Ancient Oxygen Levels of Paleozoic Fluid Inclusions
Abstract
The Paleozoic (500-300 million years) was a dynamic era in Earth’s history characterized by environmental diversity and multiple extinction events. Understanding climate change throughout the Paleozoic not only allows for paleoclimate reconstruction but offers a glimpse into how life has progressed through time. By studying oxygen, one of the most important facets of any climate, the fluctuation of oxygen and its link to rises and declines of life throughout the Paleozoic may be studied. Halite offers a unique approach to studying the facets of Earth’s past temperatures due to its ability to form fluid inclusions, which can be studied using microthermometry to measure actual formation temperatures during halite crystallization at the brine-surface interface. This study aims to utilize halite-hosted fluid inclusions that contain trapped air bubbles to determine the atmospheric concentration of oxygen and Paleozoic temperatures at which the halite precipitated, as well as chemical characteristics in each area that the halite precipitated. This study utilizes multiple methodologies, including cutting-edge gas analysis to directly measure the atmospheric gases trapped in fluid inclusions, microthermometry and trace chemistry.
Using halite dated to the Cambrian, Silurian and Permian from various areas, respectively Australia, Canada and the United States allows for a detailed understanding of their environmental conditions during halite crystallization, by determining surface atmospheric air composition, temperature at halite formation and trace chemical characteristics of the halite and surrounding strata. Atmospheric oxygen concentrations ranged throughout the Paleozoic and changed when approaching or following extinction events. In the late Cambrian, O2 levels were around 11.60% (± 1.04). In the Silurian, an environmentally stable period, O2 increased to 16.23% (± 1.04), closer to modern atmospheric levels of ~ 21%. The Permian, a period of extinction events, saw the beginning of a decrease in O2 content, from 16.05% (± 1.04) in the Leonardian stage (280 Ma), before dropping to 10.08% (± 1.04) O2 in the Guadalupian stage (260 Ma) as the end-Guadalupian extinction occurred. These results provide insight on the fluctuations of both surface temperatures and atmospheric oxygen levels.