AGU Planet Earth Committee Report Part II Interior and Crust

T h e Ear th ' s man t l e , core , a n d crus t com­ prise 9 9 . 9 8 % of its mass . T h e man t l e , m a k i n g u p t he bulk of t he mass at 70% a n d com­ posed of h i g h e r densi ty rocks (rich in m a g n e ­ sium silicates, p lus some i ron silicates), ex­ t ends an average of 1 5 2 9 0 0 km d e e p . T h e core is the cen te r of t he Ea r th , 2 9 0 0 6 3 7 0 km d e e p , c o m p o s e d mainly of mo l t en i ron . T h e crus t is t he o u t e r m o s t layer of t he solid Ea r th , c o m p o s e d of lower densi ty rocks (rich in silica a n d a l u m i n u m a n d calcium silicates) 6 4 0 km thick. T h e Ear th ' s ocean a n d a t m o s p h e r e out gassed f rom the in te r io r very long ago , a n d economic minera l depos i t s also f o r m e d far back in the past . T o d a y , however , i m p o r t a n t processes still s h a p e t he Ea r th , such as the con t inuous recycling of volat i les—water a n d ca rbon d i o x i d e — t h r o u g h the in ter ior , as well as the chemical a n d mechanica l b r e a k d o w n of rocky mater ia l essential to soil on t he land a n d to sed imen t s in the ocean . W i t h o u t these processes, the b io sphe re could no t exist. Most of this base of t he solid Ea r th , essential to life, has been fu rn i shed on t ime scales of mil­ lions of years, m u c h longer t h a n those of cir­ culat ion a n d renewal in the ocean , a t m o ­ s p h e r e , and b iosphe re . But , by t he s ame to­ ken, those pa r t s of the e n v i r o n m e n t tha t d e p e n d on solid Ea r th processes , such as soil a n d p e t r o l e u m , canno t be r ep l en i shed in hu­ m a n t ime if exploi ted o r des t royed . A n d the solid Ea r th can also have drast ic impacts on h u m a n beings in a very shor t t ime, such as t h r o u g h e a r t h q u a k e s a n d volcanic e r u p t i o n s . U n d e r s t a n d i n g this complex system requ i r e s go ing very d e e p in to t he Ea r th a n d very far back in t ime.