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natural gas

A hydrocarbon gas mixture composed primarily of methane (CH4), but also small quantites of hydrocarbons such as ethane and propane.
See also: fossil fuel

natural hazards

Events that result from natural processes and that have significant impacts on human beings.


The geologic time period extending from 23 to 2.6 million years ago. During the Neogene, global climate cooled, the continents moved close to their current positions, mammals and birds continued to evolve, and the first hominins appeared.
The Neogene is a portion of the Cenozoic.

Newark Supergroup

A sequence of nonmarine sedimentary rocks that accumulated in rift basins along what is now eastern North America (North Carolina to Newfoundland) in the late Triassic to early Jurassic periods. The rifts formed as Pangaea split apart. In some places the strata contain well-preserved fish fossils or dinosaur tracks.


A ductile, silvery-white metallic element (Ni). Nickel in its pure form is rarely found on Earth’s surface; large quantites of nickel are typically found in meteorites. On Earth, nickel is generally found in combination with iron.
Nickel is resistant to corrosion and is commonly used to plate metals, coat chemistry equipment, and manufacture alloys such as electrum.


A small, irregular or rounded mineral deposit that has a different composition from the sedimentary rock that encloses it. Nodules typically form when minerals precipitate from a supersaturated solution within or around features such as biotic remains.


Pertaining to a reaction, as in fission, fusion, or radioactive decay, that alters the energy, composition, or structure of an atomic nucleus.