Sea level decrease: changes the pressure and destabilizes the methane gas, which then bubbles up to the surface and causes problems in the atmosphere All sentiments on top of the zone of gas-hydrates slump down causing a landslide o Sea-level increases: dangerous in arctic climates where gas hydrate ice forms in bands and lenses close to the surface The rise in sea-level causes relatively warm ocean water to cover the ice resulting in a breakdown of the stable gas hydrates within the sediment, which releases methane gas into the atmosphere Coal: • Sedimentary rock that consists of carbon mixed with minor amounts of organic chemicals, quartz and clay (not a mineral) • Forms : from no other organisms but from plant remains (wood, steams, leaves (peat)) that once grew in coal swamps – regions that resembled the wetlands and rain forests of modern tropical or semitropical coastal area o Vegetation of this ancient swamp must fall and be buried in oxygen-poor environment (ex. stagnant water) so that it can be incorporated in a sedimentary sequence without reacting to oxygen or being eaten o Compaction and partial decay of this vegetation at depths of sediment of 4-10 km transforms in into peat At this depth the weight of the overlying sediment compacts the peat and squeezes out any remaining water Also, at this depth the increase in temperature gradually heats the peat accelerates chemical reactions that gradually destroy plant fiber and release elements such as hydrogen, nitrogen, and sulfur in the form of gas (i.e. get rid of unneeded gasses) leaving behind concentrated carbon Key is to burry organic material quickly to preserve it and cut off oxygen supply o Deep burial occurs: when the surface of the continent gradually sinks creating a depression or sedimentary basin that can collect sediment o Type of sediment deposited depends on sea level, as it advances it buries the plant remains very quickly • Fossil fuel : stores solar energy from photosynthesis that reached earth a long time ago o Extensive coal deposits in the carboniferous-age strata (286-354 million years ago) • Carbon : when the residue exceeds 70% carbon = coal
Emsellem 3 o Higher the concentration of carbon the better the quality, therefore the further burial and higher temperatures = more carbon = better quality coal • Peat = 50% carbon • Lignite = soft, dark-brown coal, 70% carbon • Bituminous = lignite turns into with higher temperatures, dull, black, 85% carbon • Anthracite = purest form of coal, transformed bituminous, shiny, back (hard coal), 95% carbon o Best reserves in Pennsylvania o Requires high temperatures that develop only on the borders of mountain belts, along thrust faults o Produces more energy than lignite because it has a higher carbon concentration o As carbon content of coal increases the coal rank increases • Coalbed methane: the natural process by which coal forms underground yields large quantities of methane (natural gas that is colorless and odorless) o
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- Fall '11
- Geology, Aquifer, Oil shale, methane gas