It may not look it, but all tless drag of gravity. Remove a pane of really old glassfrom t iceably t ttom t top. t is t of “floalking about. t ten times faster tle.

    ts occur not just laterally as tes move across t upand doion.

    Convection as a process  deduced by tric Count von Rumford at teentury. Sixty years later an Englislysuggested t terior migents to move about,but t idea took a very long time to gain support.

    In about 1970,  urmoil  came as a considerable s it in t ists  decades figuring out tmospropospratosp about wind.”

    ion process goes ter of controversy ever since. Somesay it begins four refil  “ts of data, from t disciplines,t cannot be reconciled.” Geocs say t certain elements on Eartle, but must h.

    terials in tle must at least occasionally mix.

    Seismologists insist t to support suchesis.

    So all t can be said is t at some sligerminate point as er of Earto pure mantle. Considering t itaccounts for 82 percent of t of its mass, tle doesn’tattract a great deal of attention, largely because t interest Eartists andgeneral readers alike ism) or nearer t to a dept a le consistspredominantly of a type of rock knoite, but ain. According to a Nature report, it seems not to be peridotite. More t know.

    Beneatle are ter one. Needless tosay, our understanding of ture of t, but scientists can make somereasonable assumptions. t t ter of tly imes t to turn anyrock tory (among ot t retaining its . Alt is little more t is t t in