The Geological Time Scale
•	The Geological time scale is a record of the life forms and ___________________events in Earth’s history.  
•	Scientists developed the time scale by studying _________________ (strata) and fossils.
•	________________ dating helped determine the absolute divisions in the time scale.

Divisions of Geologic Time
•	Eons are divided into ___________________
•	Eras are subdivided into _____________...periods are subdivided into ______________.

FOUR  Eras…
•	__________________Era – 88% of earth’s history

•	___________________Era -544 million years ago…lasted 300 million yrs

•	__________________ Era - 245 million years ago…lasted 180 million yrs

•	__________________ Era - 65 million years ago…continues through present day

•	Geological time begins with _______________ Time.  Precambrian time covers approximately 88% of Earth’s history.

•	Today we are in the _______________Era.

Paleozoic Era (Ancient Life)
•	The _________________ period is the 1st period of the Paleozoic Era. 
•	The first multicelled organisms formed (____________________)
•	Known as the “Age of the _________________”
•	Explosion of life in warm, shallow seas began – fish too!

•	At the end of the _____________________, the largest mass extinction in history wiped out approximately 90% of all marine animal species and 70% of land animals.

        This was called the ____________________ extinction.
Trilobites
•	Lived in Earth’s ancient _____________
•	Extinct before the __________________ came into existence
•	Cambrian Period is know as the “Age of the ____________________”

Mesozoic Era (Middle Life)
•	__________________ broke up around the middle of the Mesozoic era.

•	_____________________became the most abundant animals because of their ability to adapt to the drier climate of the Mesozoic Era.
	
•	_______________________ were also very active in the Mesozoic Era.
•	Small mammals and birds also appeared during the Mesozoic Era.
–	The mammals were small, _____________________ animals with hair covering their bodies.
•	The main plant life of this time were _______________________ or plants that produce seeds, but no flowers. For example: ________________trees

•	_____________________ plants appeared during the END of this era.

•	The Mesozoic Era ended with a mass ______________ 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 ________________ or _______________colliding with the Earth.

Mesozoic Era’s Mass Extinction Event
•	Cause:  Asteroid or Comet collides with Earth.
•	Effect:
•	Huge cloud of ______________ and ____________ fills the air
•	Blocks out _________________
•	Plants die
•	Animals that eat plants die
•	Animals that eat plant-eaters die.

•	However, _________ 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 – Recent Life
•	Began about _________________ years ago and continues today!!!!!
•	Climate was warm and mild.
•	______________ animals such as whales and dolphins evolved.

•	Mammals began to increase and evolve _________________ that allowed them to live in many different environments – land, air and the sea.
•	Grasses increased and provided a food source for ____________ animals

•	This era is sometimes called the “Age of ____________________”

•	Humans are thought to have appeared around _____________ years ago (during the most recent ________________ – Quaternary).

•	________________ plants are now the most common plant life.