Simplify the following text for a Grade 6 native English-speaking person.
Original: The Bering land bridge was a land bridge roughly 1,000 miles ( 1,600 km ) north to south at its greatest extent , which joined present-day Alaska and eastern Siberia at various times during the Pleistocene ice ages .
Simplified: Its greatest extension was about 1,000 miles ( 1,600 km ) north to south .