Time Periods

_______________ is the long span of time that begins geologic time.

• Precambrian Time
• Cenozoic Time

A unit of geologic time that subdivides eras

• period
• time span

The Triassic Period, the Jurassic Period, and the Cretaceous Period occurred in what era?

• Cenozoic
• Mesozoic

_________ for many of the geologic periods come from places around the world where geologists first described the rocks and fossils of the period.

•  time
• names

Scientists chose where units of geologic time began on major changes in ______________ at certain times.

• life forms
• events

Scientists divided the time between Precambrian Time and the present into three units of time, or eras.

• True
• False

To develop the geologic time scale, scientists studied rock layers and fossils from the different eras. 

• True
• False

Eras are subdivided into units of geologic time called periods.

• True
• False

___________ a record of the geologic events and the evolution of life forms as shown in the fossil record. 

• Eras
• Geologic Time Scale

 The Quaternary period, where humans first appeared, is in the Mesozoic era.

• True
• False