Continental Crust | Composition, Density, & Facts | Britannica

Ask the Chatbot Games & Quizzes History & Society Science & Tech Biographies Animals & Nature Geography & Travel Arts & Culture ProCon Money Videos continental crust

• Introduction
• Composition
• Formation

References & Edit History Related Topics Images & Videos Contents Geography & Travel Physical Geography of Land print Print Please select which sections you would like to print:

• Table Of Contents

CITE verifiedCite While every effort has been made to follow citation style rules, there may be some discrepancies. Please refer to the appropriate style manual or other sources if you have any questions. Select Citation Style MLA APA Chicago Manual of Style Copy Citation Share Share Share to social media Facebook X URL https://www.britannica.com/science/continental-crust Feedback External Websites Feedback Corrections? Updates? Omissions? Let us know if you have suggestions to improve this article (requires login). Feedback Type Select a type (Required) Factual Correction Spelling/Grammar Correction Link Correction Additional Information Other Your Feedback Submit Feedback Thank you for your feedback

Our editors will review what you’ve submitted and determine whether to revise the article.

External Websites

• Frontiers - The Evolution of the Continental Crust and the Onset of Plate Tectonics

continental crust geology Ask Anything Homework Help Written and fact-checked by Britannica Editors Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree.... Britannica Editors History Britannica AI Ask Anything Table of Contents Table of Contents Ask Anything

continental crust, the outermost layer of Earth’s lithosphere that makes up the planet’s continents and continental shelves and is formed near subduction zones at plate boundaries between continental and oceanic tectonic plates. The continental crust forms nearly all of Earth’s land surface.

Composition

Continental crust is broadly granitic in composition and, with a density of about 2.7 grams per cubic cm, is somewhat lighter than oceanic crust, which is basaltic (i.e., richer in iron and magnesium than granite) in composition and has a density of about 2.9 to 3 grams per cubic cm. Continental crust is typically 40 km (25 miles) thick, while oceanic crust is much thinner, averaging about 6 km (4 miles) in thickness.

The effect of the different densities of lithospheric rock can be seen in the different average elevations of continental and oceanic crust. The less-dense continental crust has greater buoyancy, causing it to float much higher in the mantle. Its average elevation above sea level is 840 metres (2,750 feet), while the average depth of oceanic crust is 3,790 metres (12,400 feet). This density difference creates two principal levels of Earth’s surface.

Formation

Continental crust is formed primarily at subduction zones. Lateral growth occurs by the addition of rock scraped off the top of oceanic plates as they subduct beneath continental margins (the submarine edge of the continental crust). These margins are marked by lines of volcanoes, often in volcanic arcs, that form additions to the crust. Subduction zones located within ocean basins (where one oceanic plate descends beneath another) also generate volcanic arcs called island arcs. Island arcs are made up of materials that range between oceanic and continental crust in both thickness and composition. The first continents appear to have formed by accretion of various island arcs.

Related Topics: continental shield craton paraplatform Australian Shield platform (Show more) See all related content

There is also evidence that continental crust is formed through an accretionary process known as relamination. As an oceanic plate subducts underneath a continental plate, it pulls ocean floor sediment, magma, and larger concentrations of rock along with it. As pressure and temperature increase with depth, the rocks melt, and denser material within the descending oceanic plate continues to sink downward while less-concentrated silica-rich material forms granulites that adhere to the bottom of the continental plate and add to its mass.

The Editors of Encyclopaedia Britannica This article was most recently revised and updated by John P. Rafferty.