Debate about the earth

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BOOK REVIEWS

Debate about the Earth (revised edition). H. TAKEUCHI, S. UYEDA, AND H . KANAMORI. Freeman-Cooper, San Francisco, 1970. 281 pp. Price $5.25 H a r d b o u n d ; $2.80 P a p e r b o u n d . The explosive d e v e l o p m e n t of E a r t h science in t h e p a s t five y e a r s has n e c e s s i t a t e d t h e addition o f a new c h a p t e r , on ocean-floor s p r e a d i n g a n d p l a t e tectonics, to t h e revised edition of this d e s e r v e d l y p o p u l a r book. The result is a concise a n d compelling a c c o u n t of t h e rise a n d fall a n d s u b s e q u e n t r e s u r r e c t i o n o f t h e t h e o r y o f cont i n e n t a l drift. Much of t h e book was w r i t t e n in t h e early 1960's, w h e n c o n t i n e n t a l drift was highly controversial a n d its p r o p o n e n t s s o m e t i m e s e v a n gelical in t h e i r fervor. The a u t h o r s h a v e been v e r y successful in c o n v e y i n g t h e e x c i t e m e n t o f this p e r i o d while m a i n t a i n i n g strict i m p a r t i a l i t y in t h e i r t r e a t m e n t of t h e e v i d e n c e for a n d a g a i n s t c o n t i n e n t a l drift. This h a p p y blend o f flavor' a n d f a c t owes m u c h t o t h e easy, c o n v e r s a t i o n a l s t y l e o f t h e book a n d to t h e skilful use o f t h e c o n t i n u i n g d e b a t e over c o n t i n e n t a l drift, fi'om 1910 to t h e present., as a u n i f y i n g t h e m e c o n n e c t i n g t h e diverse g e o p h y s i c a l topics t r e a t e d . O f t e n t h e s e s u b j e c t s are c o v e r e d in a d e p t h a n d detail w h i c h m i g h t seem out. of p r o p o r t i o n to t h e i r relevance to global t e c t o n i c theories, b u t t h e p r e s e n t a t i o n s are u n i f o r m l y so e n t e r t a i n i n g t h a t t h e y n e v e r a p p e a r to i n t r u d e u p o n t h e b o o k ' s t h e m e . N e v e r t h e l e s s , some of t h e discussions, of geom a g n e t i s m a n d rock m a g n e t i s m in C h a p t e r s 3 a n d 4, of t h e E a r t h ' s t h e r m a l h i s t o r y in C h a p t e r 6, a n d of sea-floor s p r e a d i n g in C h a p t e r 8 in p a r t i c u l a r , could well s t a n d as i n d e p e n d e n t treatises a n d are far superior to t h e discussions given in m o s t t e x t books on geophysics. The book begins, v e r y properly, w i t h a succinct s t a t e m e n t of Alfred V~'egener's basic c o n t e n t i o n : "Once, t h e r e was no A t l a n t i c . " T h e t w o introd u c t o r y c h a p t e r s are w r i t t e n w i t h t h e color a n d i m m e d i a c y of a good n e w s p a p e r story. T h e y trace t h e d e v e l o p m e n t of ~hregener's ideas into a global t h e o r y of t e c t o n i c s a n d s u m m a r i z e t h e o f t e n b i t t e r c o n t r o v e r s y w h i c h ensued. Was t h e occurrence of s o m e similar p l a n t a n d animal species in widely s e p a r a t e d c o n t i n e n t s a result of drift or of n o w - s u b m e r g e d l a n d bridges': Were geological a n d g e o m e t r i c a l similarities b e t w e e n t h e A t l a n t i c coasts of N o r t h A m e r i c a a n d E u r o p e a n d of S o u t h A m e r i c a a n d Africa real or m e r e l y wishfid t h i n k i n g on t h e p a r t of ~Vegener a n d his s u p p o r t e r s ? Could coal a n d desert s a n d s t o n e s in polar regions, r o u g h l y c o n t e m p o r a n e o u s w i t h glaciers n e a r t h e p r e s e n t day e q u a t o r , be e x p l a i n e d by global climatic

c h a n g e s or was it necessary to i n v o k e drift? The q u e s t i o n (still a s t u m b l i n g block t o d a y ) of t h e d r i v i n g m e c h a n i s m of t h e p r o p o s e d global scale m o v e m e n t s is given p r o m i n e n t coverage, beginning in t h e s e c o n d c h a p t e r w i t h E6tvos" pole-fleeing force a n d p r o c e e d i n g e v e n t u a l l y to H o l m e s ' suggestion of a c o n v e y o r belt driven b y c o n v e c t i o n in a " s o l i d " m a n t l e . E v i d e n c e b e a r i n g on m a n t l e c o n v e c t i o n is e x a m i n e d in C h a p t e r s 6 a n d 7. F o r t h e m o s t p a r t , t h e e v i d e n c e is indirect a n d b a s e d on u n e x p e c t e d l y high average h e a t flow in t h e o c e a n basins. T h e a u t h o r s (p. 197) do n o t m a k e clear, however, w h y conv e c t i v e h e a t t r a n s f e r in t h e m a n t l e is f a v o r e d over r a d i a t i v e transfer. C o n t i n e n t a l d r i f t was n e v e r decisively p r o v e n or d i s p r o v e n in W e g e n e r ' s own time. I n d e e d . t h e v e r y inconclusiveness of t h e e v i d e n c e led to its decline to t h e e v e n t u a l s t a t u s of a d e a d t h e o r y . C h a p t e r 5 deals w i t h a b r u p t revival of i n t e r e s t in (and c o n t r o v e r s y over) c o n t i n e n t a l drift w i t h t h e a d v e n t of p a l e o m a g n e t i s m . The early d e v e l o p m e n t of p a l e o m a g n e t i s m is pres e n t e d as a l m o s t a duel b e t w e e n t w o rival B r i t i s h laboratories, L o n d o n a n d N e w c a s t l e . D e s p i t e t h e i m p r e s s i o n given b y m o s t books a b o u t science a n d scientists, personalities h a v e always p l a y e d a large p a r t in t h e d e v e l o p m e n t of new ideas, n o w h e r e more so t h a n in paleon m g n e t i s m . The a u t h o r s ' a p p r o a c h is t h e r e f o r e a novel a n d refreshing one, c a p t u r i n g a d m i r a b l y t h e d r a m a of t h e parallel d e v e l o p m e n t of t h e c o n t i n e n t a l drift a n d polar w a n d e r h y p o t h e s e s . Still, t h e a u t h o r s , in e m p h a s i z i n g t h e d r a m a t i c initial i m p a c t of p a l e o m a g n e t i s m , h a v e p e r h a p s gone too far. The r e a d e r is left w o n d e r i n g if' p a l e o m a g n e t i s m has simply s t a g n a t e d since the early work of B l a c k e t t a n d R u n e o r n . I n d e e d . he m a y well be u n c e r t a i n w h e t h e r a n y work in t h e s u b j e c t has ever b e e n c o n d u c t e d outside E n g l a n d . Only passing m e n t i o n is m a d e of t h e excellent w o r k in t h e m l t h o r s ' o w n c o u n t r y , while t h e p i o n e e r i n g w o r k of I r v i n g in Australia a n d Cox a n d Doell in t h e U.S. is n o t m e n t i o n e d at all. C h a p t e r 6 t r e a t s t h e t h e r m a l h i s t o r y of t h e E a r t h , w i t h p a r t i c u l a r reference to h e a t flow a t t h e surface a n d t h e possibility of a growing core. w h i c h could c o n c e i v a b l y cause a b r u p t c h a n g e s in m a n t l e c o n v e c t i o n p a t t e r n s a n d initiate periods of orogenesis. I n view of t h e fairly e x t e n s i v e c o n s i d e r a t i o n of t h e f o r m a t i o n o f t h e solar s y s t e m , a brief c o n s i d e r a t i o n of t h e t h e r m a l a n d possible t e c t o n i c h i s t o r y o f such i n t e r e s t i n g p l a n e t s a n d satellites as Venus, Mars, a n d t h e Moon would have, been welcome, b u t t h e author's e v i d e n t l y considered this too g r e a t a digression. Chapters 7 and 8 treat the tectonic evidence

BOOK REVIEWS r e c o r d e d i n t h e o c e a n basins, c u l m i n a t i n g in t h e c a l c u l a t i o n of r a t e s of sea-floor s p r e a d i n g b y comparing linear positive and negative magnetic a n o m a l i e s parallel to m i d - o c e a n i c ridges w i t h t h e g e o m a g n e t i c p o l a r i t y t i m e scale. C h a p t e r 7 describes t h e global p a t t e r n of oceanic ridges, faults, a n d t r e n c h e s , t o g e t h e r w i t h t h e i r interp r e t a t i o n f r o m t h e p a r t i c u l a r v i e w p o i n t of cont i n e n t a l drift. T h e c o n f i r m a t i o n of t h e essential a s p e c t s of t h i s i n t e r p r e t a t i o n since t h e mid1960's is r e v i e w e d in C h a p t e r 8. T h e d i s c o v e r y t h a t t h e s e q u e n c e of p o s i t i v e a n d n e g a t i v e a n o m alies a b o u t m i d - o c e a n ridges a c c u r a t e l y m i r r o r s epochs of p o s i t i v e a n d n e g a t i v e p o l a r i t y of t h e E a r t h ' s m a g n e t i c field a n d t h e d e m o n s t r a t i o n t h a t oceanic f a u l t s are t r a n s f o r m a n d n o t t r a n s c m ' r e n t f a u l t s m a k e s t h e basic n o t i o n of sea-floor s p r e a d i n g a l m o s t i n c o n t e s t a b l e . Yet, as t h e a u t h o r s are careful to p o i n t out, t h e e n t i r e p i c t u r e is n o t clear. I t is difficult to e x p l a i n offsets i n t h e m i d - o c e a n i c ridges, for e x a m p l e , if c o n v e c t i o n c u r r e n t s are t h e sole d r i v i n g m e c h anism. The authors might have pointed out that triple j u n c t i o n s of t h r e e m i d - o c e a n ridges, s u c h as t h o s e in t h e G u l f of A l a s k a a n d s o u t h of t h e R e d Sea, are equally puzzling. Well o v e r 100 d i a g r a m s i l l u s t r a t e t h e book. T h e s e are u n u s u a l l y well done, h a v i n g b e e n r e d r a w n in a s t a n d a r d style a n d n o t s i m p l y r e p r o d u c e d f r o m t h e i r original sources, a n d a d d a g r e a t deal t o t h e a p p e a r a n c e a n d r e a d a b i l i t y of t h e v o l u m e . T h e p h o t o g r a p h s of l e a d i n g figures in t h e field are less successful a n d Figs. 3-20 a n d 3-21 are of such p o o r q u a l i t y t h a t t h e y might, b e t t e r h a v e b e e n d i s p e n s e d with. T h o s e of ~ ; e g e n e r , B l a c k e t t , a n d N~el, h o w e v e r , are v e r y clear. " D e b a t e a b o u t t h e E a r t h " is a h i g h l y e n t e r r a i n i n g book, t r e a t i n g t h e s u b j e c t of c o n t i n e n t a l d r i f t w i t h clarity, coinpleteness, a n d a c c u r a c y . I t is e q u a l l y good as a q u i c k p r i m e r in basic m o d e r n ideas a b o u t t h e physics of t h e E a r t h . W h e t h e r t h e r e a d e r be scientist, s t u d e n t or l a y m a n , t h i s b o o k h a s m u c h to offer. DAVID J . DUNLOP

Erindale College I ~niversity of Toronto Clarkson, Ontario, Canada Planetary Atmospheres (International Astronomical Union Symposium No. 40). E d i t e d b y CARL SAG'AN, TOBIAS C. O~VEN, AND HARLAN J . S.~HTm D. Reidel, H o l l a n d , a n d S p r i n g e r - V e r l a g , N e w Y o r k , 1971. xvii + 408 pp. $25.00. T h i s is a collection of t h e p a p e r s p r e s e n t e d a t [ A U S y m p o s i u m ~ o . 40, held a t Marfa, Texas,

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O c t o b e r 26-31, 1969. T h e r e are 53 p a p e r s in all, c o v e r i n g p r a c t i c a l l y e v e r y a s p e c t of t h e s u b j e c t of p l a n e t a r y a t m o s p h e r e s . Some, h u t n o t m u c h , of t h e discussion following i n d i v i d u a l p a p e r s is recovered. T h e b o o k is o r g a n i z e d i n t o t h r e e p a r t s : Venus, Mars, a n d O u t e r P l a n e t s . T h e Mars section is t h e largest, a m o u n t i n g to h a l f t h e book. A list of t h e s u b h e a d i n g s for t h i s section shows t h e v a r i e t y of topics r e p r e s e n t e d : optical p r o p e r t i e s , CO2 a b s o r p t i o n , w a t e r v a p o r a b s o r p tion, M a r i n e r results, cloud m o t i o n s a n d atmospheric dynamics, upper atmospheres. A few of t h e p a p e r s in t h e v o l u m e are o n l y a b s t r a c t s a n d a few o t h e r s are s u m m a r i e s or r e p r i n t s of articles w h i c h h a v e a p p e a r e d elsewhere. Most, h o w e v e r , are original. I shall n o t t r y to discuss i n d i v i d u a l p a p e r s in detail, b u t let m e m e n t i o n a few w h i c h especially i n t e r e s t e d me. A p a p e r b y V i n o g r a d o v , S u r k o v , Andreichikov, Kalinkina, and Grechischeva, " T h e c h e m i c a l c o m p o s i t i o n of t h e a t m o s p h e r e of V e n u s , " describes t h e c h e m i c a l c o m p o s i t i o n sensors c a r r i e d b y V e n e r a -4, -5, a n d -6 in m o r e d e t a i l t h a n I h a v e seen elsewhere. T h e r e is a n i n t e r e s t i n g a n d r e a d a b l e review b y S a g a n entitled "The trouble with Venus." I enjoyed a review b y Schorn, " T h e spectroscopic s e a r c h for w a t e r o n Mars : a h i s t o r y . " A p a p e r b y Ingersoll, " M a r s : o c c u r r e n c e of liquid w a t e r , " discusses t h e severe c o n s t r a i n t s u p o n t h e occm.rence of liquid w a t e r o n Mars d u e to low t e m p e r a t u r e s a n d h i g h e v a p o r a t i o n rate. P a p e r s b y Boyce, de Vaueoulers, a n d B a u m a n d M a r t i n discuss v a r i o u s aspects of cloud o c c u r r e n c e a n d m o v e m e n t on M a r s ; i n f o r m a t i o n w h i c h is t a n t a l i z i n g a n d will some d a y be useful to d y n a m i c i s t s , once we k n o w t h e n a t u r e a n d a l t i t u d e of t h e clouds a n d h a v e a b e t t e r t h e o r e t i c a l basis for i n t e r p r e t a t i o n . T h e v o l u m e also c o n t a i n s ( r e p r i n t e d f r o m Science) " M a r i n e r 6 a n d 7 television p i c t u r e s : p r e l i m i n a r y a n a l y s i s , " b y L e i g h t o n et al. T h e r e is a p a p e r b y Coffeen, " V e n u s cloud c o n t r a s t s , " in which observations on the wavelength depend e n c e of c o n t r a s t s are p r e s e n t e d , t o g e t h e r w i t h some c o m m e n t s o n t h e difficulty of i n t e r p r e t a t i o n of t h i s d a t a . I n t h e O u t e r P l a n e t s section, S t r e e t t h a s a p a p e r , " P h a s e b e h a v i o r of l i g h t gas m i x t u r e s a t h i g h p r e s s u r e s , " in w h i c h he suggests t h a t t h e s t r u c t u r e of t h e g i a n t p l a n e t s m a y be c o m p l i c a t e d b y little u n d e r s t o o d H 2 - H e m i x t u r e p h a s e changes. A m o n g t h e o t h e r a u t h o r s r e p r e s e n t e d are: Golitsyn, W e s t p h a l , Teifel, T r a f t o n a u d W i l d e y , D a l g a r n o a n d Deggs, K u i p e r , C r u i k s h a n k , B a r k e r , Sill, F i n k , v a n de H u l s t , K a p l a n , a n d Young. T h e book is a n i n t e r e s t i n g a n d v a l u a b l e collection of papers. A n y o n e i n t e r e s t e d e n o u g h