Earth'S Crust Worksheet printable pdf download

Earth’s Crust

Name: _________________________________________________________ Period: ______ Date: ____________

crust

Earth has three layers: the crust, the mantle, and the core. The

is made of solid rocks and minerals. Beneath the crust is

mantle

the

, which is also mostly solid rocks and minerals, but punctuated by malleable areas of semi-solid magma. At the

core

center of the Earth is a hot, dense, mostly iron and nickel

Earth’s layers constantly interact with each other, and the crust and upper portion of the mantle are part of a single

geologic unit called the lithosphere. The lithosphere’s depth varies, and the Mohorovicic discontinuity (the Moho)—

the boundary between the mantle and crust—does not exist at a uniform depth. Isostasy describes the physical, chemical, and

mechanical differences between the mantle and crust that allow the crust to “float” on the more malleable mantle.

Earth’s crust is divided into two types: oceanic crust and continental crust. The transition zone between these two types of

crust is sometimes called the Conrad discontinuity. Silicates (mostly compounds made of silicon and oxygen) are the most

abundant rocks and minerals in both oceanic and continental crust.

Oceanic crust, extending 5-10 kilometers (3-6 kilometers) beneath the ocean floor, is mostly composed of different types of

basalts

. Oceanic crust is dense, almost 3 grams per cubic centimeter (1.7 ounces per cubic inch).

Oceanic crust is constantly formed at mid-ocean ridges of the Atlantic Ocean, where tectonic plates are tearing apart or

diverging from each other. As magma that wells up from these rifts in Earth’s surface cools, it becomes young oceanic crust.

The age and density of oceanic crust increases with distance from mid-ocean ridges.

Just as oceanic crust is formed at mid-ocean ridges, it is destroyed in subduction zones. Subduction is the important geologic

process in which a tectonic plate made of dense lithospheric material melts or falls below a plate made of less-dense

lithosphere at a convergent plate boundary.

At convergent plate boundaries between continental and oceanic lithosphere, the dense oceanic lithosphere (including the

crust) always subducts beneath the continental. In the northwestern United States, for example, the oceanic Juan de Fuca plate

subducts beneath the continental North American plate. At convergent boundaries between two plates carrying oceanic

lithosphere, the denser (usually the larger and deeper ocean basin) subducts. In the Japan Trench, the dense Pacific plate

subducts beneath the less-dense Okhotsk plate.

As the lithosphere subducts, it sinks into the mantle and melts, becoming more plastic and ductile. Through mantle convection,

the rich minerals of the mantle may be ultimately “recycled” as they surface as crust-making lava at mid-ocean ridges

and volcanoes.cLargely due to subduction, oceanic crust is much, much younger than continental crust. The oldest existing

oceanic crust is in the Ionian Sea, part of the eastern Mediterranean basin.

granites

Continental crust is mostly composed of different types of

. The continental crust is thicker but slightly less dense

(about 2.7 grams per cubic centimeter (1.6 ounces per cubic inch).

As with oceanic crust, continental crust is created by plate tectonics. At convergent plate boundaries, where tectonic plates

crash into each other, continental crust is thrust up in the process of orogeny, or mountain-building. For this reason, the

thickest parts of continental crust are at the world’s tallest mountain ranges. Like icebergs, the tall peaks of the Himalayas and

the Andes are only part of the region’s continental crust—the crust extends unevenly below the Earth as well as soaring into the

atmosphere.

Earth'S Crust Worksheet