He to the ocean sediments

EXTRATERRESTRIAL HE IN DEEP-SEA SEDIMENTS Delivery of extraterrestrial He to the ocean sediments 

Four decades ago, He of apparent extraterrestrial origin was identified in ocean sediments. Merrihue (1964) observed He/ He ratios in marine sediments roughly 2 orders of magnitude higher than those observed in atmospheric helium and attributed it to the presence of cosmic material. 

The extraterrestrial helium signal is extremely well preserved in marine and terrestrial sedimentary archives over geological time scales. Various studies have shown that the extraterrestrial helium carried to the seafloor by IDPs can be retained for periods of at least 65 million years (Ma) against diffusive and/or diagenetic loss (Farley 1995 Farley et al. 1998). Recently, Patterson et al. (1998) identified extraterrestrial He in 480-Ma old sedimentary rocks. 

Helium contained in ocean sediments can be interpreted as a mixture of helium from two sources, extraterrestrial and terrigeneous helium (Takayanagi and Ozima 1987 Marcantonio et al. 1995). Contributions from an atmospheric helium component have been shown to be negligible (e g., Farley and Patterson 1995). Assuming that the isotopic compositions of both mixing end-members are known, one can easily calculate the amount of extraterrestrial He, using the following equation  

Farley and Patterson 1995). The envelope represents mixing with the two extreme cases of terrigeneous helium signatures analyzed to date sediments derived from old continental crast (e.g., North Atlantic ice-rafted debris with He/ He = 6xlO , Marcantonio et al. 1998) and sediments from the Amazon River fan ( He/ He = 2xl0 , Marcantonio et al. 1998). 

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