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Natural Gas -  Hydrocarbon based gas, mainly composed of methane, commonly found in the pores of sedimentary rocks of marine origin.
Natural Hazards -  (1) Natural phenomena that produce negative effects on life. (2) The study of the hazards of natural phenomena.
Neap Tide -  Tide that occurs every 14 to 15 days and coincides with the first and last quarter of the moon. This tide has a small tidal range because the gravitational forces of the moon and Sun are perpendicular to each other. Contrasts with spring tide.
Needle Ice -  A form of periglacial ground ice that consists of groups ice slivers at or immediately below the ground surface. Needle ice is about a few centimeters long.
Neutral -  Any substance with a pH around 7.
Neutral Atmosphere -  Condition in the atmosphere where isolated air parcels do not have a tendency to rise or sink. The parcels of air tend to be same temperature as the air that surrounds them.
Névé -  Partially melted and compacted snow that has a density of at least 500 kilograms per cubic meter.
Niche -  Describes the total range of environmental conditions that are suitable for a species existence without the effects of inter-specific competition and predation from other species.
Niche -  Adaptive role that a species has in a habitat. This includes its behavior and interactions with other species.
Nimbostratus Clouds -  Dark, gray low altitude cloud that produces continuous precipitation in the form of rain or snow. Found in an altitude range from the surface to 3,000 meters.
Nivation -  Process where snow patches initiate erosion through physical weathering, meltwater flow, and gelifluction.
Nivation Hollow -  Ground depression found in periglacial areas that is created by nivation.
Noctilucent Clouds -  High altitude clouds composed of ice crystals that appear to glow silver or bright blue shortly after sunset.
Non-Clastic Sedimentary Rock -  Sedimentary rocks that are created either from chemical precipitation and crystallization, or by the lithification once living organic matter.
Non-Renewable Resource -  Resource that is finite in quantity and is being used faster than its ability to regenerate itself.
Normal Distribution -  A common probability distribution displayed by population data. If the values of the distribution are plotted on a graph's horizontal axis and their frequency on the vertical axis the pattern displayed is symmetric and bell-shaped. The central value or mean represents the peak or the most frequently occurring value.
Normal Fault -  Vertical fault where one slab of the rock is displaced up and the other slab down. It is created by tensional forces acting in opposite directions.
Normal Lapse Rate -  Average rate of air temperature change with altitude in the troposphere. This value is approximately a decrease of 6.5° Celsius per 1000 meters rise in elevation.
North Magnetic Pole -  Location in the Northern Hemisphere where the lines of force from Earth's magnetic field are vertical. This point on the Earth gradual changes its position with time.
North Pole -  Surface location defined by the intersection of the polar axis with Earth's surface in the Northern Hemisphere. This location has a latitude of 90° North.
Nuclear Energy -  Energy released when the nucleus of an atom experiences a nuclear reaction like the spontaneous emission of radioactivity, nuclear fission, or nuclear fusion.
Nuclear Fission -  Process where the mass of an atomic nucleus is made smaller by the removal of subatomic particles. This process releases atomic energy in the form of heat and electromagnetic radiation.
Nuclear Fusion -  Process where the mass of an atomic nucleus is made larger by the addition of subatomic particles. This process releases atomic energy in the form of heat and electromagnetic radiation.
Nuee Ardente -  A glowing cloud of dense hot volcanic gas and ash that moves downslope at high speeds, incinerating the landscape.
Null Hypothesis -  Is a hypothesis that has been suggested because it is believed to be true or because it is to be used as a starting point for scientific argument. Used in statistical testing to organize arguments.
Nutrient -  Any food, chemical element or compound an organism requires to live, grow, or reproduce.
Nutrient Cycle -  The cycling of a single element by various abiotic and biotic processes through the various stores found in the biosphere, lithosphere, hydrosphere, and atmosphere.