Simplify the following text for a Grade 9 native English-speaking person.
Original: It is believed that the Narrows were most likely formed after deposition of the Harbor Hill Moraine about 18,000 years ago just before to the end of the last ice age . .
Simplified: The Narrows were most likely formed after deposition of the Harbor Hill Moraine about 18,000 years ago prior to the end of the last ice age .