earths timeline

• So far, Earth is the only planet known to support life. The mere presence of life forms on Earth sets it aside from the other known planets in the universe.
• Scientists started to formulate a series of theories regarding the emergence of life forms on the planet and relate it to the physical changes on Earth's environment.
• Geologic time scale


  A system of dating the history of Earth in a chronological manner using geological data

  
• Units of the geologic time scale

  • Eon
  • Era
  • Period
  • Epoch

  
• Eon


  The largest unit of time
• Era


  A unit of time shorter that an eon but longer than a period
• Period


  A unit of time shorter than an era but longer than epoch
• Epoch


  A unit of time shorter than a period but longer than an age
• The Phanerozoic Eon (542 MYA) means 'visible life' that was constructed through rock units that bear abundant fossils.
• The Precambrian Eon (4 BYA) represents the period between the birth of the planet and the appearance of life forms.
• Eons


  • Phanerozoic
  • Precambrian
• Eras in the Phanerozoic Eon

  • Cenozoic
  • Mesozoic
  • Paleozoic
• The Cenozoic era is also known as the 'age of mammals', the Mesozoic era is also known as the 'age of reptiles', and the Paleozoic era is also known as the 'age of invertebrates'.
• Periods in the Cenozoic Era

  • Quaternary
  • Tertiary
• Periods in the Mesozoic Era

  • Cretaceous
  • Triassic
  • Jurassic
• Periods in the Paleozoic Era

  • Carboniferous
  • Silurian
  • Devonian
  • Permian
  • Cambrian
  • Ordovician

  
• Epochs are the shortest subdivision unit in the Earth's geologic time scale that is characterized by the changes in life forms and may vary from continent to continent.

  
• The most important time period for the emergence of diverse life forms on Earth is the Phanerozoic Eon.

  
• Theories on the origin of life on Earth

  • Spontaneous generation theory
  • Primordial soup theory
  • Theory of panspermia
• Spontaneous generation theory


  The idea that life comes from lifeless or nonliving material through a mysterious process
• Pasteur's experiment disproved spontaneous generation.
• Theory of panspermia


  The building blocks of life came from another planet
• Primordial soup theory


  Life started in a primordial soup of organic molecules, trying to explain how catalysts for nonliving things became living cells
• One of the earliest known evidence of life on Earth includes the stromatolite fossils collected from various samples of metasedimentary rocks in western Greenland and were aged 3.7 billion years old.
• In 2015, fossils of the microbial mat (primitive microbial colony) that may represent potential biotic life dated 4.1 billion-year-old were collected in Western Australia.
• If speciation during the Cambrian period did not occur, modern-day organisms would not have emerged.
• Present-day organisms share common ancestors that evolved through time. First life forms are believed to have emerged 3.7 billion years ago.