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
The Public and its Problems The Public and its Problems The Public and its Problems is a 1927 book by American philosopher John Dewey. In his first major work on political philosophy, Dewey explores the viability and creation of a genuinely democratic society in the face of the major technological and social changes of the 20th century, and seeks to better define what both the 'public' and the 'state' constitutes, how they are created, and their major weaknesses in understanding and propagating its own interests and the public good. Dewey rejects a then popular notion of political technocracy as an alternative system of governing an