When did the Phanerozoic era begin?  This is the same time a…

When did the Phanerozoic era begin?  This is the same time as the end of the Proterozoic, and the beginning of the Cambrian period.  Enter your result as millions of years.  For example: if you think the answer is 3.5 billion years ago, enter 3500.  Or if you think it’s 5 million years ago, enter 5.