Magnetic Spherules — Pettersson and Frederiksson 
81 
The number of such spherules obtained by 
means of a powerful electromagnetic extractor 
is tens of times greater than the numbers 
found by Sir John Murray and A. F. Renard 
by more primitive means. 
Spherules in considerable numbers are 
found also in depths of several metres below 
the sediment surface, i.e., in sediments al- 
ready deposited in Tertiary Time. This defi- 
nitely refutes the hypothesis that meteoritic 
falls, from which the spherules are assumed 
to be derived, have been limited to a relatively 
recent past, the last 25,000 years. 
On the other hand there are strong indica- 
tions that the frequency of such spherules 
deposited in recent times, say in the last few 
thousand years, has been higher than in a 
more remote past. 
There are also indications of intermediate 
maxima which may correspond to a greater 
frequency of meteoritic falls during certain 
times covered by our material. A systematic 
correlation of such maxima inter se has not 
been made. 
Comparing the frequency of spherules 
found in recent times, i.e., near the surface, 
in certain cores affords means of estimating 
the approximate rates of sedimentation. 
Converting the number of spherules found 
per kg. of sediment into weights makes it 
possible to estimate the total accruement of 
spherules to the whole Earth, the results being 
a moderate figure of 2,400 metric tons an- 
nually (with a possible rise to 5,000 tons), 
i.e., only a small fraction of figures obtained 
by earlier investigators from the number of 
magnetic spherules collected from the atmos- 
phere. Means of obtaining more reliable fig- 
ures for such spherules by establishing collec- 
tion stations on mid-ocean islands are in- 
dicated. 
In cases where the number of spherules 
from deep-sea cores have been analysed for 
iron, nickel, and cobalt, the presence of 
nickel has given a definite proof of the cosmic 
origin of the deep-sea spherules. 
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