The Bulag Hypothesis

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Studying the global carbon cycle, or the exchange of carbon among the Earth’s atmosphere, lithosphere, hydrosphere, and biosphere, is important to understanding the Earth’s climate changes. One explanation for the long-term carbon cycle is offered by the BLAG spreading rate hypothesis, developed by Berner, Lasaga, and Garrels in 1983 to link plate tectonics to the changes in the atmospheric carbon dioxide concentration and global climate. The intent of this paper is to discuss the central ideas of the BLAG hypothesis and the evidence supporting or opposing these ideas. The BLAG hypothesis suggests that global climate changes in the past 100 million years are driven by the long-term carbon dioxide concentration changes in the atmosphere …show more content…

According to the available data and calculations, the global mean rate of seafloor spreading was faster 100 million years ago than in the present. Moreover, the absence of large polar ice sheets in this time period indicates that the global climate was warmer than it is today. Such correlation between the seafloor spreading rate and global climate seems to support the BLAG hypothesis, which suggests that the rate of the carbon dioxide input to the atmosphere was higher 100 million years ago than in the present. The BLAG hypothesis may also explain the global cooling period between 55 and 15 million years ago, when there was a general decrease in the seafloor spreading rate. However, geologic evidence shows that the greater global cooling occurred between 55 million years ago and the present, which is not consistent with the BLAG hypothesis (Raymo and Ruddiman, 1992). The historical records of the ocean chemistry, specifically of the varying calcium and magnesium concentrations, also do not have an observable association with the seafloor spreading rate as expected from the BLAG hypothesis (Kump, 2008). Furthermore, the increased chemical weathering in the past 40 million years of global cooling seems to contradict the idea of chemical weathering being a negative feedback mechanism to regulate climate changes (Raymo and Ruddiman,

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