Iapetus Ocean
During the Paleozoic Era, the tectonic plate containing the continent of Laurentia and the plate containing the continent of Gondwanaland were converging, the Iapetus Ocean that separated the two continents gradually closed, and the resulting collision between the plates formed the Appalachian Mountains. During the early stages of this mountain building known as the Taconic orogeny, a piece of ocean crust from the Iapetus Ocean broke off and became incorporated into the collision zone and now forms the oldest bedrock strata of Staten Island, the serpentinite.