Search for extraterrestrial amino acids in sediments at the Cretaceous/Tertiary boundary in Kawaruppu, Hokkaido, Japan.

Abstract

Amino acids in the Cretaceous/Tertiary (K/T) boundary sediments at Kawaruppu were analyzed. A maximum of eight kinds of amino acids including diagenetically unstable serine and threonine was detected in the water extracts at most at one n mol g–1 sample level. The number of kinds and quantities of amino acids from the HCl extracts were smaller than those from the water extracts. The D/L ratios of these amino acids indicate that they are not so old as 65 million years. α-Aminoisobutyric acid (2-amino-2-methylpopanoic acid) and isovaline (2-amino-2-methylbutanoic acid) were not detected in any samples, in contrast to the previous study of amino acids in the K/T boundary at Stevns Klint, Denmark (Zhao and Bada, 1989). Our results show that amino acids of possible extraterrestrial and/or 65 million year old terrestrial in origin were not present in the K/T boundary at Kawaruppu. Three plausible explanations for the different results between the present and previous studies are discussed in the text. In addition, our results do not support the cometary dust origin proposed for the presence of the two extraterrestrial amino acids at Stevns Klint (Zahnle and Grinspoon, 1990).