Unit 3: Section 4: Topic: Geologic Time Scale

What is the geologic time scale? 

The geologic time scale is a record of the geologic events and life forms in Earth’s history.

How old is the Earth?

4.6 billion years old, or usually shown on the geologic time scale as 4600 million years old.  4600 million is equal to 4.6 billion (4,600,000,000).  Geologist used radioactive dating to determine the age of the Earth.

How is the geologic time scale divided?

The largest intervals are eons, with each eon composed of many millions of years. Within the eons are eras, which begin and end with dramatic changes in the types of plants and animals living on earth.

What eon did the T-Rex live?

Phanerozoic - meaning visible life

What eon do we live in?

Phanerozoic

What are eras?

Eras are a major division on the geologic time scale that breakdown eons by profound worldwide changes in life forms.

What era did T-Rex live?

during the Mesozoic Era (245 - 66.4 million years ago)

What era are we living in now?

Cenozoic era (66.4 million years ago - present)

What are periods?

Periods are a subdivision of an era in geologic time.

What period did T-Rex live?

Cretaceous (144 - 66.4 million years ago)

What period do we live in now?

Quaternary (1.6 million - present)

What are epochs?

An epoch is a subdivision of a period in geologic time associated mainly the Cenozoic Era.

What epoch did T-Rex live?

Late. There were no epochs before the Cenozoic era.  Geologist use early, middle, and late.

What epoch do we live in now?

We live in the Holocene epoch (0.01 million years ago - present).