Extraterrestrial amino acids in Cretaceous/Tertiary boundary sediments at Stevns Klint, Denmark

Abstract

Since the discovery nearly a decade ago that Cretaceous/Tertiary (K/T) boundary layers are greatly enriched in iridium, a rare element in the Earth's crust, there has been intense controversy on the relationship between this Ir anomaly and the massive extinction of organisms ranging from dinosaurs to marine plankton that characterizes the K/T boundary. Convincing evidence suggests that both the Ir spike and the extinction event were caused by the collision of a large bolide (greater than 10 km in diameter) with the Earth. Alternative explanations claim that extensive, violent volcanism can account for the Ir, and that other independent causes were responsible for the mass extinctions. We surmise that the collision of a massive extraterrestrial object with the Earth may have produced a unique organic chemical signature because certain meteorites, and probably comets, contain organic compounds which are either rare or non-existent on the Earth. In contrast, no organic compounds would be expected to be associated with volcanic processes. Here we find that K/T boundary sediments at Stevns Klint, Denmark, contain both alpha-amino-isobutyric acid [AIB,(CH3)2CNH2COOH] and racemic isovaline [ISOVAL, CH3CH2(CH3)CNH2COOH], two amino acids that are exceedingly rare on the Earth but which are major amino acids in carbonaceous chondrites. An extraterrestrial source is the most reasonable explanation for the presence of these amino acids.

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

“…The results of the present study are in contrast to those of the previous study of amino acids in the K/T boundary rocks at Stevns Klint as to finding of a-aminoisobutyric acid and isovaline of extraterrestrial in origin and the diffusion of the amino acids from the K/T boundary (Zhao and Bada, 1989). The difference in the two studies probably explained by one or more of the follow ing reasons.…”

“…The concentrations of these amino acids were at most one n mol g-1 level. If a-aminoisobutyric acid and/or isovaline were present at a few n mol 9_1 (which is the level reported for the Stevns Klint Extraterrestrial amino acids in sediments at K/T boundary A negative evidence sediments (Zhao and Bada, 1989)) in the rock samples we analyzed, they could have been de tected by the methods using the amino acid ana lyzer and the GC-MS fragmentograph.…”

“…One was an enrichment of soot and charcoal at the K/ T boundary as a result of global fires triggered by the impact (Wolbach et al, 1985(Wolbach et al, , 1988Venkatesaen and Dahi, 1989). The other was un usually high occurrence of a-aminoisobutyric acid (2-amino-2-methylpropanoic acid) and isovaline (2-amino-2-methylbutanoic acid) around the K/T boundary at Stevns Klint, Denmark (Zhao and Bada, 1989). Since the two amino acids are known to be non-proteinaceous and be relatively abundant in carbonaceous chondrites, the finding supports the hypothesis of the bolide impact.…”

Thiophenes in the Cretaceous/Tertiary boundary sediments at Kawaruppu, Hokkaido, Japan.

“…Postulates for the cause of the extinctions include a global fallout of debris and dust due to an impact of an extraterrestrial body or bolide (Alvarez et al, 1980;Smit and Hertogen, 1980) and extensive volcanism (Officer and Drake, 1983;McLean, 1985). In this connection, organic geochemical studies on the Cretaceous/Tertiary (K/T) boundary sediments have found evidence for both extraterrestrial organic compounds (Zhao and Bada, 1989) and wildfires triggered by the bolide impact (Wolbach et al, ously, organic geochemical studies of amino acids (Mita et al, 1996) and dicarboxylic acids (Mita et al, 1998) in the sediments suggested the possibility of both extraterrestrial as well as terrestrial sources of these compounds. Characteristic distributions of aliphatic hydrocarbons (Mita and Shimoyama, 1999a), and polycyclic aromatic hydrocarbons (PAHs) (Mita and Shimoyama, 1999b) in the sediments were reported in relation to the massive extinction and wildfires, respectively.…”

Characterization of n-alkanes, pristane and phytane in the Cretaceous/Tertiary boundary sediments at Kawaruppu, Hokkaido, Japan.

“…A global fallout of debris and dust due to the impact of an extraterrestrial body or bolide (Alvarez et al, 1980;Smith and Hertogen, 1980) or to extensive volcanism (Officer and Drake, 1983;McLean, 1985) is thought to be the cause of the extinction. Organic geochemical stud ies on the Cretaceous/Tertiary (KIT) boundary sediments aimed to find evidence for extraterres trial organic compounds (Zhao and Bada, 1989;Mita et al, 1996Mita et al, , 1998 and wild fires triggered by the bolide impact (Wolbach et al, 1985(Wolbach et al, , 1988Venkatesan and Dahl, 1989;Heymann et al, 1994aHeymann et al, , b, 1996.…”