Structure of the Earth obducted onto the continental crust and preserved as ophiolite sequences. Many rocks now making up Earth's crust formed less than 100 million (1) years ago; however, the oldest known mineral grains are about 4.4 billion (4.4) years old, indicating that Earth has had a solid crust for at least 4.4 billion years. Earth's mantle extends to a depth of 2,890 km, making it the thickest layer of Earth. The mantle is divided into upper and lower mantle. The upper and lower mantle are separated by the transition zone. The lowest part of the mantle next to the core-mantle boundary is
Civilization and Its Discontents Civilization and Its Discontents Civilization and Its Discontents is a book by Sigmund Freud, the founder of psychoanalysis. It was written in 1929 and first published in German in 1930 as "Das Unbehagen in der Kultur" ("The Uneasiness in Civilization"). Exploring what Freud sees as the important clash between the desire for individuality and the expectations of society, the book is considered one of Freud's most important and widely read works, and one of the most influential and studied books in the field of modern psychology. Freud enumerates what he sees as the fundamental tensions between civilization and the individual.