ch_9_notes[Conflict].notebook April 07, 2016

A View of Earth's PastObjectives • ES.7.a.4: Identify that Paleozoic, Mesozoic, and Cenozoic

fossils are found in Virginia.• ES. 7.a.5: Describe how life has changed and become more

complex over geologic time.• ES.7.a.11: Analyze the impact and role of global catastrophes

(including asteroid/comet impacts, volcanism, continental collisions, and climate collapse) on extinctions and evolution.

• ES.7.a.10: Define components of the geologic time scale (eon, era, period, and epoch).

ch_9_notes[Conflict].notebook April 07, 2016

What might have taken place on Earth during its more than 4­billion­year

history?

With your partner, discuss...

Key terms:• Geologic column: an ordered arrangement

of rock layers that is based on the relative ages of the rocks and in which the oldest rocks are at the bottom.

• Era: a unit of geologic time that includes two or more periods

• Period: a unit of geologic time that is longer than an epoch but shorter than an era.

• Epoch: a subdivision of geologic time that is longer than an age but shorter than a period

ch_9_notes[Conflict].notebook April 07, 2016

• History of the Earth is divided into units based upon the fossils contained within the rocks.

• Four units of time are used:> Eon (longest amount of time)> Era> Period> Epochs (shortest amount of time)

Checkpoint: How do we subdivide geologic time?

ch_9_notes[Conflict].notebook April 07, 2016

• Eon­­longest time period; measured in billions of years> Archean Eon ­­ Beginning of life> Proterozoic Eon ­­ Early life> Phanerozoic Eon ­­ Current Eon

• Era­­measured in millions to billions of years; defined by differences in life forms found in rocks> Paleozoic Era: "Paleo" old "zoic" life; ended with a large

extinction> Mesozoic Era: "Meso" middle "zoic" life; began with the

emergence of dinosaurs and ended with the extinction of dinosaurs

> Cenozoic Era: "Ceno" recent "zoic" life; emergence of mammals

What_is_the_Cenozoic_Era_.asf

What_is_the_Mesozoic_Era_.asf

What_is_the_Paleozoic_Era_.asf

ch_9_notes[Conflict].notebook April 07, 2016

• Periods­­defined by life forms that were abundant or became extinct during the time in which the rocks were deposited; measured in tens of millions to hundreds of millions years ago> characterized by specific fossils> usually named for location in which fossils were first

discovered

• Cambrian (oldest)• Ordovician• Silurian• Devonian• Carboniferous (Mississippian & Pennsylvanian)• Permian• Triassic• Jurassic• Cretaceous• Tertiary• Quaternary (most recent)

How is a geologic period defined?

ch_9_notes[Conflict].notebook April 07, 2016

• Epochs: smallest unit of geologic time; measured in millions to tens of millions of years> different groups of organisms are used to distinguish

between epochs> may be divided into smaller units of time called ages

• Paleocene• Eocene• Oligocene• Miocene• Pliocene• Pleistocene• Holocene (current epoch)

All occur during Cenozoic Era

Precambrian time is the longest geologic time span in Earth's history. It is poorly represented because very few fossils exist from the unit of geologic time.

Forests and swamps that contributed vegetation to the deposits covered large areas

1. The division of periods into epochs depends in part on the richness of the fossil record. Why would it be easier to divide more recent periods into epochs than to divide earlier periods?

2. How many millions of years ago did Earth's atmosphere attain the oxygen levels it has today?

3. What is the longest geologic time span in Earth's history? Why is it so poorly represented in this table?

4. The fossil fuels we use today formed during the Carboniferous Period. What characteristics of the time period most likely contributed to the formation of these deposits?

More recent rocks have been altered or eroded less than older rocks have and are closer to the surface, so studying the fossils in younger rocks is easier.

488 million years ago

Get a textbook.

Turn to page 213.

Answer the questions on

your notes page.