EARTH'S FOUR LAYERS

                    EARTH'S FOUR LAYERS

Earth has four major layers. The crust floats on the mantle and is the thinnest and least dense of the four layers. The crust of the ocean floors ranges from 2 to 7 miles thick and is composed of igneous rock rich in iron and magne- sium. Continental crust ranges from 6 to 45 miles thick-it is thickest under mountain ranges-and contains much feldspar and silica, making it less dense than oceanic crust Over millions of years the crust has been shaped into a variety of landscapes, including both continental and oceanic mountain ranges and deep oceanic trenches. Earth's mantle is denser rock that extends about 1,790 miles toward the core. The mantle incorporates both brit- tle and molten layers. Temperature and pressure increase with the depth of the mantle .Earth's core lies beneath the mantle in two layers. The outer core, which is liquid, measures about 1,400 miles thick. The nier core, which is solid, lies at the center of isaherical, with only a 750-mile radius. Iron is the most common element in the outer and inner cores.the core and mental  are nearly the same thickness, yet the The core  mantle comprises 84 percent of Earth's volume and the core only 15 percent