Simplify the following text for a Grade 8 native English-speaking person.
Original: The fourth millennium is a period of time that will begin on January 1 , 3001 , and will end on December 31 , 4000 , of the Gregorian calendar .
Simplified: The 4th millennium is a period of time that will start on January 1 , 3001 and end on December 31 , 4000 .