Introduction It is very difficult to obtain a time scale for the earth. This is because the earth is constantly changing To describe the sequence and length of these changes, scientists have developed a geological time scale.

 To create a timeline an indication of time must be available. This indication of time is called a geological column.  In a geological column we examine the different layers of rock to distinguish time.  The types of rocks and fossils within each layer inform us of the time period.

Divisions of Geological Time  Just like a calendar is divided into weeks, months and years so is the earth’s geological time scale  The history of the earth is punctuated by major events or changes on the earth’s surface and climate

Time Divisions  There are three divisions of time: 1) Eras 2) Periods 3) Epochs

ERAS  A very large unit of time, can span many millions or even billions of years  Four eras include: Precambrian time, Palaeozoic Era, Mesozoic Era, and Cenozoic Era

PERIODS  A smaller period of time  Characterized by the specific fossils or named for a location where fossils were first found  Example: Devonian Period- Devonshire, England

Epochs  The smallest unit of time used to measure the geological time scale  Used to divide up larger periods

Mesozoic Era  Began 248 million years ago and lasted until 65 million years BC  During this era, Pangaea was forming the earth  The conditions on the earth that Pangaea created favoured the survival of reptiles.

During this era, Pangaea was forming the earth. The conditions on the earth that Pangaea created favoured the survival of reptiles.

Periods  The Mesozoic era is divided into three smaller periods 1) Triassic 2) Jurassic 3) Cretaceous

Triassic Period  Dinosaurs first appeared on earth  Dinosaur is the Greek word for “terrible lizard”  They ranged in size from the size of a squirrel up to the size of ten bulls.

Jurassic Period  Dinosaurs became the dominant life form  Two types of dinosaurs developed: 1) Saurischians- “lizard hipped” included herbivores and carnivores (Apatasaurus) 2) Ornithischians- “bird hipped” (stegosaurus)

Saurischian- Apatasaurus Ornithischians- Stegasaurus

Cretaceous Period  Dinosaurs continue to reign  Exponential plant growth and evolution  The first angiosperm appear (flowering plants)  Marks the end of the Mesozoic Era  Mass extinctions

Extinction Theories  1) Asteroid impact 2)Climate change due to Pangaea