Gen. Bio 2

• Earth has been around for billions of years and the way that scientists make an estimate is through the geologic time scale
• Geologic time scale


  A system of dating the history of Earth in a chronological manner using geological data
• The geologic time scale reflects the entire geological history of our planet
• Divisions of the geologic time scale

  • Eons
  • Eras
  • Periods
  • Epochs
• Phanerozoic Eon


  Means 'visible life' that was constructed through rock units that bear abundant fossils
• Precambrian Eon


  Represents the period between the birth of the planet and the appearance of life forms
• Divisions of the Precambrian Eon

  • Proterozoic
  • Archean
  • Hadean
• Divisions of the Phanerozoic Eon

  • Cenozoic era
  • Mesozoic era
  • Paleozoic era
• Cenozoic era


  Also known as the ' age of mammals '
• Mesozoic era


  Also known as the ' age of reptiles '
• Paleozoic era


  Also known as the ' age of invertebrates '
• Periods in the Paleozoic era

  • Cambrian
  • Ordovician
  • Silurian
  • Devonian
  • Carboniferous
  • Permian
• The periods in geological time scale from oldest to most recent are Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian, Triassic, Jurassic, Cretaceous, Tertiary, Quaternary
• 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 and tries 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
• The theory of spontaneous generation states the idea that life comes from lifeless or nonliving material through a mysterious process
• The theory of panspermia states that the building blocks of life come from outside Earth
• Present-day organisms share common ancestors that evolved through time. First life forms are believed to have emerged 3.7 billion years ago
• Based on movies, it is depicted to have unfavorable atmospheric conditions and a lot of active volcanoes that erupt from time to time which maintained a constant lava flow on Earth's surface during the Precambrian
• Divisions of the Precambrian Eon

  • Hadean
  • Archaean
  • Proterozoic
• During the Hadean, Earth's surface was in the form of liquid rock and boiling sulfur that built an ocean of hot materials
• During the Archaean, Earth's interior was still hot and active and this caused a series of volcanic eruptions. The continents have not formed yet during this time
• During the Proterozoic, Earth was suspected to have two supercontinents: one was located in the equator and the other one was situated on the other side
• The Paleozoic era spanned around 300 million years, which was almost half of the entire Phanerozoic. During this time, there were six major continental landmasses
• At the start of the Paleozoic era, the world-continent Pannotia was broken into pieces leading to the formation of Pangaea that makes Earth's continents connected once again
• The Paleozoic era is mainly characterized by the explosion of different life forms that started to emerge on Earth
• Periods in the Paleozoic era

  • Cambrian
  • Ordovician
  • Silurian
  • Devonian
  • Carboniferous
  • Permian
• During the Cambrian, the explosion of life occurred
• During the Ordovician, dominant animals were marine invertebrates such as trilobites and corals
• During the Silurian, it is marked by the first appearance of land plants
• During the Devonian, it is also known as the Age of Fishes
• During the Carboniferous, first seed plants and first reptiles appeared
• During the Permian, it is marked by the extinction of 90% of Earth's species
• Ediacarans appeared in the fossil record that was dated almost 600 million years ago during the Precambrian
• One of the important Ediacarans was the Dickinsonia, which resembles a ribbed doormat