How and when was the earth divided?
This occurred during Peleg’s life. Peleg was Shem’s son, and his name means “to divide or to split”. (See Strong’s Concordance Hebrew word H6389.) The division of the earth here refers to the division and dispersion of humanity that happened during the construction of the Tower of Babel. Genesis 11:1, 4, 6-9 (NIV), “Now the whole world had one language and a common speech. … 4 Then they said, “Come, let us build ourselves a city, with a tower that reaches to the heavens, so that we may make a name for ourselves; otherwise we will be scattered over the face of the whole earth.” … 6 The LORD said, “If as one people speaking the same language they have begun to do this, then nothing they plan to do will be impossible for them. 7 Come, let us go down and confuse their language so they will not understand each other.” 8 So the LORD scattered them from there over all the earth, and they stopped building the city. 9 That is why it was called Babel–because there the LORD confused the language of the whole world. From there the LORD scattered them over the face of the whole earth.”
As the Bible records, during the building of Babylon, God dispersed mankind around the earth and confused their languages. The people were divided into different languages.