A antonym for biosphere is an environment that is not natural.
Surface of the Earth: Most of the Earth's surface (70%) is covered with water, and the remaining 30% is taken up by the seven continental landmasses. However, underneath the water that fills the oceans, and the dirt and plants that cover the continents, the Earth's surface layer is made of rock.
Wikipedia says that the largest major plate is the Pacific, and that the smallest minor plate is Juan de Fuca. So that must be the correct answer after all.
They live near the United Startes because northern Canada is mostly ice and water
