Geologic Time Scale

• Geologic Time Scale is a record of the life forms and geological events in Earth’s history.
• Scientists developed the timescale by studying rock layers and fossils worldwide.
• UNIFORMITARIANISM

  • The idea that the same geologic processes shaping the earth today have been at work

  throughout history.

  ● Erosion

  ● Deposition

  ● Movement of Lithospheric Plates

  ● Changes in atmosphere
• CATASTROPHISM

  The principle that states that all geologic changes occur

  suddenly.

  • Through catastrophes such as:

  ● Impact of an asteroid or comet

  ● Earthquakes
• PALEONTOLOGY

  ● The science involved with the study of

  a past life.

  ● The data used for this study of a past

  life are fossils.
• FOSSILS Are the remains and traces of plants

  and animals that have lived and died

  through-out earth’s History and are

  preserved in rocks.
• COMMONLY PRESERVED: shells, bones,

  hard parts of insects, woody materials
• RARELY PRESERVED: skin, internal organs,

  hair, feathers
• EON: largest division of time. Containing two or more Era.
• ERA: a defined period of time with a start event and an end event.
• PERIOD: form a division which geologists use to divide earth’s history,
• EPOCH: a division of time that is no longer than an age, but shorter than a period.
• ARCHEAN EON (3.8-2.5 Ga)

  1. Anaerobic (lack of oxygen)

  b. No Ozone

  c. Photosynthetic prokaryotes (blue-green algae) emerged and started releasing oxygen

  to the atmosphere

  d. Life forms still limited to single-celled organisms without a nucleus (prokaryotes)

  until 2.7 Ga when eukaryotes emerged.
• PROTEROZOIC EON (2.5 Ga to 540 Ma)

  1. Oxygen level reaches ~3% of the atmosphere

  b. Rise of multicellular organisms represented by the Vendian fauna

  c. Formation of the protective Ozone Layer
• PHANEROZOIC EON (540 Ma to PRESENT)

  1. Eon of “visible life”

  b. Diversification of life. Many life forms represented in the fossil record

  c. Life forms with preservable hard parts
• PRECAMBRIAN ERA

  Covers approximately 80% of earth’s history

  3.4 Billion years ago: Microscopic Bacteria

  Atmosphere: water vapor, CO2, Nitrogen, No oxygen, Ozone layer protects from UV

  Later primary plants evolved, used photosynthesis which created oxygen.

  • Oxygen accumulates 2.5 billion years ago
• FIRST FOSSIL

  STROMATOLITES

  –Oldest evidence

  –Calcium carbonate (material

  deposited by algae)

  –They are formed by layers of

  cyanobacteria.

  –600 million years ago : 1st

  multi-celled animals
• PALEOZOIC ERA

  544 million years ago... lasted 300 million years.

  Explosion of life in the oceans began during this era.

  • This era opened with the breakup of the world continent Rodinia and closed with

  the formation of Pangea, as the Earth’s continents came together once again.
• CAMBRIAN PERIOD (AGE OF THE TRILOBITES)

  • Appearance of all invertebrates Dominance of trilobites and brachiopods
• TRILOBITES- lived in Earth’s ancient seas. Extinct before the dinosaurs came into existence
• BRACHIOPODS- marine animals that resemble clams.
• ORDOVICIAN PERIOD

  • Appearance of invertebrates. Early fish did not have jaws. Some species of sharks

  were in existence at this time. (Didymograptus murchisoni)
• SILURIAN PERIOD

  • Invasion of fishes, arthropods, and land plants including mosses, ferns, and

  cone-bearing plants (crinoid)
• DEVONIAN PERIOD (AGE OF FISHES)

  First insect fossils

  First trees

  Fish dominate

  • First amphibians (tiktaalik

  rosae)
• CARBONIFEROUS PERIOD

  “Age of Amphibians” - “The Coal Age”

  • Amphibians became abundant in large coal swamps
• PERMIAN PERIOD

  • Extinction of trilobites and other marine animals. First reptiles appeared

  ➢ At the end of the Paleozoic, the largest mass extinction in history wiped out

  approximately 90% of all marine animal species and 70% of land animals.

  ➢ Climate became seasonal
• POSSIBLE CAUSES OF THIS MASS EXTINCTION EVENT

  ❖ Lowering of sea levels when the continents were rejoined as Pangea

  (convergent boundary)

  ❖ Increased volcanic activity (ash & dust)

  ❖ Climate changes- cooler climate
• MESOZOIC ERA

  • At the beginning of this era, the continents were joined as Pangea
• TRIASSIC PERIOD

  • “Age of reptiles” became the most abundant animals because of their ability to adapt to the drier climate of the Mesozoic Era
  • First small dinosaurs dominate (keichousauros hui)
• JURASSIC PERIOD

  Reptiles dominant in sea, air, and land

  Larger and more abundant dinosaurs appeared

  First birds

  Pangea broke up around this period.

  • Small mammals and birds also appeared during this era.
• CRETACEOUS PERIOD

  Dominance of flowering plant

  Extinction of large reptiles and ammonites

  The main plant life of this time were Gymnosperms

  • Flowering plants appeared during this era.

  ➢ This era ended with a mass extinction event about 65 million years ago.

  ➢ Many groups of animals including the dinosaurs disappeared suddenly at this time.

  ➢ Many scientists believe that this event was caused by a comet or asteroid colliding

  with the earth.
• WHAT ARE THE EFFECTS OF FALLING COMETS AND ASTEROIDS?

  ❖ Huge cloud of smoke and dust fills the air

  ❖ Blocks out sunlight

  ❖ Plants die

  ❖ Animals that eat plant-eaters die.

  ❖ Animals that eat plants die
• However, not all forms of life died during this event. Many animals that you see today are

  descendants from the survivors of this extinction event.
• CENOZOIC ERA

  • 65 million years ago...continues through present day
• TERTIARY PERIOD

  “Age of Mammals”

  Rise of birds and placental mammals

  • During the Pliocene, the first hominids appeared: these were our human

  ancestors.
• QUATERNARY PERIOD

  “Age of Humans” dominance of human

  Modern species of mammals

  • Extinction of large forms such as mammoth

  ➢ Humans are thought to have appeared around 3.5 million years ago.

  ➢ Today we are in the Holocene Epoch of the Quaternary Period of the Cenozoic

  Era.

  ➢ The age of the Earth is about 4.54 billion years ago as of 2019.

  ➢ Humans appeared in the fossil record around 66 million years ago