Earth's interior is composed of a thick, semi-solid mantle, which surrounds a smaller, two-part core. The inner core is solid, and the outer core is liquid. Above the mantle lies the thin crust, which makes up the continents and the sea floor. Above the crust is the hydrosphere, which contains oceans, rivers, and lakes. The atmosphere lies above Earth's surface, and at much higher altitudes, a protective tear-shaped layer known as the magnetosphere surrounds Earth.