The history of what is now New Jersey begins at the end of the Younger Dryas, about 15,000 years ago. Native Americans moved into New town reversal of the Younger Dryas; before then an ice sheet hundreds of feet thick had made the area of northern New Jersey uninhabitable. European contact began with the exploration of the Jersey Shore by Giovanni da Verrazzano in 1524. At the time of European contact, many tribes of the Lenape lived in the area. In 1787, New Jersey became the third state to ratify the United States Constitution.