOZOIC ERA "AGE OF AMPHIBIANS"
• PRE CAMBRIAN "DEVOID OF OXYGEN"
• CENOZOIC ERA "AGE OF MAMMALS"
• MESOZOIC "AGE OF THE REPTILES"