Download 4.5 Notes “What is the geologic time scale?” Objective: Read and

4.5 Notes
“What is the geologic time scale?”
Objective: Read and interpret the geologic time scale.
The oldest rocks on Earth
are 4 billion years old. Based
on the age of Moon and Earth
rocks, scientists think Earth is
about 4.6 billion years old.
About how old is Earth?
By studying rocks and fossils, the geologic time scale was
developed. The geologic time scale outlines the major divisions
and kinds of organisms that lived in Earth’s history. The scale
begins when Earth was formed and goes to present day.
What is the geologic time scale?
Geologic time is divided into units, like the year is divided into
months, weeks, and days. The major unit is an era. Eras last
millions of years. There are four eras, which are divided into
periods. Periods are divided into epochs.
What are the divisions of geologic time?
Divisions in geologic time
are based on important
changes on Earth. The
extinction of a group of
organisms and the
appearance of a new
group of animals is a
division of geologic time.
The Diversity of Life:
Natural disasters and
changes such as volcanic
eruptions and ice ages
can cause mass
extinction. Biodiversity
keeps natural cycles on Earth running smoothly.
How do pollution and the spread of civilization threaten
biodiversity?