Lesson 2

• Scientists developed the geological time scale by studying rock layers and fossils worldwide.
• Eons


  The largest and most general division of time
• The Mesozoic era is known as the Time of Reptiles and saw the appearance of dinosaurs, mammals, and gymnosperms
• The Phanerozoic eon began 540 million years ago and is still continuing today
• Radioactive dating helped determine the absolute divisions in the time scale
• The Cenozoic era, from 65 million years ago to present days, saw the development of modern mammals, angiosperms, and human beings
• The Cryptozoic eon (Precambrian time) is the oldest and longest, covering almost 90% of Earth’s history
• The Geological time scale is a record of the life forms and geological events in Earth’s history
• CAMBRIAN EXPLOSION is the belief that there was a sudden, apparent explosion of diversity in life forms about 545 million years ago
• Fossils are evidences of organisms that lived in the past
• Law of Superposition: if a layer of rock is undisturbed, the fossils found on upper layers are younger than those found in lower layers of rocks
• The Six Ways of Fossilization

  • Unaltered preservation
  • Permineralization/ Petrification
  • Replacement
  • Carbonization or Coalification
  • Recrystalization
  • Authigenic preservation
• Fossils can be

  • Actual remains like bones, teeth, shells, leaves, seeds, spores
  • Traces of past activities such as animal burrows, nests, dinosaur footprints, ripples on a prehistoric shore
• In exceptional preservation, fine details such as original color and individual muscle fibers are retained, features often visible in electron microscopes. This is referred to as the “Medusa effect”
• The start of the Cambrian was characterized by the breaking up of supercontinent Gondwana into smaller land masses opening up new environmental niches where organisms can colonize and specialize
• Deleterious Mutations


  • Affect the phenotype and in turn, reduce the fitness of an organism and increase the susceptibility to several illnesses and disorders
• The Geologic time is divided into four large segments called Eons:


  1 Hadean eon

  2 Archean eon

  3 Proterozoic eon

  4 Phanerozoic eon
• The Phanerozoic eon is divided into Eras:

  1 Paleozoic era (Past Life)

  2 Mesozoic era (Middle Life)

  3 Cenozoic era (Present Life)
• Smaller divisions, called Periods, characterized by a single type of rock system, make up each Era.
• Some Periods are further divided into smaller time frame called Epochs
• The largest sections of the geological time scale are called “eons” that are divided into “eras” (the 2nd largest section).
• Eras are divided into “periods” that are divided into ‘epochs”.
• The eons are: -where both consists of three eras


  1 Cryptozoic (Precambrian) eon

  2 Phanerozoic eon
• Major eras in Earth’s history are:

  1 Archean era (4600 mya - 2500 mya)

  2 Proterozoic era (2500 mya - 540 mya)

  3 Paleozoic era (540mya - 250mya)

  4 Mesozoic era (250 mya - 65.5 mya)

  5 Cenozoic era (65.5 mya – present).
• Each Era is divided into even more specific blocks of time called periods where various geologic events are associated with each period.
• In this eon, Simple organisms like bacteria, algae, and protozoa was born and The oldest rocks that we know were found which dates to about 3.5 billion years old. 


  CRYPTOZOIC EON (PRECAMBRIAN TIME)
• Cryptozoic Era is divided into two eras:

  1 Proterozoic era

  2 Archean era
• In the Archean era, earliest plants (marine algae) were developed and the first life bacteria came into existence (3800 million years)
• In the Proterozoic era, Marine Invertebrates were probably common few with shells and glaciations took place, probably worldwide.
• The oldest rocks (3500 million years ago) were formed in the Archean era.
• The Palaeozoic era is divided into 6 periods:

  1 Permian period

  2 Carboniferous period

  3 Devonian period

  4 Silurian period

  5 Ordovician period

  6 Cambrian period
• In the Paleozoic era, organisms had hard parts (Shells, exoskeletons)
• In the Paleozoic era, evolution time and development of pteridophytes, amphibians, reptiles, fishes, wing bearing insects, trilobites etc.
• The Mesozoic era is divided into three periods:

  1 TRIASSIC PERIOD

  2 JURASSIC PERIOD

  3 CRETACEOUS PERIOD
• The Cenozoic era is divided into two periods:

  1 Tertiary period

  2 Quarterly period
• The Cambrian explosion created the complexity of multi-celled organisms in a relatively short time frame of 5 to 10 million years
• Type of fossil where impression made in a substrate = negative image of an organism, example: shell


  Molds
• type of fossil when a mold is fill in example: bones and teeth


  Casts
• type of fossil when organic material is converted into stone example: Petrified trees and coal balls


  Petrified fossils
• Fossilized plants and their tissues, in round ball shape

  Coal balls