Carbon dioxide, a greenhouse gas that has become a bane of modern society, may have saved Earth from freezing over early in the planet's history, according to the first detailed laboratory analysis of the world's oldest sedimentary rocks.
Scientists have theorized for years that high concentrations of greenhouse gases could have helped Earth avoid global freezing in its youth by allowing the atmosphere to retain more heat than it lost. Now a team from the University of Chicago and the University of Colorado at Boulder that analyzed ancient rocks from the eastern shore of Hudson Bay in northern Quebec, Canada, have discovered the first direct field evidence supporting this theory.
The study shows carbon dioxide in Earth's atmosphere could have sustained surface temperatures above freezing before 3.75 billion years ago according to the researchers, led by University of Chicago Assistant Professor Nicolas Dauphas. Co-authors on the study, which appeared online Jan. 16 in the journal Earth and Planetary Science Letters, included Assistant Professor Stephen Mojzsis and doctoral student Nicole Cates of CU-Boulder's geological sciences department and Vincent Busigny, now of the Institut de Physique du Globe in Paris.
The new study helps explain how Earth may have avoided becoming frozen solid early in its history, when astrophysicists believe the sun was 25 percent fainter than today. Previous studies had shown liquid water existed at Earth's surface even though the weak sun should have been unable to warm the planet above freezing conditions. But high concentrations of CO2 or methane could have warmed the planet, according to the research team.
The ancient rocks from Quebec contain iron carbonates believed to have precipitated from ancient oceans, according to the study. Since the iron carbonates could only have formed in an atmosphere containing far higher CO2 levels than those found in Earth's atmosphere today, the re
Contact: Stephen Mojzsis
University of Colorado at Boulder