Natural gas is an important fossil fuel resource composed largely of methane. Methane is also a significant greenhouse gas and, like carbon dioxide, methane concentrations in the atmosphere have increased greatly as climate shifted from cold to warm at the end of the last Ice Age. Formolo et al. suggest how, in rocks from northern Michigan, fossil fuel methane may be connected to methane as a greenhouse gas. Many thousands of years ago, microorganisms were stimulated to produce methane deep underground through decomposition of ancient sedimentary rocks when those rocks were covered by large continental ice sheets. Formolo et al. show that this subsurface microbial activity is recorded in biodegraded oil-like compounds, as well as in the DNA of microorganisms still active deep within these rocks. As long as an ice sheet remained over Michigan, methane produced by these microorganisms remained trapped underground. Once the ice began melting, however, methane that had accumulated over thousands of years was rapidly released to the atmosphere, accelerating greenhouse gas warming of the planet. Natural gas currently recovered as a fossil fuel resource in Michigan and other locations may thus represent just a small fraction of methane produced by subsurface microorganisms, most of which long since escaped to the atmosphere and contributed to climate change.
Temperature proxy data and their significance for the understanding of pyroclastic density currents
Andrew C. Scott, Geology Department, Royal Holloway University of London, Egham, Surrey TW2O OEX, UK. Pages 143-146.
Scott et al. have shown that data from plants charred by contact with hot pyroclastic (ash) flows can be used to help in the modelling of pyroclastic densi
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Geological Society of America