High-precision age for the Haifanggou Formation and its implications for the coevolution of plants and atmospheric CO2

Abstract

Atmospheric CO2 levels have fluctuated greatly during the Phanerozoic [1]. Although many organic and inorganic factors affected atmospheric CO2 levels, plants have played an important role in CO2 fluctuations. Recently, most paleobotanists accept an Early Cretaceous origin for angiosperms and support that angiosperms underwent a rapid ecological radiation in middle-late Cretaceous [2]. Because high concentrations of Cretaceous atmospheric CO2 underwent a long-term decline, several hypotheses suggested that the origin and radiation of angiosperms and atmospheric CO2 levels are closely related [3]. The recent discovery of Schmeissneria from the middle part of the Jurassic Haifanggou Formation provided evidence that the origin of angiosperms could predate the Early Cretaceous [4]. Because previously reported ages for the Haifanggou Formation are scattered and the uncertainties of these ages were fairly large, our on-going work aims to establish high-precision 40Ar/39Ar ages for volcanic ashes from the Haifanggou Formation. Our preliminary results indicate that Schmeissneria is older than 160 Ma. The age results will provide a robust geochronological calibration for the oldest angiosperm and will improve our knowledge of the link between atmospheric CO2 and the rise and the radiation of angiosperms. [1] Berner et al. (2001) American Journal of Science 301, 182-204. [2] Friis et al. (2005) Current Opinion in Plant Biology 8, 5-12. [3] Beerling (1994) Philosophical Transactions of the Royal Society, London B346, 421-432. [4] Wang et al. (2006) Progress in Natural Science 16, 222-230.