Geological time scale

This task is about reading information from a geological time scale.
Use the Geological Time Scale to answer these questions.
geological-time-scale.png

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a)  What is the oldest 'Era' shown on this scale? 

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b)  What is the most recent 'Sub-era'?

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c)  How long did the Permian 'Sub-era' last?   million years 

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d)  A group of dinosaurs called Stegosaurs roamed the Earth between 188 and 65 million years ago.
    What was the main 'Sub-era' they lived in?

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e)  What does the z stand for in the abbreviation Pz?

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f)  Why do scientists use abbreviations for time periods?