Elements that make up Earth's crust include silicon, aluminum, iron, calcium, sodium and magnesium. Oxygen is also present and bonds with these other elements to create oxides. Oxygen is the most abundant element in the crust, followed by silicon. These elements form rocks and minerals.
Silicon, whose atomic number is 14, is a semimetallic, dark gray element with a blue tint. It's not found in a free state but in silicates and oxides, such as sand, quartz and flint.
Aluminum is a bright, silvery metal whose atomic number is 13. Like silicon, it's not found in a free state and needs to be extracted from ores, such as bauxite. Though it's soft, it gains strength when it's alloyed with other metals, such as copper and silicon.
Though iron, with atomic number 26, is renowned for its toughness and strength, it also rusts easily. However, it is used to make a variety of super-strong alloys.
Of the three major layers of Earth, the crust is the outermost and also the thinnest. Some scientists believe that the continental crust is only between 6 and 47 miles deep, and the oceanic crust is even thinner, only about 4 miles deep. In general, the oceanic crust is also younger than the continental crust.