674 



ARRHENIUS 



[chap. 25 



nickel iron in the form of droplets, formed by ablation of iron meteorites 

 during their passage through the atmosphere (Fig. 10b). The total amount of 

 such spherules has been estimated at a few thousand tons per year over the 

 surface of the earth (Pettersson and Fredi'iksson, 1958), which is only a fraction 

 of a per cent of the total accretion rate of cosmic matter estimated from satellite 

 measurements of micrometeorite impacts (LaGow and Alexander, 1960). 

 Associated with the partly oxidized metal spherules are chondrules (Fig. 10a) 

 consisting of olivine and pyroxene, ^ which are crystalline and thus could hardly 



Spherules per kg of carbonate-free sediment 

 1000 2000 3000 4000 5000 



Fig. 11. Frequency of cosmic iron spherules as a function of depth in core 90, Swed. 

 Deep-Sea Exped., from the West Pacific. (After Pettersson and Fredriksson, 1958.) 

 Paleontological investigations by Bramlette and Riedel (quoted by Olavisson, 1961) 

 indicate an unconformity between Quaternary and Lower Miocene at about 56 cm 

 depth. 



have formed from molten drops in the atmosphere; these are probably original 

 cosmic particles or fragments of chondritic meteorites breaking apart at entry 

 into the atmosphere. Studies of the cosmic components of pelagic sediments were 

 originally carried out by Murray and Renard {op. cit.). Recent extensive 

 investigations by Hans Pettersson have focused on the variation in time of the 

 accretion of cosmic material. The results of Pettersson and his co-workers 

 (Pettersson and Fredriksson, 1958; Fredriksson, 1958; Castaing and Fred- 

 riksson, 1958; Laevastu and Melhs, 1955; Pettersson, 1959a; Fredriksson, 1959) 

 indicate marked, world-wide changes in the rate of accretion of metallic 

 spherules during Cenozoic times (Fig. 11). Hunter and Parkin (1960) have also 



1 The presence of this latter mineral is not evident from the work of Hunter and Parkin 

 (I960) but has been established in similar chondrules by Murray and Renard (1891) and 

 Bramlette (unpublished). 



