Abstract
AbstractReactions involving carbon in the deep Earth have limited manifestations on Earth's surface, yet they have played a critical role in the evolution of our planet. The metal-silicate partitioning reaction promoted carbon capture during Earth's accretion and may have sequestered substantial carbon in Earth's core. The freezing reaction involving iron-carbon liquid could have contributed to the growth of Earth's inner core and the geodynamo. The redox melting/freezing reaction largely controls the movement of carbon in the modern mantle, and reactions between carbonates and silicates in the deep mantle also promote carbon mobility. The 10-year activity of the Deep Carbon Observatory has made important contributions to our knowledge of how these reactions are involved in the cycling of carbon throughout our planet, both past and present, and has helped to identify gaps in our understanding that motivate and give direction to future studies.
Highlights
Most people know there is carbon in the atmosphere, mainly due to the rising threat of climate change, not all are aware that the amount of carbon in the atmosphere is around one hundred thousand times less than that stored in other surface reservoirs (Falkowski et al 2000) and that the amount of carbon in Earth’s interior is thought to be at least three million times greater than the amount in the atmosphere (Dasgupta and Hirschmann 2010)
How are deep Earth reactions important to the past and future evolution of our planet? This paper provides a snapshot of perspectives from those attending the “Earth in Five Reactions” workshop through a survey of deep Earth carbon reactions, focusing on what we know and do not know, and especially what we would like to know
Until 2015, most models considered decarbonation reactions and melting as the dominant processes mobilizing carbon from subducting slabs, and predicted that about half of subducted carbon is recycled into the deep mantle (e.g., Dasgupta and Hirschmann 2010)
Summary
Most people know there is carbon in the atmosphere, mainly due to the rising threat of climate change, not all are aware that the amount of carbon in the atmosphere is around one hundred thousand times less than that stored in other surface reservoirs (e.g., the oceans and continents) (Falkowski et al 2000) and that the amount of carbon in Earth’s interior (mantle and core) is thought to be at least three million times greater than the amount in the atmosphere (Dasgupta and Hirschmann 2010). They can contain several tens of weight percent of carbon dioxide that can remain dissolved in the melt until very low pressure (e.g., Moussallam et al 2015) These melts are considered to evolve during ascent, becoming progressively silica-rich as they react with the mantle (e.g., Dasgupta and Hirschmann 2010), yet they might stall and pond, potentially accumulating at the lithosphere-asthenosphere boundary and explaining the so-called low velocity zone (e.g., Sakamaki et al 2013). It still remains to be determined if diamonds reflect ubiquitous precipitation from methane- and carbon dioxide-bearing water-rich fluids (e.g., Smit et al 2016), or if diamonds are formed exclusively by carbonate-bearing and methane-free oxidized fluids or melts, or something else altogether
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