Lithosphere of these xenoliths have been investigated by many methods, including analyses of abundances of isotopes of osmium and rhenium. Such studies have confirmed that mantle lithospheres below some cratons have persisted for periods in excess of 3 billion years, despite the mantle flow that accompanies plate tectonics. Lithosphere A lithosphere ( ["lithos"] for "rocky", and ["sphaira"] for "sphere") is the rigid, outermost shell of a terrestrial-type planet, or natural satellite, that is defined by its rigid mechanical properties. On Earth, it is composed of the crust and the portion of the upper mantle that behaves elastically on time scales of
What to the Slave Is the Fourth of July? under the sea, as well as on the earth. In the United States, the speech is widely taught in history and English classes in high school and college. American studies professor Andrew S. Bibby argues that because many of the editions produced for educational use are abridged, they often misrepresent Douglass's original through omission or editorial focus. The speech has been notably performed or read by important figures, including the following actors: What to the Slave Is the Fourth of July? "What to the Slave Is the Fourth of July?" is the title now given to a speech by Frederick