Australia: The Land Where Time Began

A biography of the Australian continent 

Atmospheric Carbon Dioxide - A 300-Million-Year record from Plant Cuticles

According to the author¹ geochemical proxies are used to reconstruct past atmospheric CO₂ levels in order to better understand the link between atmospheric CO₂ and climate over geological time (Berner, 1997; Pearson & Palmer, 2000; Ekart et al., 1999; Pagani, Freeman & Arthur, 1999). A broad picture of the variation of atmospheric CO₂ throughout the Phanerozoic, that covers the last 544 My, has been provided by these records, though there are still some inconsistencies and gaps requiring attention. In this article the author¹ presents evidence, based on stomatal abundance in fossil leaves from 4 plant genera closely related to the Ginkgo of the present, for a continuous record spanning 300 My. He reconstructed atmospheric CO₂ concentrations based on the known relationship between the number of stomata on a leaf and CO₂ concentrations in the growing season. The record he constructed indicated that over the last 300 My there were 2 episodes in which there were intervals when the atmospheric CO₂ concentrations were low, less than 1,000 ppmv, and both of these intervals coincided with known ice ages occurring in the Neogene  8-1 Ma and Early Permian, 290-275 Ma. The levels of atmospheric CO₂ were high, 1,000-2,000 ppmv, 250-65 Ma, most of the Mesozoic, though in this period there were intervals during which there were excursions in the atmospheric CO₂ levels above 2,000 ppmv. The results of the author's study are consistent with some past CO₂ record reconstructions (Berner, 1997; Pearson & Palmer, 2000), and palaeotemperature records (Veizer, Godderis & François, 2000), though they suggest the reconstructions based on carbon isotope proxies (Ekart et al., 1999; Pagani, Freeman & Arthur, 1999) may be compromised by isotopically light methane that was released as episodic outbursts (MacLeod & Wing, Krull et al., 2000). According to the author¹ water vapour, CO₂ and methane were involved in greenhouse climate warming over the last 300 My.

Sources & Further reading

1. Retallack, G. J. "A 300-Million-Year Record of Atmospheric Carbon Dioxide from Fossil Plant Cuticles." Nature 411 (// 2001): 287-90.