Guide 1: Why crypto currency exists

Background:

The concept of 'money' has been part of human civilisation for over 10,000 years. 
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We have always wanted to trade one item for other items, but 'how' we trade has changed over time. 

For example:

10,000 BC:  People would trade one item they had, for another item they needed. Let's say they had lots of apples, and needed some corn - they would find someone who needed their apples, and had corn!
600 BC:  The first known 'currency' was introduced. Now people could trade gold, silver and bronze coins for apples and corn, knowing those coins could be useful to buy others items they needed at a later date. 
So, over the period of 9,500 years people still traded apples and corn, but how they did it changed.